Prevalence, risk factors and health consequences of soil-transmitted helminth infection on the Bijagos Islands, Guinea Bissau: A community-wide cross-sectional study

Author summary To date, the overall aim of the WHO policy of STH control through periodic mass-drug administration (MDA) has been morbidity control through a reduction in infection intensity in school-aged children. The main limitation of this approach is the rapid re-infection rate, both from the environment in areas with poor sanitation, and the persistent reservoir in adults who are not included in the MDA programme. As a consequence of this limitation, there have been calls to change the overall aim from morbidity control to the elimination of STH infection altogether by breaking the transmission cycle through community-wide deworming. However, there is a dearth of epidemiological data pertaining to adults in relation to STH and in addition, most surveys exclude the helminth Strongyloides stercoralis, due to limitations of the diagnostic methods used. Our study aims to provide up-to-date epidemiological data of STH prevalence, individual and household risk-factors for infection and the association with anaemia and malnutrition in children under 5 years. From 396 participants who provided a stool sample, we found a high prevalence of STH infection, predominantly the hookworm Ancylostoma duodenale, across all age-groups and both sexes. There was a clear association between STH infection and open defaecation in this study, with use of a protected pit latrine protective against infection. There were high rates of anaemia and malnutrition which had no statistically significant association with STH infection, and are likely multifactorial. This study uncovered an ongoing reservoir of STH infection despite high coverage with mebendazole MDA, high rates of morbidity alongside the STH infection and a clear association between STH infection and inadequate sanitation. This reflects the need for further interventional research to assess the optimum strategy to alleviate morbidity and break the STH transmission cycle in this population. Soil-transmitted helminths (STH) are endemic and widespread across Sub-Saharan Africa. A community wide soil-transmitted helminth (STH) prevalence survey was performed on the island of Bubaque in Guinea-Bissau using both Kato-katz microscopy and qPCR methodology. Predictors of infection and morbidity indicators were identified using multivariable logistic regression, and diagnostic methods were compared using k statistics. Among 396 participants, prevalence of STH by microscopy was 23.2%, hookworm was the only species identified by this method and the mean infection intensity was 312 eggs per gram. qPCR analysis revealed an overall prevalence of any STH infection of 47.3%, with the majority A. duodenale (32.3%), followed by N. americanus (15.01%) and S. stercoralis (13.2%). A. lumbricoides, and T. trichiura infections were negligible, with a prevalence of 0.25% each. Agreement between diagnostic tests was k = 0.22, interpreted as fair agreement, and infection intensity measured by both methods was only minimally correlated (R-s = -0.03). STH infection overall was more common in females and adults aged 31-40. STH infection was associated with open defaecation, low socio-economic status and further distance to a water-source. The prevalence of anaemia (defined as a binary outcome by the WHO standards for age and sex) was 69.1%, and 44.2% of children were malnourished according to WHO child growth standards. Hookworm infection intensity by faecal egg count showed no statistically significant association with age (R-s 0.06) but S. Stercoralis infection intensity by qPCR cycle threshold was higher in pre-school aged children (R-s = 0.30, p-value 0.03) There was no statistically significant association between STH infection and anaemia (OR 1.0 p = 0.8), stunting (OR 1.9, p-value 0.5) and wasting (OR 2.0, p-value 0.2) in children. This study reveals a persistent reservoir of STH infection across the community, with high rates of anaemia and malnutrition, despite high-coverage of mebendazole mass-drug administration in pre-school children. This reflects the need for a new strategy to soil-transmitted helminth control, to reduce infections and ultimately eliminate transmission.