Domestic and peridomestic risk factors associated with transmission of cutaneous leishmaniasis in three hypo endemic, endemic, and hyper endemic areas: A randomized epidemiological study.

BACKGROUND: Leishmaniasis is an infection caused by leishmania protozoa. Knowledge about health effects associated with environment situation and human behavior in national and local levels seems to be very necessary.
MATERIALS AND METHODS: This cross-sectional case-control study was carried out in three adjacent counties of Isfahan province in Iran. Data were collected by face-to-face interviewing and recorded structured questionnaire. Statistical analysis was performed using Chi-square test and logistic. P < 0.05 was considered as significant.
RESULTS: The economic level had significant association with cutaneous leishmaniasis (CL) transmission (P < 0.05). However, there was no significant association between existence of food storage and transmission of CL. We, however, found significant reduction of CL transmission following use of insect control measures (P < 0.05). The odds ratio for peridomestic transmission was 0.420 for houses that weren't round with any old or ruined houses.
CONCLUSION: We conclude that among aforementioned risk factors, the impact of peridomestic factors is stronger in CL transmission when compared with domestic and behavioral factors.

INTRODUCTION

Leishmaniasis is an infection caused by special protozoa named leishmania protozoa, and are usually transmitted by the bite of phlebotomine sand flies.[1] Leishmaniasis is endemic in 88 countries nearly throughout all worlds. Cutaneous leishmaniasis (CL) occurs in the new world and in the old world. In the old world, the disease is primarily caused by Leishmania tropica in urban areas (dry type) and leishmania major (wet type) in dry desert areas.[2] CL is still considered and growing as an important health problem and concern in especially the Mediterranean region, some countries of Africa, and almost all countries of the Middle East, including Iran.[3456] The prevalence of infection is high in some provinces of Iran such as Isfahan. Isfahan is a well-known endemic area of zoonotic cutaneous leishmaniasis. In north east of Isfahan, the disease incidence is high.[78] Interventions for decreasing sand fly abundances and biting rates in domestic and peri-domestic transmission foci, may reduce outbreak. In a study by Campbell-Lendrum et al., it was shown the significantly decrease in CL incidence in protected houses during the trial.[9] Also some activities such as working or helping in an agricultural area or water collection could be associated with an increased risk of CL.[10] Because most time of people are spent in residential and work environment a knowledge about health effects associated with environment situation and human behavior in seems to be necessary. This study is designed to determine association of domestic and extra domestic characteristics, human behaviors and occupational activities with CL transmission.

MATERIALS AND METHODS

This study was carried out in three adjacent counties of Isfahan province: Borkhar, Malekshahr and Isfahan counties, which are hyper endemic, endemic, and hypo endemic for leishmanisis, respectively.

This was a cross-sectional case-control study that cases and controls were matched by sex, age, resident duration and census tract.

Study cases were selected from patients with positive direct smear for CL and from the three areas of Isfahan province during 2007-2008 and have had positive direct smear for leishmaniasis parasite or had positive clinical approve from skin specialist and if were positive, they were created record.

Controls consisted subjects living in the study areas and had no clinical signs of CL or its scar and were selected among residents of households in the same patients’ census tract.

Sample size was calculated to be 200 for each group using the following formula (with α = 0.05 p1 = 0. 5 p2 = 0. 5 d = 0.1).

N = [z (1 − α/2)] ² [p1 (1 − p1) + p2 (1 − p2)]/d² N = 200 per group.

Sample population was selected by simple randomization technique according to filed patient record numbers. First, all of residential addresses of patients referred to skin diseases and leishmaniasis research center were coded in SPSS software (SPSS Inc. 233 South Wacker Drive, 11th Floor Chicago, IL 60606-6412), then study area selected codes were evaluated in ratio followed by randomized, in order to these patient addresses, they were extracted according to their record numbers. If the chosen patient record was not eligible for study the next ones were evaluated for eligibility.

Data collected by face to face interviewing in a structured questionnaire applied by a team of trained primary health workers. Interviewers observed domestic and peridomestic environment of cases and controls and filled the questionnaires.

The questionnaire contained several sections including:

Sociodemographic characteristics: Age, sex, level of education, economic level, address code, and duration of residency

Domestic (indoor) factors: Family size, number of rooms, construction materials, type of main entrance, food storage, domestic animals, garbage collection, type of floor and roof, preventive activities (insecticide spraying)

Peridomestic factors: Presence and distance to any construction, location of garbage, animal sheds, sources of water, roadway and agricultural areas around the houses

Human behavior: Sleep location in summer and spring, swimming and occupational activities and dealing with soil and animals.

Its validity and reliability were confirmed through consulting with a panel of experts (hygiene professionals and statisticians) and pilot study performance.

Statistical analysis was conducted using Chi-square test for qualitative (categorized) variables for finding the significant variables related to leishmaniasis involving, and for some variables associated with leishmanisis, a multivariate analysis (logistic regression) was conducted to detect interactions between variables. This binary logistic analysis performed by forward conditional method defined categorical variables with simple contrast and with selection of first category as reference category. P < 0.05 was assumed as significant.

RESULTS

The distribution of cases and controls did not differ by age, sex, duration of residency, and census tract. Overall the ratio of cases-controls was 1. The lowest frequency of age group was 1-3 years (4%), and highest was 18-40 years old (43.3%).

Sex of total population in this study included 60.3% of the patients were male and 39.8% of them were females and maximum frequency of residential duration range was in 5 or <5 years.

In other sociodemographic characteristics, the level of education and the type of endemic area weren’t significant in related to CL transmission (P > 0.05) and the economic level was significant, which cases included 17% high, 54% medium, 29% low economic level, and controls included 8.5% high, 62% medium, 29.5% low economic level (P = 0.03). The risk of CL transmission related to economic level is shown in Table 1. High economic level became reference category and the odds ratio (ORs) associated with this variable were statistically significant. The ORs of the association between medium and low compared with high economic levels showed that ratio of low level (2.034) for CL transmission was less than medium level (2.296).

Table 1

Risk of CL transmission related to economic level

Factors that were significantly associated with domestic (indoor) and peridomestic leishmaniasis transmission (P < 0.05) are shown in Table 2.

Table 2

Significant domestic (indoor) and peridomestic factors associated with CL transmission

Some domestic variables contributed significantly in the multivariate analysis remained [Table 3]: House measurement (square meter), type of floor, insect control by members of the household, and food storage. In houses measurement variable, we can be noted that cases houses were wider than controls. The risk of CL transmission related to house measurement between 100 and 200 m² (0.589) was more than other categories compared with 100 m² or <100 m² house measurement as reference category. In food storage variable, the risk was 0.247 and also in insect control variable was 0.120 in those who didn’t have any storage and insect control compared with those who have had these variables. Furthermore, in the categories of floor types variable, the risk of CL transmission related to floors, which made up mosaic and gatch (1.033) was more than ceramic category compared with floors made up sun-dried bricks.

Table 3

Risk of CL transmission (ORs) related to domestic (indoor) factors with 95% CIs

Among peridomestic factors that were suitable for multivariate analysis, four factors were significantly associated with CL [Table 4]. The ORs of peridomestic transmission were 0.420 for houses that didn’t round with any old or ruined houses, but it was different for peridomestic animal sheds or kennels and water sources. The risk of peridomestic roadways >50 meter was higher other categories related to this variable.

Table 4

Risk of CL transmission (ORs) related to peridomestic factors with 95% CIs

In human behavior factors, job and professional behavior have significant affects on CL transmission [Table 5].

Table 5

Significant professional behavior factors associated with CL transmission

Variables in this section in the equation for OR comparing, were bite exposure in job and involvement with soil [Table 6]. Individuals who didn’t have any bite exposure had higher risk of CL (OR = 10.314) as compared with those who didn’t involve with soil in their jobs (OR = 2.133).

Table 6

Risk of CL transmission (ORs) related to professional behavior factors with 95% CIs

DISCUSSION

This study has shown the impact of economic level, which the risk of CL transmission for low and medium economic level was more than high level. In domestic factors, it was indicated that cases houses had higher measurement than controls. However, it wasn’t consistent with economic level and it was possibly because of other criteria consideration (such as income level). Although floors and plinths of houses, soil at the edges and at the bases of stone walls are good sites for the sandflies breeding,[11] but in this study floors made up sun-dried bricks weren’t strongly associated with CL transmission. This isn’t interpreted for insect control, that there was relationship between insect control (spray implementation) for CL prevention.

In a study by Yadon et al., it was also shown that the adjusted OR of the association between products stored with no-storage showed a small decrease compared with the crude OR.[10] This is consistent with our study.

Among peridomestic factors, presence of old or ruined houses and roadway around the house were most associated with CL transmission.

The importance of domestic transmission is reconsideration of the view that CL can be considered occupational diseases since they are directly related to professional activities.[12] In spite, our results showed that the percent of jobs that involve with soils, animals and farms and also drivers in cases were more than controls. However, it was opposite for impact of these variables in risk of CL transmission that the ORs of involvement with soil and bite exposure in job were very less than no involvement with soil or no bite exposure.

These results illustrate the need for the peridomestic prevention of CL transmission in these study areas. We conclude that among aforementioned risk factors, the impact of peridomestic factors is stronger in CL transmission as compared with domestic and behavioral factors. Hence, according to many studies investigated these factors,[910131415] we recommend to select and compare these factors in other areas specially two type of urban and rural areas.

AUTHORS CONTRIBUTION

MAN contributed in the work, conducting the study, revising the draft, approval of the final version of the manuscript, and agreed for all aspects of the work. SMH contributed in the conception of the work, revising the draft, approval of the final version of the manuscript, and agreed for all aspects of the work. AH contributed in the conception of the work, conducting the study, drafting and revising the draft, approval of the final version of the manuscript, and agreed for all aspects of the work. LSB contributed in the work, revising the draft, approval of the final version of the manuscript, and agreed for all aspects of the work. AHS contributed in the work, revising the draft, approval of the final version of the manuscript, and agreed for all aspects of the work.