The human health burden of non-typhoidal Salmonella enterica and Vibrio parahaemolyticus foodborne gastroenteritis in Shanghai, east China.

Information on the burden of disease due to foodborne pathogens in China is quite limited. To understand the incidence of foodborne gastroenteritis due to non-typhoidal Salmonella enterica and Vibrio parahaemolyticus, population survey and sentinel hospital surveillance were conducted during July 2010 to June 2011 in Shanghai, east China, and a model for calculating disease burden was established. The multiplier for gastroenteritis caused by these pathogens was estimated at 59 [95% confidence interval (CI) 30-102]. Annual incidence per 100,000 population in Shanghai was estimated as 48 (95% CI 24-83) and 183 (95% CI 93-317) cases for foodborne non-typhoidal salmonellosis and V. parahaemolyticus gastroenteritis, respectively, illustrating that bacterial gastroenteritis due to these two pathogens poses a substantial health burden. There is a significant difference between our simulated incidence and the data actually reported for foodborne diseases, indicating significant underreporting and underdiagnosis of non-typhoidal S. enterica and V. parahaemolyticus gastroenteritis in the surveillance area. The present research demonstrates basic situation of the health burden caused by major foodborne pathogens in the surveillance area. Enhanced laboratory-based sentinel hospital surveillance is one of the effective ways to monitor food safety in east China.

Introduction

Foodborne disease is an important public health issue worldwide, and it is also China’s number one food safety issue, causing a huge burden of disease and major economic losses [1-7]. Effective control of foodborne diseases needs to be based on information from foodborne disease burden assessments, but the true burden of foodborne diseases in China is not cleared yet. Chinese foodborne disease passive surveillance systems mainly collect information on outbreaks and rarely collect information on sporadic diseases [8]. According to the Management of Food Poisoning Incidents released in 1999: “Units where food poisoning or suspected food poisoning incidents occurred and those that receive food poisoning or suspected food poisoning patients for treatment should report the relevant information to the local health administrative department in a timely manner [9].” Since only a small fraction of foodborne diseases occur relative to identified outbreaks, reported foodborne disease through the passive surveillance system is often insufficient [10]. To overcome the inherent defects of passive surveillance, the United States [2, 3, 11], the United Kingdom [4, 12], the Netherlands [6], Australia [5], Canada [13], Jordan [14], and Japan [15], have conducted research to better estimate the burden of foodborne disease and foodborne pathogens more accurately, however, only one study was conducted in south China [16], and such studies were lacking in east China.

Estimating the burden of disease for specific foodborne pathogens is necessary for precisely estimating foodborne disease burden and monitoring the impact of management measures to prevent and control foodborne disease. Assessing the burden of foodborne disease is complicated because it is difficult to determine whether the disease is absolutely associated with food. Acute gastrointestinal illness (AGI) is a common form of foodborne disease. Research ascertaining the burden of AGI and the proportion of foodborne pathogens among patients provides important basic data for estimating foodborne disease burden [17]. Studies to estimate community pathogen-specific incidence can be of two designs: (1) community-based AGI cohort study [6, 18], and (2) estimate the monitoring data multiplier by using additional data [14–16, 19, 20].

For specific and effective control measures, it is necessary to determine foodborne disease severity. From 2010 to 2011, the Shanghai Municipal Center for Disease Control and Prevention launched a pilot project for active surveillance of foodborne diseases. Non-typhoidal Salmonella enterica and Vibrio parahaemolyticus are the most common bacteria that cause foodborne disease outbreaks in China [8]. Using data from cross-sectional population survey on AGI, along with sentinel hospital surveillance on specific foodborne pathogens, the health burden of foodborne gastroenteritis in Shanghai of east China caused by these two pathogens was estimated.

Materials and methods

Population survey

To estimate the incidence of AGI in the general population, a twelve-month, face-to-face survey from July 2010 through June 2011 of randomly selected respondents were conducted in Shanghai of east China [7]. The sentinel sites were: Luwan District (population 248,779) and Qinpu District (population 1,081,022). Population in the sentinel sites represents about 5.8% of the total Shanghai permanent resident population (23,019,196) in 2010. Each sentinel site was divided into several blocks according to population proportioned distribution. A total of 251 blocks were generated from the two sentinel sites. Households were randomly selected from each block and the number of households surveyed was proportional to the population size. Within each household, the individual who was next to celebrate his/her birthday was chosen to participate in the survey. Written and informed consent was received from all respondents and parents or guardians of the minors prior to the interview. Proxy respondents were applied for people aged less than 12 and aged between 12–18 in which it was up to the parents or guardians to decide.

AGI was defined as diarrhea of three and above loose stools during any 24-h period or significant vomiting with at least one other symptom, such as fever, abdominal cramps or pain, but excluding those persons who reported their symptoms of diarrhea or vomiting to be due to non-infectious causes such as Crohn’s disease, irritable bowel syndrome, colitis, diverticulitis of large intestine, pregnancy, excess alcohol, chemotherapy/radiotherapy, drugs, or food allergy. The proportion of AGI cases seeking medical care, and the proportion of cases submitting a stool specimen for testing was also determined. Through weighting age, gender, and residence, differences in estimates for survey and target populations were adjusted using the 2010 Shanghai census data [21]. Questionnaire data were entered and analyzed using EpiData version 3.1 (EpiData Association, Odense M, Denmark) and SPSS version 16.0 (SPSS Inc., Chicago, IL, USA).

Sentinel hospital surveillance

During the same period of the population survey, hospital surveillance was carried out at eight sentinel hospitals, among which two were secondary hospitals and six primary hospitals. There was a total of two tertiary hospital, four secondary hospitals and 14 primary hospitals in the surveillance area during the period of 2010 and 2011. A primary hospital was defined as a community hospital that provided primary health services; a secondary hospital was defined as a local hospital that provided comprehensive health services; and a tertiary hospital was defined as a regional hospital that provided comprehensive and specialized health services [22]. Rectal swabs or stool specimens from patients with diarrhea were collected from the sentinel hospitals, and all specimens were tested for non-typhoidal S. enterica and V. parahaemolyticus by the laboratories of the local Center for Disease Control and Prevention. We assumed that the stool samples sent to the hospital laboratories were representative of the community samples.

For S. enterica detection, specimens were enriched in selenite broth, followed by surface plating (or plating) on Bismuth sulfite agar and xylose-lysine-desoxycholate (XLD) agar (or Hektoen enteric agar, CHROMagar Salmonella agar) [23]. With reference to V. parahaemolyticus detection, specimens were enriched in alkaline peptone water, followed by surface plating (or streaking) on thiosulfate citrate bile salts sucrose agar or CHROMagar Vibrio agar [24]. The plates were incubated at 37°C for 18–24 hours. We defined a case of diarrhea as a person with three and above loose stools during any 24-h period.

Burden of disease calculation

We multiplied the sentinel hospital surveillance area population, AGI incidence per person-year, the proportion of cases seeking medical care (the inverse of Multiplier One), and the proportion of cases submitting a stool specimen for testing among those seeking medical care (the inverse of Multiplier Two) to estimate the number of stool specimens submitted in the surveillance area. Then, the number of submitted stool specimens was divided by the number of stool specimens tested to estimate the proportion of laboratory pathogen testing. Multiplier Three is the inverse of the proportion of laboratory pathogen testing.

According to proficiency testing program in Guangdong province, the non-typhoidal S. enterica isolation sensitivity rate of the laboratories was 87.5% [16]. Therefore, it was assumed that the laboratory testing sensitivity in Shanghai was 87.5%, ranging from 85% to 100%. Multiplier Four is the inverse of the proportion of laboratory identifying pathogen.

The above mentioned multipliers were multiplied to estimate the multiplier for these surveillance artifacts (Multiplier Total, MT). Fig 1 shows the pyramid of the burden of pathogen-specific gastroenteritis. To account for uncertainty, multipliers were modeled using the Pert distribution (Table 1) [25]. The estimation model was performed using @RISK (version 7.6, Palisade, Newfield, N.Y.), with 25,000 iterations per estimation. The number of positive specimens tested was multiplied with MT to estimate the number of positive samples in the surveillance area. By using the population of the surveillance area reported in the 2010 census, the estimated annual disease per 100,000 population in the surveillance area were assessed.

Fig 1

Pyramid of the burden of pathogen-specific gastroenteritis.

Table 1

Multipliers used to determine health burden of non-typhoidal salmonellosis and Vibrio parahaemolyticus gastroenteritis in Shanghai, east China, 2010–2011.

Multipliera	Surveillance step	Distribution
Multiplier One (M1)	Cases seeking medical care	Pert (2.1, 2.7, 3.8)
Multiplier Two (M2)	Cases submitting a stool specimen for testing	Pert (1.9, 2.9, 5.9)
Multiplier Three (M3)	Laboratory performing test for pathogens	Pert (2.9, 6.0, 8.9)
Multiplier Four (M4)	Laboratory identifying pathogens	Pert (1.0, 1.1, 2.0)
Multiplier Total (MT)	The multiplier for the total surveillance artifacts	M1*M2*M3*M4

a The multiplier for each surveillance step is the inverse of the proportion responding positively.

Since there are no data on the proportion of foodborne pathogen-specific transmission in China, the proportions were based on data published by Hald et al. for WPR B region (including China) and were multiplied by the number of diseases to obtain foodborne non-typhoidal salmonellosis [26], while the proportion based on US research was used to obtain foodborne V. parahaemolyticus gastroenteritis [2]. The estimated pathogen-specific numbers of foodborne disease cases were compared with the routinely reported numbers of foodborne outbreak cases so as to calibrate the surveillance data [8].

Scientific ethics

The study protocol on population survey and sentinel hospital surveillance was approved in 2010 by the Committee on Human Experimentation of the National Institute for Nutrition and Food Safety, Chinese Center for Disease Control and Prevention. The ethics committee waived the requirement for informed consent from patients with diarrhea.

Results

Between July 2010 and June 2011, 7,176 persons were interviewed (response rate = 99.4%). Distribution of demographic characteristics of residents and survey respondents are shown in Table 2. In general, survey respondents were more likely to be female, older, less educated, larger household size and more likely to live in the rural area than residents. Of the 7,176 persons included in the survey, 108 (1.5%) reported having experienced symptoms of gastroenteritis in the four weeks prior to interview. Of these respondents, eight were declared due to non-infectious causes and included in the non-case group, leaving 100 respondents to be maintained in the case group. The prevalence of AGI in the four weeks prior to interview, adjusted for age, gender, and residence, was 1.2% [95% confidence interval (CI) 1.0–1.5]. This represents an average of 0.16 (95% CI 0.15–0.17) occurrences of AGI per person-year in Shanghai. Among AGI cases, 36.9% (95% CI 26.5–47.2) visited a doctor, and among them 34.4% (95% CI 17.0–51.9) submitted a stool specimen.

Table 2

Distribution of demographic characteristics of residents and survey respondents.

Variable	Proportion of Residents (%)	Proportion of Survey Respondents (%)
Gender
Male	51.5	48.2
Female	48.5	51.8
Age (years)
0–4	3.4	0.5
5–14	5.2	1.6
15–24	16.3	4.3
25–44	36.9	16.6
45–64	28.1	44.3
≥ 65	10.1	32.7
Education
Preschool children	4.1	0.8
Illiterate	3.0	11.4
Primary	13.6	23.4
Secondary	36.5	48.1
Tertiary	21.0	10.6
University	21.9	5.7
Household size (number of person)
1–2	51.5	41.5
≥ 3	48.5	58.5
Household type
No residents < 18 years	n.a.	77.7
At least one resident < 18 years	n.a.	22.3
Residence
Urban	89.3	54.3
Rural	10.7	45.7

Between July 2010 and June 2011, a total of 4,568 patients with diarrhea presented to a hospital participating in surveillance, among which, 4,548 swab/stool specimen were collected and tested. Non-typhoidal S. enterica and V. parahaemolyticus were isolated from 19 (0.4%) and 48 (1.1%), respectively. The month-wise isolation of these pathogens varied between 0–1.7% and 0–3.2%, respectively (Fig 2), while more information regarding the two studied bacterial species was not collected. No detailed personal information was collected on patients with diarrhea.

Fig 2

Month-wise isolation rate for non-typhoidal Salmonella enterica and Vibrio parahaemolyticus in Shanghai, east China, 2010–2011.

According to data from the National Bureau of Statistics, the population in the surveillance area in 2010 was 1,329,801. By multiplying the incidence of AGI 0.16 per person-year, the AGI episodes per year in the surveillance area was estimated to be 212,768. Among persons with AGI, 36.9% sought medical care. Extrapolating this figure to the population of surveillance area indicates that 78,511 persons with AGI sought medical care. Among people seeking medical care, 34.4% submitted a stool specimen for testing. Extrapolating this figure to the population of surveillance area indicates that 27,008 individuals with AGI submitted stool specimens (2,031 specimens/100,000 population). Considering that the number of stool specimens tested in the surveillance area was 4,548, the frequency of laboratory performing test for pathogens was estimated to be 16.8% (Table 3). For each person with laboratory confirmed salmonellosis or V. parahaemolyticus gastroenteritis there were 59 (95% CI 30–102) infected persons in the community (MT).

Table 3

Steps for the calculation of the frequency of laboratory performing test for pathogens in the surveillance area in Shanghai, east China, 2010–2011.

	Mean (95% CI)
AGIa incidence per person-year	0.16 (0.15–0.17)
AGI episodes per year (n)	212,768 (199,470–226,066)
Proportion of cases seeking medical care (%)	36.9 (26.5–47.2)
Medical consultations for AGI per year (n)	78,511 (56,384–100,427)
Proportion of cases submitting a stool specimen (%)	34.4 (17.0–51.9)
No. stool specimens submitted	27,008 (13,347–40,747)
No. stool specimens tested	4,548
Proportion of laboratory pathogen testing (%)	16.8 (11.2–34.1)

a AGI—acute gastrointestinal illness.

The estimated cases in the surveillance area during the 12-month study were 1,121 cases (95% CI 570–1,938) of salmonellosis and 2,832 cases (95% CI 1,440–4,896) of V. parahaemolyticus gastroenteritis (Table 4). Considering the population of the surveillance area, the annual incidence estimated by the model developed herein was 84 (95% CI 43–146) cases for salmonellosis and 213 (95% CI 108–368) cases for V. parahaemolyticus gastroenteritis per 100,000 population. Annual incidence per 100,000 population in Shanghai was estimated as 48 (95% CI 24–83) and 183 (95% CI 93–317) cases for foodborne non-typhoidal salmonellosis and V. parahaemolyticus gastroenteritis, respectively.

Table 4

Estimated health burden of non-typhoidal salmonellosis and Vibrio parahaemolyticus gastroenteritis in Shanghai, east China, 2010–2011.

Pathogen	No. positive specimens	Estimated positive specimens in the surveillance area (95% CI)	Estimated disease cases per 100,000 population (95% CI)	Estimated percentage of foodborne transmission	Estimated foodborne disease cases per 100,000 population (95% CI)	Reported foodborne disease outbreak cases per 100,000 population
Non-typhoidal Salmonella enterica	19	1,121 (570–1,938)	84 (43–146)	57%	48 (24–83)	0.08
Vibrio parahaemolyticus	48	2,832 (1,440–4,896)	213 (108–368)	86%	183 (93–317)	1.71

Discussion

This is the first disease burden report for foodborne pathogens in east China. Using data from a population survey and sentinel hospital surveillance, the burden of foodborne gastroenteritis in Shanghai was estimated to be 11,061 (95% CI 5,624–19,122) cases of salmonellosis and 42,159 (95% CI 21,437–72,886) cases of V. parahaemolyticus gastroenteritis. This indicates that AGI caused by these two pathogens poses a substantial burden in the Shanghai population. While knowing the absolute number of community cases may not be necessary to identify an outbreak, this information is very important for decision makers because it is useful both for formulating public health policies and for estimating the cost of disease.

Our estimate of foodborne salmonellosis (48 cases per 100,000 population) was lower than those estimated in Japan (199 per 100,000) [15], the United Kingdom (220 per 100,000) [27], the United States (340 per 100,000) [2], and Australia (422 per 100,000) [5]. Compared with other data related to China, the foodborne salmonellosis incidence estimated in the present study was lower than that reported for Guangdong province (392 per 100,000) [16], as determined from a literature review (627 per 100,000) [28], and that reported in a global burden study (3,600 per 100,000) [29].

V. parahaemolyticus has been the leading cause of foodborne disease outbreaks in China [8]. Our estimate of foodborne V. parahaemolyticus gastroenteritis (183 per 100,000) was much higher than those estimated in the United Kingdom (<1 per 100,000) [27], Australia (4 per 100,000) [5], the United States (12 per 100,000) [2], and Japan (65 per 100,000) [15]. Shanghai is a coastal province, and previous data reported that the number of foodborne outbreaks of V. parahaemolyticus in this province ranks first in China [30]. Shanghai’s health administration needs to take effective measures to strengthen the prevention and control of foodborne gastroenteritis caused by V. parahaemolyticus.

Diseases are divided into outbreak and sporadic forms. When designing and implementing pathogen-specific foodborne disease burden studies, it is necessary to consider the distinction between outbreak and sporadic cases. As shown by data from Japan and the United States, S. enterica and V. parahaemolyticus infections are mainly sporadic, and outbreaks are less common [2, 15]. Because outbreaks and sporadic diseases have similar case characteristics [31], the analysis of the estimated disease burden based on laboratory-confirmed sporadic cases adopted in this study is feasible. In the present study, the estimates of S. enterica and V. parahaemolyticus were remarkably higher than the numbers reported to passive surveillance as foodborne disease outbreak cases, findings similar to those reported in Japan and the United States, highlighting the fact that many foodborne diseases are not captured in the present passive outbreak surveillance system [2, 15].

It should be recognized that the uncertainty of this study falls within the range of other countries’ estimates [2, 12, 14–16]. For each culture-confirmed case, we estimated that there were 59 cases of salmonellosis or V. parahaemolyticus gastroenteritis in the community. These differences in uncertainty of the study may be mainly due to methodological differences, such as laboratory practices and surveillance systems. In 2011, the China National Center for Food Safety Risk Assessment officially initiated the National Laboratory-based Foodborne Disease Surveillance Network, which includes population surveys and active sentinel surveillance, aiming at estimating the burden of foodborne diseases [32]. However, due to the large number of AGI cases in China, the limited number of existing laboratory monitoring specimens will inevitably cause high uncertainty, resulting in inaccurate estimates of foodborne disease burden. Although cohort studies are more complex and costly, they can provide much more accurate community-specific rates of pathogen-specific infections when combined with laboratory tests of case specimens. In order to more accurately determine and prioritize food safety issues in China, and to evaluate and quantify the burden of foodborne diseases outbreaks, it is necessary to establish a cohort study of acute gastroenteritis including case-test specimens in order to obtain a more accurate incidence of major foodborne pathogen infections, so as to evaluate the burden of foodborne disease.

Other sources of error in the present study may also have affected the estimates. First, we use the proportion of cases submitting a stool specimen from population surveys. In China, people submit stool specimens more for leukocyte testing than for specific pathogens. Thus, we may have overestimated the proportion of persons infected with pathogens who provided stool specimens for culture and, therefore, we may have underestimated the multiplier for this step. Second, we also estimated the rate of laboratory testing sensitivity. Further studies are needed to confirm this estimate, if the actual sensitivity is higher, then our calculations overestimate the burden of disease. Finally, the estimation of community prevalence of infection with individual pathogens from the testing of a relative lower proportion of stool samples from cases is likely to be subject to bias and considerable uncertainty. In the present study, the stool samples were obtained from patients who sought medical care for AGI. AGI visits may be the result of a number of factors, such as urban/rural differences, which could bias whether these samples are representative of the community samples.

When a person is exposed to a foodborne pathogen, their peak response falls on a continuum from no infection to infection (asymptomatic) to disease (symptomatic) to severe disease (hospital) to death. Where the peak response falls on this continuum depends on the outcome of the interaction between the pathogen, host, and food (disease triangle). Consequently, if two communities had the same disease rate but one community had more high-risk individuals, the disease rate would be a poor indicator of health burden because the severity of disease would higher in the community with more high-risk individuals. Therefore, it is necessary to collect data on severity of disease in future researches, and the current assessment could be improved by estimating the health burden that takes severity of disease into account.

Conclusions

In conclusion, the estimated large number of salmonellosis and V. parahaemolyticus gastroenteritis cases occurring every year in the surveillance area indicates that these two pathogens pose a substantial health burden in Shanghai, east China. After considering the differences among distinct pathogens, these methods can also be applied in a similar manner to assess the burden of additional foodborne pathogens. Ongoing studies on the economic burden of major foodborne pathogen infections are necessary to more accurately assess the burden of foodborne disease in China. China should further strengthen global cooperation in the field of foodborne disease burden assessment in order to provide improved data support for global burden estimation of foodborne diseases.

(DOC)

Click here for additional data file.

24 Aug 2020

PONE-D-20-22153

The Human Health Burden of nontyphoidal Salmonella and Vibrio parahaemolyticus Foodborne Gastroenteritis in Shanghai, East China

PLOS ONE

Dear Dr. Chen,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

The Academic Editor would like to apologize to the authors for the long duration of the review process; it was due to the unavailability of multiple reviewers with expertise in the field of surveillance and epidemiology who were invited by the editor to handle the manuscript but could not accept the invitation. Review comments have been timely provided by only one invited reviewer and are attached in the present letter. In order to provide the authors with a timely decision, this manuscript proceeded to the next stage of the editorial process, based on the evaluation provided by one external reviewer and the academic editor herself.

Editor’s comments

Although the Academic Editor is not an epidemiologist, raised comments regarding the overall approach of the presented study from a food microbiology perspective, its scientific soundness as well as the quality of the manuscript are summarized below. According to the editor’s opinion, the manuscript should be subject to minor revisions before its publication in PLOS ONE is considered. Beyond the more specific comments that are following, a general a comment is an overall cross-check with regard to English grammar/syntax (maybe a review by an English expert/native speaker should be considered).

- Title: both in the manuscript’s title and throughout the manuscript, please use the species name “Salmonella enterica” (or S. enterica after first mentioning) instead of the genus name (i.e. Salmonella). The genus Salmonella includes two species (i.e. Salmonella enterica and Salmonella bongori) and only S. enterica is regarded as a foodborne pathogen for humans.

- L24-25: please revise to “…cases for non-typhoidal salmonellosis and V. parahaemolyticus infection, respectively, illustrating that bacterial gastroenteritis due to these two pathogens poses a substantial health burden”

- L27: revise to “…and the data actually reported for foodborne diseases…”

- L45: I would suggest using “relative” instead of “proportionate”

- L48: please correct to “the Netherlands”

- L53: please revise to “…for precisely estimating foodborne disease burden and monitoring the impact…”

- L58-59: please revise to “…among patients provides important basic data for estimating foodborne disease burden”

- L64: the phrase “foodborne pathogenic infections” is rather specific for such a general statement; I would suggest using “foodborne illness severity” instead.

- L92: correct to “eight sentinel hospitals”

- L94-95: please correct to “Rectal swabs or stool specimens from patients with diarrhea were collected from the sentinel hospitals…”

- L96: revise to “non-typhoidal S. enterica and V. parahaemolyticus by the laboratories of the Chinese Center for Disease Control and Prevention”; in general, be consistent using the same single (and not multiple) terms throughout the manuscript, e.g. “non-typhoidal” (instead of “non-typhoid”  or “nontyphoidal”), “foodborne” (instead of “food-borne”), etc.

- L98: please correct to “…were representative of the community samples”

- L99-103: revise to “For S. enterica detection, specimens were enriched in selenite broth, followed by surface plating (or plating) on Bismuth sulfite agar and xylose-lysine-desoxycholate (XLD) agar. With reference to V. parahaemolyticus detection, specimens were enriched in alkaline peptone water, followed by surface plating (or streaking) on thiosulfate citrate bile salts sucrose agar or CHROMagar Vibrio agar”. Moreover, were specific ISO protocols applied for these selective enrichment procedures? If so, please refer to the specific protocols (as in-text citations with the corresponding additions in the references’ list).

- L107-113: it would be better for the reader (particularly a non-expert in epidemiology) if definitions of M1, M2 and M3 are provided in brief

- L111: please change to “Then, the number of submitted stool specimens was divided by…”

- L112: by “laboratory performing test for pathogens” you refer to “laboratory pathogen testing”? If so, consider using the second (simpler) term both here and wherever else applicable in the manuscript’s text.

- L114: change to “It was assumed that the laboratory testing sensitivity was 87.5%...”; in general, use third person (and not “we”) when providing descriptions pertinent to the Materials and Methods and/or Results section of the manuscript.

- L117: please revise to “Figure 1 shows the pyramid of the burden of pathogen-specific foodborne gastroenteritis”

- L118-119: please revise to “…were modeled using the Pert distribution. The estimation model was developed using @RISK…”

- L120: please revise to “The number of positive specimens tested was multiplied with M to estimate the number of sportive samples in the surveillance area”

- L123: please correct to “…were assessed”

- L124: revise to “Pyramid of the burden of pathogen-specific gastroenteritis”. Also, is this the appropriate place in the manuscript’s text for a figure caption (and the same applies for Fig. 2 caption in L157-158)?

- L125-126: please revise to “…non-typhoidal salmonellosis and Vibrio parahaemolyticus infection…”; please use the same phrase when referring to the infection (gastroenteritis) caused by these two pathogens throughout the manuscript for simplification and consistency reasons.

- Table 1: in the last line (referring to M4) and the last column (referring to the distribution) please use a decimal digit for all three numbers (namely, 1.0, 1.1 and 2.0).

- L129-135: please revise as following recommended: “Since there are no data on the proportion…on data published by Hald et al. [23]…and were multiplied by the number of illnesses to obtain foodborne non-typhoidal salmonellosis [23], while the proportion based on US research was used to obtain…The estimated pathogen-specific numbers of foodborne illness cases were compared with the routinely reported numbers of foodborne outbreak cases so as to calibrate the surveillance data”. Please keep in mind that “data” is plural (singular form the Latin word “datum”), and proceed with all required grammar corrections when using this term throughout the manuscript.

- L138: change to “…the National Institute for Nutrition and Food Safety…”

- L149-150: please revise to “…36.9% (95% CI 26.5-47.2) visited a doctor, and among them 34.4% (95% CI 17.0-51.9) submitted a stool specimen”

- L155-156: please correct to “…(Fig. 2), while more information regarding the two studied bacterial species was not collected”

- L157-158: please revise the Figure 2 caption to “Month-wise isolation rate for non-typhoidal Salmonella enterica and Vibrio parahaemolyticus in Shanghai, east China, 2010-2011”

- L165: please correct to “Among people seeking medical care, 34.4%...”

- L168: please correct to “Considering that the number of stool specimens tested in the surveillance area was 4,548…”

- L170: change to “…laboratory confirmed salmonellosis or V. parahaemolyticus infection…”; also to what does “respectively” refer to? (a single percentage, namely 71%, is mentioned herein).

- Table 2: I would suggest moving the percentage symbol (%) in the first (from the second) column of the table in parentheses (wherever applicable), e.g., “AGI incidence per person-year (%)”. Moreover, spell out the AGI abbreviation (either in the title or in a footnote). Finally prefer using “laboratory pathogen testing” in the place of the vaguer “laboratory perming test for pathogens”

- L174-178: please revise to “The estimated cases in the surveillance area during the 12-month study 1,349 cases (95% CI…) of salmonellosis and 3,408 cases (95% CI…) of V. parahaemolyticus infection (Table 3). Considering the population of the surveillance area, the annual incidence estimated by the model developed herein was 101 (95% CI…) cases for salmonellosis abd 256 (95% CI…) cases for V. parahaemolyticus infection per 100,000 population”

- Table 3: Revise the title to “Estimated health burden of non-typhoidal salmonellosis and Vibrio parahaemolyticus infection in Shanghai, east Chine, 2010-2011. Also make the following changes:

1.  Non-typhoidal Salmonella enterica (in 1st column)

2. Estimated foodborne illness cases per 100,000 population (95% CI) (in 4th and 6th column)

3. Reported foodborne illness outbreak cases per 100,000 population (in 7th column)

General comment: avoid using the general term “illness” and try to be consistent and specific by using the term “foodborne illness”; also choose whether you prefer to use “illness” or “disease” and be consistent throughout the manuscript.

- L184: correct to “from a population survey”

- L184-185: revise to “…surveillance, the burden of foodborne gastroenteritis in Shanghai was estimated to be 13,310…”

- L187: revise to “This indicates that AGI caused by these two pathogens poses a substantial burden…”

- L197: revise to “…as determined from a literature review…”

- L210: what about the distinction between outbreak and sporadic cases? Is this possible based on the analysis performed in the present study? I think that a pertinent comment would add value to the Discussion section of the manuscript.

- L215: revise to “…the China National Center…”

- L218” revise to “…estimating the burden…”

- L223-226: please consider revising to “In order to more accurately determine and prioritize food safety issue in China, and to evaluate and quantify the burden of foodborne diseases outbreaks, it is necessary…

- L241-245: please revise to “In conclusion, the estimated large number of salmonellosis and V. parahaemolyticus infection cases occurring every year in the surveillance area, indicates that these two pathogens pose a substantial health burden in Shanghai, east China, After considering the differences among distinct pathogens, these methods can also be applied in a similar manner to assess the burden of additional foodborne pathogens”

- L246: change “infection” to “infections”

- L248: revise to “…in order to provide improved data support…”

- References: please cross-check references with regard to accuracy and conformance to the PLOS ONE format/style

- Figure 2: correct the legends’ text to “Non-typhoidal Salmonella enterica” and “Vibrio parahaemolyticus”

Please submit your revised manuscript by Oct 08 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Alexandra Lianou, Ph.D.

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Please include additional information regarding the survey or questionnaire used in the study and ensure that you have provided sufficient details that others could replicate the analyses. For instance, if you developed a questionnaire as part of this study and it is not under a copyright more restrictive than CC-BY, please include a copy, in both the original language and English, as Supporting Information.

3. In your Methods section, please provide additional information about the demographic details of your participants. Please ensure you have provided sufficient details to replicate the analyses such as: a)  a description of any inclusion/exclusion criteria that were applied to participant inclusion in the analysis and b) a table of relevant demographic details.

4. You indicated that you had ethical approval for your study. In your Methods section, please ensure you have also stated whether you obtained consent from parents or guardians of the minors included in the study or whether the research ethics committee or IRB specifically waived the need for their consent.

5. In the ethics statement in the manuscript and in the online submission form, please provide additional information about the patient records used in the retrospective hospital surveillance arm of your study. Specifically, please ensure that you have discussed whether all data were fully anonymized before you accessed them and/or whether the IRB or ethics committee waived the requirement for informed consent. If patients provided informed written consent to have data from their medical records used in research, please include this information.

6. PLOS requires an ORCID iD for the corresponding author in Editorial Manager on papers submitted after December 6th, 2016. Please ensure that you have an ORCID iD and that it is validated in Editorial Manager. To do this, go to ‘Update my Information’ (in the upper left-hand corner of the main menu), and click on the Fetch/Validate link next to the ORCID field. This will take you to the ORCID site and allow you to create a new iD or authenticate a pre-existing iD in Editorial Manager. Please see the following video for instructions on linking an ORCID iD to your Editorial Manager account: https://www.youtube.com/watch?v=_xcclfuvtxQ

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: 1. The Introduction provides justification for conducting a national health burden assessment but does not explain why a local (Shanghai) health burden assessment was conducted. Please explain why a local and not a national health burden assessment was conducted and why Salmonella and Vibrio parahaemolyticus were selected for the assessment.

2. What is the difference between a primary, secondary, and tertiary hospital? Other readers may have similar questions. Therefore, it might be a good idea to include the answer to this question in the manuscript.

3. Is the testing sensitivity the same as the false negative rate? It seems that a range from 50 to 100% is not realistic because no test is perfect and a test with such a low sensitivity of 50% would not be used. It would be a good idea to better explain the basis for these estimates of uncertainty.

4. When I multiply the most likely values for M1, M2, M3, and M4 for the pert distributions in Table 1, I get 51 but the text says the overall multiplier is 71. Why are these values not similar? Other readers may have the same question. Perhaps it would be good to explain in more detail how 71 and its 95% CI were obtained.

5. It is my understanding, based on human feeding trials (McCullough & Eisele, 1951a, 1951b, 1951c, 1951d), that an infection occurs when a patient is shedding the pathogen but not showing symptoms of disease, whereas an illness occurs when a patient is shedding the pathogen and showing symptoms of the disease. In the present study, the incidence of people showing symptoms of gastrointestinal disease was a basis for the calculation of health burden. Thus, the health burden assessment was for illness and not infection. Yet, throughout the paper both terms are used interchangeably, which is a bit confusing. To do a health burden assessment for infection, data would be needed for the incidence of people that test positive for the pathogen but do not show symptoms of illness. That kind of data was not collected in the present study. Thus, I think that it is not appropriate to talk about a health burden assessment for infection when it is actually a health burden assessment for illness.

6. The sentence starting on line 153 seems to be missing its beginning. Thus, its meaning is not clear. Please clarify this sentence.

7. When a person is exposed to a foodborne pathogen, their peak response falls on a continuum from no infection to infection (asymptomatic) to illness (symptomatic) to severe illness (hospital) to death. Where the peak response falls on this continuum depends on the outcome of the interaction between the pathogen, host, and food (disease triangle). Consequently, if two communities had the same illness rate but one community had more high-risk individuals, the illness rate would be a poor indicator of health burden because the severity of illness would higher in the community with more high-risk individuals. Therefore, I think the current manuscript could be improved by estimating a health burden that takes severity of illness into account.

8. Overall, I think this is a very good paper that will be a good addition to the scientific literature. My comments are mainly suggestions that if adopted could improve the manuscript. My main suggestions are to justify conducting a local health burden assessment, to focus the health burden assessment on illness and not infection, and to consider severity of illness in the prediction of health burden.

I hope this review is helpful,

References

McCullough, N. B., & Eisele, C. W. (1951a). Experimental human salmonellosis. I. Pathogenicity of strains of Salmonella meleagridis and Salmonella anatum obtained from spray-dried whole egg. Journal of Infectious Disease, 88, 278-289.

McCullough, N. B., & Eisele, C. W. (1951b). Experimental human salmonellosis. III. Pathogenicity of strains of Salmonella newport, Salmonella derby, and Salmonella bareilly obtained from spray-dried whole egg. Journal of Infectious Disease, 89, 209-213.

McCullough, N. B., & Eisele, C. W. (1951c). Experimental human salmonellosis. IV. Pathogenicity of strains of Salmonella pullorum obtained from spray-dried whole egg. Journal of Infectious Disease, 89, 259-265.

McCullough, N. B., & Eisele, C. W. (1951d). Experimental human salmonellosis: II. Immunity studies following experimental illness with Salmonella meleagridis and Salmonella anatum. Journal of Immunology, 66, 595-608.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

2 Oct 2020

PONE-D-20-22153

The Human Health Burden of non-typhoidal Salmonella enterica and Vibrio parahaemolyticus Foodborne Gastroenteritis in Shanghai, East China

PLOS ONE

Editor’s comments

Although the Academic Editor is not an epidemiologist, raised comments regarding the overall approach of the presented study from a food microbiology perspective, its scientific soundness as well as the quality of the manuscript are summarized below. According to the editor’s opinion, the manuscript should be subject to minor revisions before its publication in PLOS ONE is considered. Beyond the more specific comments that are following, a general a comment is an overall cross-check with regard to English grammar/syntax (maybe a review by an English expert/native speaker should be considered).

Response: I have revised the manuscript via a native English-speaking expert.

- Title: both in the manuscript’s title and throughout the manuscript, please use the species name “Salmonella enterica” (or S. enterica after first mentioning) instead of the genus name (i.e. Salmonella). The genus Salmonella includes two species (i.e. Salmonella enterica and Salmonella bongori) and only S. enterica is regarded as a foodborne pathogen for humans.

Response: Accepted and revised.

- L24-25: please revise to “…cases for non-typhoidal salmonellosis and V. parahaemolyticus infection, respectively, illustrating that bacterial gastroenteritis due to these two pathogens poses a substantial health burden”

Response: Accepted and revised as following:

Annual incidence per 100,000 population in Shanghai was estimated as 48 (95% CI 24–83) and 183 (95% CI 93–317) cases for foodborne non-typhoidal salmonellosis and V. parahaemolyticus gastroenteritis, respectively, illustrating that bacterial gastroenteritis due to these two pathogens poses a substantial health burden. (L23-27)

- L27: revise to “…and the data actually reported for foodborne diseases…”

Response: Accepted and revised.

- L45: I would suggest using “relative” instead of “proportionate”

Response: Accepted and revised. (L47)

- L48: please correct to “the Netherlands”

Response: Accepted and revised. (L50)

- L53: please revise to “…for precisely estimating foodborne disease burden and monitoring the impact…”

Response: Accepted and revised. (L56)

- L58-59: please revise to “…among patients provides important basic data for estimating foodborne disease burden”

Response: Accepted and revised. (L62)

- L64: the phrase “foodborne pathogenic infections” is rather specific for such a general statement; I would suggest using “foodborne illness severity” instead.

Response: Accepted and revised. (L67)

- L92: correct to “eight sentinel hospitals”

Response: Accepted and revised. (L103)

- L94-95: please correct to “Rectal swabs or stool specimens from patients with diarrhea were collected from the sentinel hospitals…”

Response: Accepted and revised. (L109)

- L96: revise to “non-typhoidal S. enterica and V. parahaemolyticus by the laboratories of the Chinese Center for Disease Control and Prevention”; in general, be consistent using the same single (and not multiple) terms throughout the manuscript, e.g. “non-typhoidal” (instead of “non-typhoid” or “nontyphoidal”), “foodborne” (instead of “food-borne”), etc.

Response: Accepted and revised. (L101-111)

- L98: please correct to “…were representative of the community samples”

Response: Accepted and revised. (L113)

- L99-103: revise to “For S. enterica detection, specimens were enriched in selenite broth, followed by surface plating (or plating) on Bismuth sulfite agar and xylose-lysine-desoxycholate (XLD) agar. With reference to V. parahaemolyticus detection, specimens were enriched in alkaline peptone water, followed by surface plating (or streaking) on thiosulfate citrate bile salts sucrose agar or CHROMagar Vibrio agar”. Moreover, were specific ISO protocols applied for these selective enrichment procedures? If so, please refer to the specific protocols (as in-text citations with the corresponding additions in the references’ list).

Response: Accepted and revised as following:

For S. enterica detection, specimens were enriched in selenite broth, followed by surface plating (or plating) on Bismuth sulfite agar and xylose-lysine-desoxycholate (XLD) agar (or Hektoen enteric agar, CHROMagar Salmonella agar) [23]. With reference to V. parahaemolyticus detection, specimens were enriched in alkaline peptone water, followed by surface plating (or streaking) on thiosulfate citrate bile salts sucrose agar or CHROMagar Vibrio agar [24].

- L107-113: it would be better for the reader (particularly a non-expert in epidemiology) if definitions of M1, M2 and M3 are provided in brief

Response: Accepted and revised. (L125-139)

- L111: please change to “Then, the number of submitted stool specimens was divided by…”

Response: Accepted and revised. (L128)

- L112: by “laboratory performing test for pathogens” you refer to “laboratory pathogen testing”? If so, consider using the second (simpler) term both here and wherever else applicable in the manuscript’s text.

Response: Accepted and revised. (L125, 126, 197)

- L114: change to “It was assumed that the laboratory testing sensitivity was 87.5%...”; in general, use third person (and not “we”) when providing descriptions pertinent to the Materials and Methods and/or Results section of the manuscript.

Response: Accepted and revised. (L127-128)

- L117: please revise to “Figure 1 shows the pyramid of the burden of pathogen-specific foodborne gastroenteritis”

Response: Accepted and revised. (L141-142)

- L118-119: please revise to “…were modeled using the Pert distribution. The estimation model was developed using @RISK…”

Response: Accepted and revised. (L143-144)

- L120: please revise to “The number of positive specimens tested was multiplied with M to estimate the number of sportive samples in the surveillance area”

Response: Accepted and revised. (L145-146)

- L123: please correct to “…were assessed”

Response: Accepted and revised. (L149)

- L124: revise to “Pyramid of the burden of pathogen-specific gastroenteritis”. Also, is this the appropriate place in the manuscript’s text for a figure caption (and the same applies for Fig. 2 caption in L157-158)?

Response: Accepted and revised. (L150)

- L125-126: please revise to “…non-typhoidal salmonellosis and Vibrio parahaemolyticus infection…”; please use the same phrase when referring to the infection (gastroenteritis) caused by these two pathogens throughout the manuscript for simplification and consistency reasons.

Response: Accepted and revised. (L151-152)

- Table 1: in the last line (referring to M4) and the last column (referring to the distribution) please use a decimal digit for all three numbers (namely, 1.0, 1.1 and 2.0).

Response: Accepted and revised.

- L129-135: please revise as following recommended: “Since there are no data on the proportion…on data published by Hald et al. [23]…and were multiplied by the number of illnesses to obtain foodborne non-typhoidal salmonellosis [23], while the proportion based on US research was used to obtain…The estimated pathogen-specific numbers of foodborne illness cases were compared with the routinely reported numbers of foodborne outbreak cases so as to calibrate the surveillance data”. Please keep in mind that “data” is plural (singular form the Latin word “datum”), and proceed with all required grammar corrections when using this term throughout the manuscript.

Response: Accepted and revised as following.

Since there are no data on the proportion of foodborne pathogen-specific transmission in China, the proportions were based on data published by Hald et al. for WPR B region (including China) and were multiplied by the number of diseases to obtain foodborne non-typhoidal salmonellosis [26], while the proportion based on US research was used to obtain foodborne V. parahaemolyticus gastroenteritis [2]. The estimated pathogen-specific numbers of foodborne disease cases were compared with the routinely reported numbers of foodborne outbreak cases so as to calibrate the surveillance data [8]. (L156-163)

- L138: change to “…the National Institute for Nutrition and Food Safety…”

Response: Accepted and revised. (L164)

- L149-150: please revise to “…36.9% (95% CI 26.5-47.2) visited a doctor, and among them 34.4% (95% CI 17.0-51.9) submitted a stool specimen”

Response: Accepted and revised. (L179-180)

- L155-156: please correct to “…(Fig. 2), while more information regarding the two studied bacterial species was not collected”

Response: Accepted and revised. (L191-192)

- L157-158: please revise the Figure 2 caption to “Month-wise isolation rate for non-typhoidal Salmonella enterica and Vibrio parahaemolyticus in Shanghai, east China, 2010-2011”

Response: Accepted and revised. (L194-195)

- L165: please correct to “Among people seeking medical care, 34.4%...”

Response: Accepted and revised. (L202)

- L168: please correct to “Considering that the number of stool specimens tested in the surveillance area was 4,548…”

Response: Accepted and revised. (L205)

- L170: change to “…laboratory confirmed salmonellosis or V. parahaemolyticus infection…”; also to what does “respectively” refer to? (a single percentage, namely 71%, is mentioned herein).

Response: Accepted and revised. (L208)

- Table 2: I would suggest moving the percentage symbol (%) in the first (from the second) column of the table in parentheses (wherever applicable), e.g., “AGI incidence per person-year (%)”. Moreover, spell out the AGI abbreviation (either in the title or in a footnote). Finally prefer using “laboratory pathogen testing” in the place of the vaguer “laboratory perming test for pathogens”

Response: Accepted and revised. (L211)

- L174-178: please revise to “The estimated cases in the surveillance area during the 12-month study 1,349 cases (95% CI…) of salmonellosis and 3,408 cases (95% CI…) of V. parahaemolyticus infection (Table 3). Considering the population of the surveillance area, the annual incidence estimated by the model developed herein was 101 (95% CI…) cases for salmonellosis abd 256 (95% CI…) cases for V. parahaemolyticus infection per 100,000 population”

Response: Accepted and revised. (L199-205)

The estimated cases in the surveillance area during the 12-month study were 1,121 cases (95% CI570–1,938) of salmonellosis and 2,832 cases (95% CI 1,440–4,896) of V. parahaemolyticus gastroenteritis (Table 4). Considering the population of the surveillance area, the annual incidence estimated by the model developed herein was 84 (95% CI 43–146) cases for salmonellosis and 213 (95% CI 108–368) cases for V. parahaemolyticus gastroenteritis per 100,000 population. Annual incidence of foodborne gastroenteritis per 100,000 population in Shanghai was estimated as 48 (95% CI (24–83) for non-typhoidal salmonellosis and 183 (95% CI93–317) cases for V. parahaemolyticus gastroenteritis.

- Table 3: Revise the title to “Estimated health burden of non-typhoidal salmonellosis and Vibrio parahaemolyticus infection in Shanghai, east Chine, 2010-2011. Also make the following changes:

1. Non-typhoidal Salmonella enterica (in 1st column)

2. Estimated foodborne illness cases per 100,000 population (95% CI) (in 4th and 6th column)

3. Reported foodborne illness outbreak cases per 100,000 population (in 7th column)

Response: Accepted and revised. (L207-208)

General comment: avoid using the general term “illness” and try to be consistent and specific by using the term “foodborne illness”; also choose whether you prefer to use “illness” or “disease” and be consistent throughout the manuscript.

Response: Accepted and revised.

- L184: correct to “from a population survey”

Response: Accepted and revised. (L228)

- L184-185: revise to “…surveillance, the burden of foodborne gastroenteritis in Shanghai was estimated to be 13,310…”

Response: Accepted and revised. (L228-229)

- L187: revise to “This indicates that AGI caused by these two pathogens poses a substantial burden…”

Response: Accepted and revised. (L232)

- L197: revise to “…as determined from a literature review…”

Response: Accepted and revised. (L242)

- L210: what about the distinction between outbreak and sporadic cases? Is this possible based on the analysis performed in the present study? I think that a pertinent comment would add value to the Discussion section of the manuscript.

Response: Accepted and added sentences as following. (L252-258)

Diseases are divided into outbreak and sporadic forms. When designing and implementing pathogen-specific foodborne disease burden studies, it is necessary to consider the distinction between outbreak and sporadic cases. As shown by data from Japan and the United States, Salmonella and V. parahaemolyticus infections are mainly sporadic, and outbreaks are less common [2, 15]. Because outbreaks and sporadic diseases have similar case characteristics [31], the analysis of the estimated disease burden based on laboratory-confirmed sporadic cases adopted in this study is feasible.

- L215: revise to “…the China National Center…”

Response: Accepted and revised. (L269)

- L218” revise to “…estimating the burden…”

Response: Accepted and revised. (L271)

- L223-226: please consider revising to “In order to more accurately determine and prioritize food safety issue in China, and to evaluate and quantify the burden of foodborne diseases outbreaks, it is necessary…

Response: Accepted and revised. (L277-278)

- L241-245: please revise to “In conclusion, the estimated large number of salmonellosis and V. parahaemolyticus infection cases occurring every year in the surveillance area indicates that these two pathogens pose a substantial health burden in Shanghai, east China, After considering the differences among distinct pathogens, these methods can also be applied in a similar manner to assess the burden of additional foodborne pathogens”

Response: Accepted and revised. (L328-333)

In conclusion, the estimated large number of salmonellosis and V. parahaemolyticus gastroenteritis cases occurring every year in the surveillance area, indicates that these two pathogens pose a substantial health burden in Shanghai, east China. After considering the differences among distinct pathogens, these methods can also be applied in a similar manner to assess the burden of additional foodborne pathogens.

- L246: change “infection” to “infections”

Response: Accepted and revised. (L334)

- L248: revise to “…in order to provide improved data support…”

Response: Accepted and revised. (L336)

- References: please cross-check references with regard to accuracy and conformance to the PLOS ONE format/style

Response: Accepted and revised. (L262, L271)

- Figure 2: correct the legends’ text to “Non-typhoidal Salmonella enterica” and “Vibrio parahaemolyticus”

Response: Accepted and revised. (L194)

When submitting your revision, we need you to address these additional requirements.

2. Please include additional information regarding the survey or questionnaire used in the study and ensure that you have provided sufficient details that others could replicate the analyses. For instance, if you developed a questionnaire as part of this study and it is not under a copyright more restrictive than CC-BY, please include a copy, in both the original language and English, as Supporting Information.

Response: Accepted and include a questionnaire as Supporting Information.

3. In your Methods section, please provide additional information about the demographic details of your participants. Please ensure you have provided sufficient details to replicate the analyses such as: a) a description of any inclusion/exclusion criteria that were applied to participant inclusion in the analysis and b) a table of relevant demographic details.

Response: Accepted and added a sentence as following:

but excluding those persons who reported their symptoms of diarrhea or vomiting to be due to non-infectious causes such as Crohn’s disease, irritable bowel syndrome, colitis, diverticulitis of large intestine, pregnancy, excess alcohol, chemotherapy/radiotherapy, drugs, or food allergy. (L92-95)

Also, a table of relevant demographic details was added, see L183.

4. You indicated that you had ethical approval for your study. In your Methods section, please ensure you have also stated whether you obtained consent from parents or guardians of the minors included in the study or whether the research ethics committee or IRB specifically waived the need for their consent.

Response: Accepted and added sentences as following:

Written and informed consent was received from all respondents and parents or guardians of the minors prior to the interview. (L86-87)

The ethics committee waived the requirement for informed consent from patients with diarrhea. (L167-168)

5. In the ethics statement in the manuscript and in the online submission form, please provide additional information about the patient records used in the retrospective hospital surveillance arm of your study. Specifically, please ensure that you have discussed whether all data were fully anonymized before you accessed them and/or whether the IRB or ethics committee waived the requirement for informed consent. If patients provided informed written consent to have data from their medical records used in research, please include this information.

Response: Accepted and added sentences as following:

No detailed personal information was collected on patients with diarrhea. (L192-193)

Reviewer #1:

1. The Introduction provides justification for conducting a national health burden assessment but does not explain why a local (Shanghai) health burden assessment was conducted. Please explain why a local and not a national health burden assessment was conducted and why Salmonella and Vibrio parahaemolyticus were selected for the assessment.

Response: Accepted and added sentences as following:

From 2010 to 2011, the Shanghai Municipal Center for Disease Control and Prevention launched a pilot project for active surveillance of foodborne diseases. Non-typhoidal Salmonella enterica and Vibrio parahaemolyticus are the most common bacteria that cause foodborne disease outbreaks in China [8]. (L67-70)

2. What is the difference between a primary, secondary, and tertiary hospital? Other readers may have similar questions. Therefore, it might be a good idea to include the answer to this question in the manuscript.

Response: Accepted and added sentences as following:

A primary hospital was defined as a community hospital that provided primary health services; a secondary hospital was defined as a local hospital that provided comprehensive health services; and a tertiary hospital was defined as a regional hospital that provided comprehensive and specialized health services [22]. (L105-109)

3. Is the testing sensitivity the same as the false negative rate? It seems that a range from 50 to 100% is not realistic because no test is perfect and a test with such a low sensitivity of 50% would not be used. It would be a good idea to better explain the basis for these estimates of uncertainty.

Response: Accepted and revised as following:

According to Proficiency testing program in Guangdong province, the Salmonella isolation sensitivity rate of the laboratories was 87.5% (L134-135)

4. When I multiply the most likely values for M1, M2, M3, and M4 for the pert distributions in Table 1, I get 51 but the text says the overall multiplier is 71. Why are these values not similar? Other readers may have the same question. Perhaps it would be good to explain in more detail how 71 and its 95% CI were obtained.

Response: Accepted and revised as following:

The above mentioned multipliers were multiplied to estimate the multiplier for these surveillance artifacts (Multiplier Total, MT). (L140-141)

For each person with laboratory confirmed salmonellosis or V. parahaemolyticus gastroenteritis there were 59 (95% CI30–102) infected persons in the community (MT). (L194-195)

5. It is my understanding, based on human feeding trials (McCullough & Eisele, 1951a, 1951b, 1951c, 1951d), that an infection occurs when a patient is shedding the pathogen but not showing symptoms of disease, whereas an illness occurs when a patient is shedding the pathogen and showing symptoms of the disease. In the present study, the incidence of people showing symptoms of gastrointestinal disease was a basis for the calculation of health burden. Thus, the health burden assessment was for illness and not infection. Yet, throughout the paper both terms are used interchangeably, which is a bit confusing. To do a health burden assessment for infection, data would be needed for the incidence of people that test positive for the pathogen but do not show symptoms of illness. That kind of data was not collected in the present study. Thus, I think that it is not appropriate to talk about a health burden assessment for infection when it is actually a health burden assessment for illness.

Response: Accepted and the health burden assessment was for disease.

6. The sentence starting on line 153 seems to be missing its beginning. Thus, its meaning is not clear. Please clarify this sentence.

Response: Accepted and revised as following:

Between July 2010 and June 2011, a total of 4,568 patients with diarrhea presented to a hospital participating in surveillance, among which, 4,548 swab/stool specimen were collected and tested. (L174-176)

7. When a person is exposed to a foodborne pathogen, their peak response falls on a continuum from no infection to infection (asymptomatic) to illness (symptomatic) to severe illness (hospital) to death. Where the peak response falls on this continuum depends on the outcome of the interaction between the pathogen, host, and food (disease triangle). Consequently, if two communities had the same illness rate but one community had more high-risk individuals, the illness rate would be a poor indicator of health burden because the severity of illness would higher in the community with more high-risk individuals. Therefore, I think the current manuscript could be improved by estimating a health burden that takes severity of illness into account.

Response: Accepted and revised as following:

When a person is exposed to a foodborne pathogen, their peak response falls on a continuum from no infection to infection (asymptomatic) to disease (symptomatic) to severe disease (hospital) to death. Where the peak response falls on this continuum depends on the outcome of the interaction between the pathogen, host, and food (disease triangle). Consequently, if two communities had the same disease rate but one community had more high-risk individuals, the disease rate would be a poor indicator of health burden because the severity of disease would higher in the community with more high-risk individuals. Therefore, it is necessary to collect data on severity of disease in future researches, and the current assessment could be improved by estimating the health burden that takes severity of disease into account. (L317-326)

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

28 Oct 2020

The Human Health Burden of non-typhoidal Salmonella enterica and Vibrio parahaemolyticus Foodborne Gastroenteritis in Shanghai, East China

PONE-D-20-22153R1

Dear Dr. Chen,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Alexandra Lianou, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

All comments raised have been sufficiently addressed in the revised manuscript.

Reviewers' comments:

4 Nov 2020

PONE-D-20-22153R1

The Human Health Burden of non-typhoidal Salmonella enterica and Vibrio parahaemolyticus Foodborne Gastroenteritis in Shanghai, East China

Dear Dr. Chen:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Alexandra Lianou

Academic Editor

PLOS ONE