Feasibility of an online antigen self-testing strategy for SARS-CoV-2 addressed to health care and education professionals in Catalonia (Spain). The TESTA'T- COVID Project.

We aimed to assess the feasibility of TESTA'T COVID strategy among healthcare and education professionals.in Spain during the peak of the 6th wave caused by Omicron variant. Kits were ordered online and sent by mail, participants answered an online acceptability/usability survey and uploaded the picture of results. 492 participants ordered a test, 304 uploaded the picture (61.8%). Eighteen positive cases were detected (5.9%). 92.2% were satisfied/very satisfied with the intervention; and 92.5% found performing the test easy/very easy. We demonstrated that implementing online COVID-19 self-testing in schools and healthcare settings in Spain is feasible.

Introduction

It has been estimated that nearly half of the transmissions of SARS-CoV-2 occur from asymptomatic individuals [1]. As for other infections, the screening of asymptomatic individuals at risk of being exposed to SARS-CoV-2 in order to detect and isolate infected persons early is one of the basic non-pharmaceutical preventive interventions shown to decrease incidence at the community level [2]. Antigen-detecting rapid diagnostic tests (Ag-RDTs) have been proposed as suitable tools for point-of-care screening of individuals potentially exposed and have promising performance characteristics for mass population testing [3]. The main advantages of Ag-RDTs include low price, the lack of need for high-tech laboratory referral, and a short turnaround time to provide a result [2,4]. There are concerns about the high rate of false negatives in Ag-RDTs, a Cochrane review reported variations in sensitivities between brands ranging from 34% to 88% [5]. Even though Ag-RDTs have less sensitivity that real-time polymerase chain reaction (rt-PCR), they reliably identify people with high viral loads, showing high sensitivity that increases with lower cycle threshold (Ct) values (Ct <25, 98.2%; Ct<30, 94.9%) [4]. A previous study demonstrated that Ag-RDTs showed a better correlation with cell culture than rt-PCR [6], so, while rt-PCR is the gold standard for COVID-19 detection, Ag-RDTs are more efficient to detect infectious patients. rt-PCR is a highly sensitive technique that can detect viral RNA for prolonged periods and detects non-transmittable SARS-CoV-2 RNA. This could overestimate the number of contagious patients [7].

Although some contradictory findings have been reported, Ag-RDTs used as self-tests by the general population have a similar accuracy to when they are performed by health professionals [4-7].

Healthcare professionals, who are in contact with many patients, are at a high risk of exposure and, eventually if infected, of transmitting it to vulnerable patients. Above all, the most vulnerable ones such as oncological and immunosuppressed patients. The WHO recommends early detection of SARS-CoV-2 infection among health workers through syndromic surveillance and/or regular testing [8]. Little is known about the level of exposure of teachers and other professionals in the field of education, nevertheless the high transmissibility of the Omicron variant has also dramatically increased prevalence and incidence of SARS-CoV-2 in schools, where exposure is high as well.

Self-testing based on Ag-RDTs could increase access to testing and early confirmation of cases, and thus, reducing transmission. We were interested in investigating the acceptability and feasibility of self-testing in two key populations. We implemented a pilot intervention based on online offering of self-test kits for the SARS-CoV-2 rapid antigen test (TESTA’T COVID) during the peak of the 6th wave caused by the Omicron variant of SARS-CoV-2 in Catalonia (Spain). The objective of the study was to assess the feasibility of TESTA’T COVID strategy among healthcare and education professionals.

Methods

Study design

Non-randomized prospective study.

Study sitting and timing

Data were collected prospectively during the peak of the 6th wave due to the Omicron variant of SARS-CoV-2 in Catalonia, from 15 December 2021 to 15 February 2022.

Study population

The study targeted two different key populations: 1) Staff of the Catalan Institute of Oncology (ICO), a public non-profit organization attached to the Catalan Health Service focused on cancer care and with 1,400 professionals distributed in 5 tertiary hospitals in Catalonia (Spain). 2) Staff of the schools belonging to the COVID Sentinel School Network of Catalonia (CSSNC), which monitors SARS-CoV-2 infection and its determinants, by means of repetitive cross-sectional surveys and includes 23 participating sentinel schools and 700 employees [9].

Inclusion criteria were being 18 years old or older, being staff of ICO or CSSNC, and signing the online informed consent.

Sampling and sample size

Health care workers of the ICO and teachers and school staff from all participating schools of the CSSNC were invited to participate by email. The expected number of participants to recruit was 500. Respondents accessed the study website (https://www.testate.org/), signed up and accepted through an online written and self-complimented informed consent form. Then, participants requested a free COVID-19 rapid lateral flow home test kit (PanBIO ™ COVID-19 Antigen Self-Test, Abbot Laboratories, Chicago, US) and provided contact details including a postal address. Kits included a pictorial leaflet with guidance on how to perform the test and an instructional video was available on YouTube.

Tools of data collection

After performing the test, participants completed an online and self-complimented survey on the project website including sociodemographic characteristics (gender, age, job position), clinical data (presenting symptoms compatible with COVID-19, days since symptoms” onset, vaccination status, number of vaccine’s doses and kind of vaccine), satisfaction with the intervention (Likert-type scale), willingness to repeat the self-test in the future, ease of use of the kit, level of trust in having done a correct interpretation of the obtained result, confidence in the results obtained with Ag self-tests, interest in having available the self-test in their workplace, preferred place to repeat the test (health care centre, do it themselves at home, other), perceived advantages and disadvantages of self-tests, result obtained, and a picture of the result. These pictures were assessed blind by the field coordinator and a microbiologist to check if the reading had been done correctly. The field coordinator and the microbiologist read the results of the pictures uploaded on the project website by the participants without knowing the interpretation made by the participants and by the other member of the research team. All participants with a positive result were contacted and were recommended both to self-isolate and to contact their General Practitioner (GP) as soon as possible.

Study outcomes data management

The main outcome of the study was to evaluate the feasibility of the TESTATE COVID testing strategy among its users. The assessment was based on a conceptual framework adapted from earlier models [10,11]. The adapted framework divides the concept of feasibility into learnability, willingness, suitability, satisfaction, and efficacy (Fig 1). Learnability was defined as the ability of the participant to understand how to correctly perform the self-test and accurately read the test results. Willingness was defined as the intention of participants to follow all the procedure. Suitability was defined as participants’ belief that the test is relevant for their work and that test results are a true indication of the presence or absence of SARS-CoV-2 infection. Satisfaction was described as feeling that being tested for COVID-19 through the TESTATE intervention was convenient and that it is a process they would experience again. Efficacy was defined as participants’ ability to make the effort and time to order the self-testing kit, perform the test, report the obtained result, as well as follow the linkage to care procedure if necessary.

Fig 1

Conceptual framework for the evaluation of a pilot intervention based on offering online COVID-19 self-test kits addressed to healthcare and education professionals in Spain, adapted from Asiimwe et al. 2012 and Ansbro et al. 2015.

The secondary outcomes of the study were the prevalence of SARS-CoV-2 infection among health care and education professionals and the linkage to care rate for those with a positive result. We estimated the SARS-CoV-2 infection prevalence by calculating the proportion of individuals with a positive result over the total number of individuals who uploaded a picture of the obtained. Confidence interval 95% was calculated. The linkage to care rate was assessed by calculating the proportion of individuals who self-reported having contacted their general practitioner and isolated themselves.

A descriptive analysis was carried out, comparing socio-demographic and clinical characteristics and acceptance and usability dimensions among health care and education professionals. Qualitative variables were compared using Pearson’s χ2 test. Quantitative variable comparisons were made between 2 or more groups using non-parametric tests (Kruskal-Wallis). For all analyses, a significance level of 5% was considered. All analyses were done using R version 4.0.5.

Ethical considerations

Confidentiality was guaranteed in accordance with the provisions of the Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016 and the new national Organic Law of Protection of Personal Data (3/2018, 5 December, Data Protection and Digital Rights Act). All participants were provided with online information about the study and given the opportunity to ask questions and clarify queries with the study coordinator by email or phone. The study was approved by the Ethical Committee of the Germans Trias i Pujol Hospital (PI-20-368).

Results

During the study period 297 educators and 195 health professionals ordered a self-sampling kit, and 192 teachers (64.6%) and 111 health professionals (56.9%) correctly uploaded a picture of their result and answered the online survey (p: 0.1035) (Fig 2). Sociodemographic and clinical characteristics of participants are shown in Table 1. The median age of participants was 43.0 (IQR: 20.0–78.0), 80.1% were women. Most participants had received the COVID-19 vaccine (98.7%), among those vaccinated, 63.2% had had three doses and 30.0% had had two. No significative differences between health care and education professionals were observed except for the number of received doses of the COVID-19 that was higher for health care professionals because they were one of the first groups who received the third dose. Differences were also observed in the kind of vaccines received, 27% of education professionals were vaccinated with Astra Zeneca (Cambridge, United Kingdom) while none of the health professionals received this vaccine (Table 1).

Fig 2

Summary of self-tests ordered and results obtained.

December 2021 –January 2022. Catalonia (Spain).

Table 1

Characteristics of the participants in the pilot intervention TESTA’T COVID, Spain December 2021 -January 2022.

N: 307.

		Education professionals	Health care professionals
	All n(%)	n(%)	n(%)
	N = 307	N = 196	N = 111	p value
Gender				0.694
Women	246 (80.1%)	155 (79.1%)	91 (82.0%)
Men	59 (19.2%)	39 (19.9%)	20 (18.0%)
DK	2 (0.65%)	2 (1.02%)	0 (0.00%)
Age
Median (Interquatilic Range)	42.4 (10.3)	42.1 (10.3)	42.8 (10.4)	0.587
Country of birth				0.010
Spain	294 (95.8%)	192 (98.0%)	102 (91.9%)
Other	12 (3.91%)	3 (1.53%)	9 (8.11%)
Dk/Da	1 (0.33%)	1 (0.51%)	0 (0.00%)
Job health care professionals				<0.001
Doctor	17 (5.54%)	0 (0.00%)	17 (15.3%)
Nurse	29 (9.45%)	0 (0.00%)	29 (26.1%)
Nurse assistant	4 (1.30%)	0 (0.00%)	4 (3.60%)
Psychologist	3 (0.98%)	0 (0.00%)	3 (2.70%)
Pharmacist	4 (1.30%)	0 (0.00%)	4 (3.60%)
Administrative staff	8 (2.61%)	0 (0.00%)	8 (7.21%)
Manager	6 (1.95%)	0 (0.00%)	6 (5.41%)
Other	39 (12.7%)	0 (0.00%)	39 (35.1%)
Dk/Da	1 (0.33%)	0 (0.00%)	1 (0.90%)
N/A	196 (63.8%)	196 (100%)	0 (0.00%)
Job education professionals				<0.001
Teacher	156 (50.8%)	156 (79.6%)	0 (0.00%)
Psychologist	1 (0.33%)	1 (0.51%)	0 (0.00%)
Manager	19 (6.19%)	19 (9.69%)	0 (0.00%)
Administrative staff	6 (1.95%)	6 (3.06%)	0 (0.00%)
Responsable/monitor de menjador	1 (0.33%)	1 (0.51%)	0 (0.00%)
Conserge	3 (0.98%)	3 (1.53%)	0 (0.00%)
Altre	9 (2.93%)	9 (4.59%)	0 (0.00%)
Dk/Da	1 (0.33%)	1 (0.51%)	0 (0.00%)
N/A	111 (36.2%)	0 (0.00%)	111 (100%)
Presents covid symptoms				0.849
Yes	63 (20.5%)	42 (21.4%)	21 (18.9%)
No	241 (78.5%)	152 (77.6%)	89 (80.2%)
Dk/Da	3 (0.98%)	2 (1.02%)	1 (0.90%)
Days since sympthoms’ onset				0.298
Same day	4 (1.30%)	3 (1.53%)	1 (0.90%)
1 day	6 (1.95%)	3 (1.53%)	3 (2.70%)
2 days	14 (4.56%)	11 (5.61%)	3 (2.70%)
3 days	7 (2.28%)	5 (2.55%)	2 (1.80%)
4 days	9 (2.93%)	4 (2.04%)	5 (4.50%)
5 days	7 (2.28%)	6 (3.06%)	1 (0.90%)
6 days	1 (0.33%)	1 (0.51%)	0 (0.00%)
7 days	4 (1.30%)	4 (2.04%)	0 (0.00%)
> 7 days	10 (3.26%)	5 (2.55%)	5 (4.50%)
Dk/Da	2 (0.65%)	0 (0.00%)	2 (1.80%)
N/A	243 (79.2%)	154 (78.6%)	89 (80.2%)
Has been vaccinated for COVID-19				1.000
Si	303 (98.7%)	193 (98.5%)	110 (99.1%)
No	3 (0.98%)	2 (1.02%)	1 (0.90%)
Dk/Da	1 (0.33%)	1 (0.51%)	0 (0.00%)
Number of vaccine’s doses				<0.001
One	18 (5.86%)	17 (8.67%)	1 (0.90%)
Two	92 (30.0%)	75 (38.3%)	17 (15.3%)
Three	194 (63.2%)	101 (51.5%)	93 (83.8%)
N/A	3 (0.98%)	3 (1.53%)	0 (0.00%)
Type of vaccine				<0.001
Pfizer	69 (22.5%)	44 (22.4%)	25 (22.5%)
Moderna	171 (55.7%)	91 (46.4%)	80 (72.1%)
Astra Zeneca	53 (17.3%)	53 (27.0%)	0 (0.00%)
Jansen	1 (0.33%)	1 (0.51%)	0 (0.00%)
Other	8 (2.61%)	4 (2.04%)	4 (3.60%)
Dk/Da	1 (0.33%)	0 (0.00%)	1 (0.90%)
N/A	4 (1.30%)	3 (1.53%)	1 (0.90%)

We detected 18 positive cases, including two cases which were identified as negative by the participants and as positive by the research team (Fig 2). The proportion of positive results was higher among teachers (7.3%) than health care professionals (3.6%) (p: 0.1959). Among positive participants there were: 11 teachers, three physicians, one nurse, two school administrative staff and one person without information.

We estimated a global prevalence of SARS-CoV-2 infection of 5.94% (CI 95%: 3.28, 8.6), being 3.6% (CI 95%: 0.14, 7.07) in health care professionals and 7.29% (CI 95%: 3.61, 10.97) in education professionals (P value: 0.2908).

Most participants (78.5%) with a positive result had symptoms compatible with COVID-19 and all of them but two, contacted their GP and isolated themselves after knowing the result (linkage to care rate: 88.9%). One was not possible to contact and the other one ignored the recommendations because she considered herself to be negative, although the research team read the result as positive and informed her of it.

Learnability

The majority of the participants (92.5%) found that the self-test was easy or very easy to use 99.7% successfully completed the test and, 88.9% did not need any help to perform the test no significant differences were observed between healthcare and education professionals. 93.5% agreed or strongly agreed with the statement “I trust that my interpretation of the result I obtained with the self-test is correct”, 81.6% of educators strongly agreed compared to 66.7% health professionals (P: 0.006) (Table 1). Two (0,6%) participants failed to read the test results.

Willingness

Most of participants (96.7%) agreed or strongly agreed with the statement “I would repeat the rapid SARS-CoV-2 antigen self-test in the future”, 90.3% of educators strongly agreed compared with 80.2% of health professionals (p: 0.021). The most preferred way to repeat the test was “do the self-test at home” (87.9%); and 99.3% would like the test to be available at their workplace, with no differences among health and education professionals (Table 2).

Table 2

Learability, willingness, suitability and satisfaction of the TESTATE COVID intervention adressed to health care and education professionals in Catalonia (Spain), N: 307.

December 2021-February 2022.

	All n(%)	Education professionals n(%)	Health care professionals n(%)
Learnability1	N = 307	N = 196	N = 111	p value
Test difficulty				0.479
Very easy	219 (71.3%)	145 (74.0%)	74 (66.7%)
Easy	65 (21.2%)	38 (19.4%)	27 (24.3%)
Neither easy or difficult	17 (5.5%)	10 (5.1%)	7 (6.3%)
Difficult	5 (1.6%)	2 (1.0%)	3 (2.7%)
Very difficult	0 (0.0%)	0 (0.0%)	0 (0.0%)
Dk/Da	1 (0.3%)	1 (0.5%)	0 (0.0%)
Have successfully completed the self-test				1.000
No	0 (0.0%)	0 (0.0%)	0 (0.0%)
Yes	306 (99.7%)	195 (99.5%)	111 (100%)
Dk/Da	1 (0.3%)	1 (0.5%)	0 (0.0%)
Needed help to perform the self-test				0.523
No	273 (88.9%)	171 (87.2%)	102 (91.9%)
Yes	33 (10.7%)	24 (12.2%)	9 (8.1%)
Dk/Da	1 (0.3%)	1 (0.5%)	0 (0.0%)
Trusting that the interpretation of the result obtained with the self-test is correct				0.006
Strongly agree	234 (76.2%)	160 (81.6%)	74 (66.7%)
Agree	53 (17.3%)	24 (12.2%)	29 (26.1%)
Neither agree nor disagree	9 (2.9%)	6 (3.1%)	3 (2.7%)
Disagree	7 (2.3%)	3 (1.5%)	4 (3.6%)
Strongly disagree	1 (0.3%)	0 (0.0%)	1 (0.9%)
Dk/Da	3 (1.0%)	3 (1.5%)	0 (0.0%)
Willingness 2
Would repeat the self-test in the future				0.021
Strongly agree	266 (86.6%)	177 (90.3%)	89 (80.2%)
Agree	31 (10.1%)	16 (8.2%)	15 (13.5%)
Neither agree nor disagree	3 (1.0%)	1 (0.5%)	2 (1.8%)
Disagree	3 (1.0%)	0 (0.0%)	3 (2.7%)
Strongly disagree	1 (0.3%)	0 (0.0%)	1 (0.9%)
Dk/Da	3 (1.0%)	2 (1.0)	1 (0.9%)
Preferred place to repeat the self-tets in the future				0.241
Health care centre	22 (7.2%)	18 (9.2%)	4 (3.6%)
Do the self-test at home	270 (87.9%)	170 (86.7%)	100 (90.1%)
Other	6 (1.9%)	3 (1.5%)	3 (2.7%)
Dk/Da	9 (2.6%)	5 (2.5%)	4 (3.6%)
Would like to have available self-tests at their workplace				0.595
Yes	304 (99.3%)	194 (99.5%)	110 (99.1%)
No	1 (0.33%)	1 (0.5%)	0 (0.0%)
Dk/Da	1 (0.33%)	0 (0.0%)	1 (0.9%)
Suitability 3
Confidence in the results obtained with the SARS-CoV-2 rapid antigen self-tests				0.236
Strongly agree	158 (51.5%)	105 (53.6%)	53 (47.7%)
Agree	117 (38.1%)	69 (35.2%)	48 (43.2%)
Neither agree nor disagree	18 (5.9%)	14 (7.1%)	4 (3.6%)
Disagree	10 (3.3%)	6 (3.1%)	4 (3.6%)
Strongly disagree	2 (0.6%)	0 (0.0%)	2 (1.8%)
Dk/Da	2 (0.6%)	2 (1.0%)	0 (0.0%)
Satisfaction 4
Test satisfaction				0.314
Very satisfied	236 (76.9%)	153 (78.1%)	83 (74.8%)
Satisfied	47 (15.3%)	26 (13.3%)	21 (18.9%)
Neither satisfied or unsatisfied	20 (6.51%)	15 (7.65%)	5 (4.50%)
Unsatisfied	3 (0.98%)	1 (0.51%)	2 (1.80%)
Very unsatisfied	0 (0.00%)	0 (0.00%)	0 (0.00%)
Dk/Da	1 (0.33%)	1 (0.51%)	0 (0.00%)
Would recommend the self-test to a friend				0.024
Strongly agree	246 (80.1%)	160 (81.6%)	86 (77.5%)
Agree	42 (13.7%)	24 (12.2%)	18 (16.2%)
Neither agree nor disagree	8 (2.6%)	8 (4.1%)	0 (0.0%)
Disagree	8 (2.6%)	3 (1.5%)	5 (4.5%)
Strongly disagree	1 (0.3%)	0 (0.0%)	1 (0.9%)
Dk/Da	2 (0.7%)	1 (0.5%)	1 (0.9%)
Advantges of the self-test
Self-test can improve security and protection of COVID-19 in the workplace	260 (84.7%)	170 (86.7%)	90 (81.1%)	0.247
Obtention of the results in a few minutes	262 (85.3%)	163 (83.2%)	99 (89.2%)	0.205
Privacy and confidentiality	111 (36.2%)	62 (31.6%)	49 (44.1%)	0.039
Convenience	258 (84.0%)	167 (85.2%)	91 (82.0%)	0.563
Test is free	195 (63.5%)	127 (64.8%)	68 (61.3%)	0.621
Do not need naso-pharyngeal swab	51 (16.6%)	28 (14.3%)	23 (20.7%)	0.195
Do not need to explain yourself to others	41 (13.4%)	22 (11.2%)	19 (17.1%)	0.199
Self-test contributes to normalize COVID-10 testing	131 (42.7%)	82 (41.8%)	49 (44.1%)	0.785
Self-tests allow taking control of our health	164 (53.4%)	108 (55.1%)	56 (50.5%)	0.505
Self-tests give more sense of security at the work place	168 (54.7%)	122 (62.2%)	46 (41.4%)	0.001
Other	3 (1.0%)	2 (1.0%)	1 (0.9%)	1.000
Disadvantges of the self-test
None	275 (89.6%)	173 (88.3%)	102 (91.9%)	0.421
Sensitivity and specificity lower than a PCR	17 (5.5%)	10 (5.1%)	7 (6.3%)	0.854
Having to interpretate the result by yourself	12 (3.9%)	6 (3.1%)	6 (5.4%)	0.363
The time for obtaining the result is too long	1 (0.3%)	0 (0.0%)	1 (0.9%)	0.362
Other	21 (6.8%)	10 (5.1%)	11 (9.9%)	0.171
Don’t know	16 (5.2%)	13 (6.6%)	3 (2.7%)	0.222
Don’t want to answer	3 (1.0%)	3 (1.5%)	0 (0.0%)	0.241

1. Learnability was defined as the ability of the participant to understand how to correctly perform the self-test and accurately read the test results.

2. Willingness was defined as the intention of participants to follow all the procedure.

3. Suitability was defined as participants’ belief that the test is relevant for their work and that test results are a true indication of the presence or absence of SARS-CoV-2 infection.

4. Satisfaction was described as feeling that being tested for COVID-19 through the TESTATE intervention was convenient and that it is a process they would experience again. Efficacy was defined as participants’ ability to make the effort and time to order the self-testing kit, perform the test, report the obtained result, as well as follow the linkage to care procedure if necessary.

Suitability

Most participants (89.6%) agreed or strongly agreed with the statement “I trust the result obtained with the self-test” (Table 2).

Satisfaction

92.2% of the participants answered that they were satisfied or very satisfied with the intervention; and 93.8% agreed or strongly agreed with the statement “I would recommend it to a friend” with 81.6% of educators strongly agreeing compared to 77.5% of health professionals (p:0.024). The advantages that were most identified were getting the result in a few minutes (85.3%) and the fact that the tests might improve safety and protection against COVID-19 at their workplace (84.7%); educators were more likely to identify “Self-tests give more sense of security at the workplace” as an advantage than health professionals (62.2% vs. 41.4%, p: 0.001); 89.6% did not identify any disadvantages.

Discussion

Testing is a critical component of the overall prevention and control strategy for the COVID-19 pandemic [12]. Nevertheless, apart from contact tracing strategies, screening of key populations implies many logistical and operational challenges, including the necessity of periodic testing in periods of high incidence (ex. twice a week) in order to be effective [2]. Highly sensitive self-tests are cheap, simple, rapid tests and that can enable high frequency regimens that will capture most infections while they are still infectious.

Uploading the pictures of the results online contributed to better traceability of positives and this could improve the ability to break the epidemiological chain.

Although the study used an opportunistic sample that is not representative of the healthcare and education professionals of the region, we demonstrated that the TESTA’T COVID intervention is feasible. We provided an in-depth account of acceptability and usability of an online screening strategy based on antigen self-tests for COVID-19 addressed to health care and education professionals in Catalonia. Our study showed high feasibility of the intervention both in healthcare and education professionals, although education professionals presented higher learnability with higher level of trust in having a correct interpretation of the obtained results; and, higher willingness to repeat the self-test in the future and to recommend it to a friend. In the event of a possible consolidation of the pilot intervention, the implementation of campaigns to increase the level of trust and acceptability of self-tests by healthcare professionals should be considered.

High proportion of participants tested positive (88.9%) were able to correctly read their result, similarly to previous studies [13]. Errors might be reduced by refinement of the instructions provided.

Apart from showing a high feasibility our pilot intervention showed high efficacy in terms of number of tests requested, number of correctly uploaded picture of the result, answered surveys, and positivity and linkage to care rates). Linkage to care is challenging in self-sampling strategies, however we obtained high percentages of linkage to care (88.9%).

This is the first time this was done in Spain, and during the peak of the 6th wave caused by the Omicron variant. Our pilot intervention has been proved feasible and has the potential for frequent and extensive testing. The generated information on acceptability and usability, as well as positivity and linkage to acre rates, will be crucial to better define tailored screening strategies addressed to specific key populations, particularly during peaks of high community transmission of SARS-CoV-2 and eventually other respiratory transmitted agents.

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26 May 2022

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Please confirm that this does not alter your adherence to all PLOS ONE policies on sharing data and materials, by including the following statement: "This does not alter our adherence to  PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests).  If there are restrictions on sharing of data and/or materials, please state these. Please note that we cannot proceed with consideration of your article until this information has been declared.

Please include your updated Competing Interests statement in your cover letter; we will change the online submission form on your behalf.

4. We note that you have indicated that data from this study are available upon request. PLOS only allows data to be available upon request if there are legal or ethical restrictions on sharing data publicly. For information on unacceptable data access restrictions, please see http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions.

In your revised cover letter, please address the following prompts:

a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent.

b) If there are no restrictions, please upload the minimal anonymized data set necessary to replicate your study findings as either Supporting Information files or to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. Please see http://www.bmj.com/content/340/bmj.c181.long for guidelines on how to de-identify and prepare clinical data for publication. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories.

We will update your Data Availability statement on your behalf to reflect the information you provide.

5. Please include your tables as part of your main manuscript and remove the individual files. Please note that supplementary tables (should remain/ be uploaded) as separate "supporting information" files.

[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: Partly

Reviewer #2: Partly

**********

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

Reviewer #1: I Don't Know

Reviewer #2: I Don't Know

**********

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

Reviewer #2: No

**********

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: No

Reviewer #2: 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: the respected authors presented a good idea that would add to the available methods of screening. But it is poorly presented , many changes are needed to be suitable for publication.

abstract: the aim is not properly formulated. changes will be needed based on the next points.

introduction: what is the knowledge gap that you are trying to cross-over.

the rationale is missed.

the aim of the study is vague and not fulfilled in the manuscript. you may change it to be:"to assess the feasibility of the TESTATE COVID screening strategy among.......".

Methods:

Add a figure to illustrate the flow of recruitment process.

move the illustration/definition of the framework components to the methods section.

what are your study outcomes?

The discussion is very confusing, the term "screening" is not properly used. the authors need to clarify what is their target. you may recommend using the kit based on your findings, but in the current status I can't get what is your target.

you need to discuss the main findings, the difference between your 2 groups, and so on ...

The conclusion and recommendation are deficient.

Reviewer #2: The authors have done a good job/

Here are my comments:

Introduction:

- More data from the literature should be mentioned to show the complexity of detecting COVID cases, the use of the antigen tests, and their limitations.

- The references used are very limited, more evidence should be added to support the study's claim.

Methodology:

- The interpretation of test results by the professional team is not clear.

- Nothing was mentioned regarding the statistical analysis of data.

- More data regarding inclusion criteria and procedures for collecting the survey data are needed.

- The used framework for evaluation is not well explained.

Results:

- Adding one or two figures illustrating the data mentioned, especially those from the survey would benefit the presentation of data

- The results should be statistically analyzed and presented in the results section

Discussion:

- The discussion section should include more previous studies that are comparable or related to the current study.

- The part of the evaluation should be explained more with relevance to the above-mentioned framework to be able to give a conclusion on the overall feasibility.

Conclusion:

More conclusions of the study should be added at the end

**********

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: Yes: rehab Hosny El-Sokkary

Reviewer #2: 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.

28 Jul 2022

PONE-D-22-12378

Feasibility of an online antigen self-testing strategy for SARS-CoV-2 addressed to health care and education professionals in Catalonia (Spain). The TESTA’T- COVID Project

COMMENTS TO THE AUTHORS

ACADEMIC EDITOR:

Respected authors your manuscript is good. However; your research manuscript needs great attention from your side to reach to required level for publishing specially regarding; the objectives for this study which need to be clear and specific.

Answer: Following the recommendations of the Editor and the reviewers, the objectives have been re-written.

The method section has been completed and re-organized in a proper scientific way.

Answer:

The results; be sure that your table is inserted within the manuscript and not in the attached other files.

Answer: The tables have been inserted within the manuscript.

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

Answer:

2. Please provide additional details regarding participant consent. In the ethics statement in the Methods and online submission information, please ensure that you have specified what type you obtained (for instance, written or verbal, and if verbal, how it was documented and witnessed). If your study included minors, state whether you obtained consent from parents or guardians. If the need for consent was waived by the ethics committee, please include this information.

Answer: Additional details regarding the informed consent have been included in the new version of the manuscript.

3. Thank you for stating the following in the Competing Interests section:

"I have read the journal's policy and the authors of this manuscript have the following competing interests: Abbot Laboratories provided the tests for the study for free"

Please confirm that this does not alter your adherence to all PLOS ONE policies on sharing data and materials, by including the following statement: "This does not alter our adherence to PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests). If there are restrictions on sharing of data and/or materials, please state these. Please note that we cannot proceed with consideration of your article until this information has been declared.

Please include your updated Competing Interests statement in your cover letter; we will change the online submission form on your behalf.

Answer: The updated Competing Interests statement has been included in the Competing Interests section and in the cover letter.

4. We note that you have indicated that data from this study are available upon request. PLOS only allows data to be available upon request if there are legal or ethical restrictions on sharing data publicly. For information on unacceptable data access restrictions, please see http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions.

In your revised cover letter, please address the following prompts:

a) If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially identifying or sensitive patient information) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent.

b) If there are no restrictions, please upload the minimal anonymized data set necessary to replicate your study findings as either Supporting Information files or to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. Please see http://www.bmj.com/content/340/bmj.c181.long for guidelines on how to de-identify and prepare clinical data for publication. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories.

We will update your Data Availability statement on your behalf to reflect the information you provide.

Answer: In the informed consent approved by the Ethical Committee of the Germans Trias i Pujol Hospital (PI-20-368) it was included the following statement: No sharing data with third party is planned. For this reason, we understand we are not able to share data of the included participants.

5. Please include your tables as part of your main manuscript and remove the individual files. Please note that supplementary tables (should remain/ be uploaded) as separate "supporting information" files.

Answer: Done.

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: Partly

Reviewer #2: Partly

Answer: We re-wrote the manuscript to solve this issue.

________________________________________

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

Reviewer #1: I Don't Know

Reviewer #2: I Don't Know

Answer: We further explained the statistical data analysis performed in the new version of the manuscript.

________________________________________

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

Reviewer #2: No

Answer: In the informed consent approved by the Ethical Committee of the Germans Trias i Pujol Hospital (PI-20-368) it was included the following statement: No sharing data with third party is planned. For this reason, we understand we are not able to share data of the included participants.

________________________________________

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: No

Reviewer #2: Yes

Answer: We re-wrote the manuscript to solve this issue.

________________________________________

5. Review Comments to the Author

Reviewer #1: the respected authors presented a good idea that would add to the available methods of screening. But it is poorly presented, many changes are needed to be suitable for publication.

Abstract: the aim is not properly formulated. Changes will be needed based on the next points.

Answer: Following the recommendation of the reviewer, the aim has been reformulated in the abstract and in the introduction section.

Introduction: what is the knowledge gap that you are trying to cross-over.

Answer: The introduction section has been extended.

The rationale is missed.

Answer: The rationale has been included in the introduction section.

The aim of the study is vague and not fulfilled in the manuscript. You may change it to be:"to assess the feasibility of the TESTATE COVID screening strategy among.......".

Answer: Following the recommendation of the reviewer, the aim has been reformulated in the abstract and in the introduction section.

Methods:

Add a figure to illustrate the flow of recruitment process.

Answer: Done. See Figure 2.

Move the illustration/definition of the framework components to the methods section.

Answer: Done. A figure of the framework components has been included in the methods section and the definition of each component has been added in the text.

What are your study outcomes?

Answer: An explanation of what are the study outcomes has been included in the methods section.

The discussion is very confusing, the term "screening" is not properly used. the authors need to clarify what is their target. you may recommend using the kit based on your findings, but in the current status I can't get what is your target.

you need to discuss the main findings, the difference between your 2 groups, and so on ...

Answer: We clarified and extended the Discussion section. We agreed with the reviewer that it was not clear enough. We also agreed that the term screening was not properly used and we correct this issue.

The conclusion and recommendation are deficient.

Answer: We included more conclusions and recommendations in the Discussion section.

Reviewer #2: The authors have done a good job/

Here are my comments:

Introduction:

- More data from the literature should be mentioned to show the complexity of detecting COVID cases, the use of the antigen tests, and their limitations.

Answer: The introduction section has been extended to add more information from the literature to show the complexity of detecting COVID cases, the use of the antigen tests, and their limitations.

- The references used are very limited, more evidence should be added to support the study's claim.

Answer: The introduction section has been extended to add more evidence.

Methodology:

- The interpretation of test results by the professional team is not clear.

Answer: We added an explanation about the procedure in the Methods section.

- Nothing was mentioned regarding the statistical analysis of data.

Answer: An explanation of the statistical analysis of data has been added in the Methodology section of the new version of the manuscript.

- More data regarding inclusion criteria and procedures for collecting the survey data are needed.

Answer: An explanation of the inclusion criteria has been added in the Methodology section of the new version of the manuscript

- The used framework for evaluation is not well explained.

Answer: An explanation of the framework used for the evaluation has been added in the Methodology section of the new version of the manuscript

Results:

- Adding one or two figures illustrating the data mentioned, especially those from the survey would benefit the presentation of data

Answer: An extra table and two figures have been included in the new version of the manuscript.

- The results should be statistically analyzed and presented in the results section

Answer: The results section has been modified. We added the p value and the interval of confidence of data presented.

Discussion:

- The discussion section should include more previous studies that are comparable or related to the current study.

Answer: Little information is available on pilot intervention that offer self-tests to detect SARS-CoV-2 infection. Some studies have been included in the introduction and the discussion.

- The part of the evaluation should be explained more with relevance to the above-mentioned framework to be able to give a conclusion on the overall feasibility.

Answer: The part of the evaluation has been explained more and we included an overall conclusion of the feasibility.

Conclusion:

More conclusions of the study should be added at the end.

Answer: More conclusions have been included in the Discussion section.

________________________________________

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: Yes: rehab Hosny El-Sokkary

Reviewer #2: 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.

Submitted filename: Response_to_reviewers_29062022.docx

Click here for additional data file.

29 Aug 2022

8 Sep 2022

PONE-D-22-12378R1

Feasibility of an online antigen self-testing strategy for SARS-CoV-2 addressed to health care and education professionals in Catalonia (Spain). The TESTA’T- COVID Project

PLOS ONE

Dear Dr. Agustí,

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.

==============================

ACADEMIC EDITOR:

Dear authors you did a great job, only few changes need to bee done

- the objective in the abstract must be as at the end of the introduction

- in the method section ; it needs to be organized under subheadings to make your work more clear and please write them in order as; study design, study sitting and timing, study population, sampling and sample size, tools of data collection, study outcomes data mangement, ethical consideration.

Answer: The authors have included the suggested changes in the reviewed version of the manuscript.

==============================

Please submit your revised manuscript by Oct 13 2022 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'. Done.

• 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'. Done

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

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. Not necessary.

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: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Omnia Samir El Seifi, Professor

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. Done

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

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

2. 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: (No Response)

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

Reviewer #1: (No Response)

4. 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: (No Response)

5. 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: (No Response)

6. 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: Thanks for addressing all raised concern

only one is left: write the aim in the abstract section like that mentioned in the text.

Answer: We have included the aim in the abstract section like that mentioned in the text.

7. 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: Yes: rehab Hosny El-Sokkary

Submitted filename: Response_to_reviewers_29082022.docx

Click here for additional data file.

9 Sep 2022

Feasibility of an online antigen self-testing strategy for SARS-CoV-2 addressed to health care and education professionals in Catalonia (Spain). The TESTA’T- COVID Project

PONE-D-22-12378R2

Dear Dr. Agustí,

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,

Omnia Samir El Seifi, Professor

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

14 Sep 2022

PONE-D-22-12378R2

Feasibility of an online antigen self-testing strategy for SARS-CoV-2 addressed to health care and education professionals in Catalonia (Spain). The TESTA’T- COVID Project.

Dear Dr. Agustí:

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

Professor Omnia Samir El Seifi

Academic Editor

PLOS ONE