Study design, area and population
A community based cross-sectional study was carried out in PSAC living in Panamasso, from February to March 2020. Panamasso is a village located in Dafra District at 30 kms from Bobo-Dioulasso, the second largest city of Burkina Faso, at 11°23'0'' North and 4°12'0'' West. This locality is located on the edge of one of the tributaries of the Mouhoun River. It is an area with high humidity from May to October and sheltering a pond, thus providing an environment suitable for growing of intermediate snail hosts of S. mansoni i.e. Biomphalaria pfeifferi (21). Panamasso had 600 households with 4,403 inhabitants in 2019. The pond is the main source of water for domestic activities (drinking, cooking, washing, bathing, and recreation) despite well-functioning water supplies. This village is the only sentinel site of the NSCP to record in 2013 and in 2016 high prevalence of S. mansoni infection in SAC with respective values of 39.1% and 26.2 % (23,24). PSAC who were under the age of six years old were the source population. PSAC who had been living in Panamasso for at least 6 months before the study began, whose parents/guardians provided written informed consent, and who had no history of having been treated with praziquantel and anti-helminthic drug in the past 6 months were included. Children who did not provide any stool sample during the survey were not included.
Sample size and sampling technique
Sample size was calculed upon a S. mansoni infection prevalence of 26.2 % previoulsy reported in SAC from Panamasso (24), a relative precision of 8 %, for alpha = 0.05, and using design effect of two. It was estimated to 230 participants accounting for 10% of parent’s refusal. A multiple-stage sampling procedure was used to randomly select 300 households from a list of the total households of the study village, then all eligible PSAC were included up to the sample size was reached.
Field data collection
A community information meeting was organized by the research team before the beginning of study. Then, an individual structured questionnaire was administered to the PSAC’s parents or guardians after having obtained their informed consent. Thereafter, sociodemographic data of the PSAC and their parents’ sociodemographic data and level of knowledge about schistosomiasis, and water contact data were collected. Water contact was assessed by inquiring on child’s history of going to the pond, child’s habit of swimming in the pond, frequency swimming habit of child in the pond per week (i.e. the reported number of days in the week that the child had been to the pond), and period of swimming in the pond.
Sample collection and laboratory procedures
Single stool and urine samples were collected in separate clean containers from each PSAC and processed at the Laboratory of Parasitology of Centre MURAZ.
One Kato-Katz thick smear was prepared from each stool sample using a template holding
41.7 mg of stool sample (26). The slides were left for 24 hours to clear for easy visualization of S. mansoni eggs before being examined. Infection intensity of S. mansoni was estimated by multiplying the total number of eggs counted by 24, which was given as the eggs per gram (epg) of faeces and classified as light, moderate and heavy per the threshold set by the World health organization (27). Two independent lab technicians examined each slide and any resulting discrepancies were resolved by the senior parasitologist. As a quality control check, 20% of all positive and negative slides were randomly chosen and re-read by the senior parasitologist in order to confirm positive or negative results.
Formol ether concentration technique (FEC)
After having diluted a small amount of stool (about 2 g) in 7 mL of 10% salt formalin solution (mixture of 100 mL of pure formalin, 900 mL of distilled water and 8.5 g of sodium), the mixture was sieved in a centrifuge tube to remove large debris and 3 mL of ether was added thereto. The mixture was stirred vigorously for 30 seconds and centrifuged at 2,000 rpm for 2 minutes. Then, the supernatant was discarded and the pellet was plated, using a pipette, between slide and coverslip with lugol and read on 10x and 40x objectives (28).
Qualitative examination for S. mansoni circulating cathodic Antigens(CCA)
All urine samples were tested for S. mansoni CCA using a commercially available point-of-care (POC-CCA) cassette test (Batch numbers 191031120, ICT INTERNATIONAL, Noordhoek, South Africa) performed at room temperature according to the manufacturer’s instructions on the day of the sample collection. Briefly, two drops of urine were added to the well of the testing cassette and allowed to absorb. The test results were read visually 20 minutes later. In cases when the control bands did not develop, the test was considered as invalid. Invalid tests were repeated using the same urine sample. Valid tests were scored as negative or positive. Trace (weak band) was also considered as positive (29). All the tests were read independently by two lab technicians, and in case of discordant results, the senior parasitologist examined it until an agreement was reached.
Urine centrifugation method
Briefly, 10 mL urine were centrifuged at 5,000 rpm for 5 minutes. Then, the supernatant was discarded and the pellet was plated, using a pipette, between slide and coverslip with lugol and read on 10x and 40x objectives. This method was used to check for S. haematobium infection.
This study was approved by the institutional ethical committee from Centre MURAZ (ref 2019-66/MS/SG/INSP/DG/CEI). Following an explanation of the purpose, the benefits and the possible risks of the study, written consent was obtained from PSAC’ parents/guardians. Children who were positive for S. mansoni were treated free of charge with praziquantel. All the information obtained from the PSAC and their parents was treated as private and confidential and the records were stored in a locked cabinet.
Data were double entered using Microsoft Excel 2013, then cleaned and analyzed with Stata 12 software (Stata Corp., College Station, Texas, USA).
S. mansoni infection was defined as any positive test result irrespective of the laboratory methods used. Pearson's chi-square test or Fisher's exact test was used to compare proportions between groups. Geometric means of intensity infection (GMI) and their 95% confidence intervals (95% CI) were estimated. Log-transformed means eggs count were compared between groups using parametric tests (Student or ANOVA) or nonparametric tests (Wilcoxon or Kruskal-Wallis), where appropriate. The Bonferroni test was used when the ANOVA test was statistically significant.
Potential risk factors for S. mansoni infection were screened through univariable logistic regressions when P-value < 0.2. Multivariable logistic regression model was built using a stepwise backward method by including in the model all independent variables of the univariable analysis with a P-value < 0.2. The results were presented with odds ratios (OR) and their 95% CI. Statistical significance was set for a P-value < 0.05.