Spatial analysis of diarrhoea and environmental risk factors in an urban context in Senegal, West Africa

Background: Diarrhoeal diseases continue to be a major public health concern globally, associated with high childhood mortality and morbidity, particularly in low- and middle-income countries (LMICs). Although the number of deaths due to diarrhoea decreased considerably over the past 25 years, morbidity has declined only moderately. In 2015, diarrhoea was responsible for nearly half a million deaths (9%) among children under the age of 5 years. Most of the diarrhoea-related deaths were attributable to unsafe water, inadequate sanitation and lack of hygiene. In 2015, an estimated, 844 million and 2.3 billion people around the world still lack access to basic drinking water service and sanitation facilities, respectively, mainly in LMICs, and particularly in sub-Saharan Africa.
In Senegal, diarrhoea is the leading cause of childhood deaths and about 14% of the burdens, as expressed by of disability-adjusted life years (DALYs), were due to diarrhoeal diseases in children below the age of 5 years.
While diarrhoea is among the leading infectious diseases, most studies were conducted in capital cities or rural areas, while little information is available for “secondary cities” so-called “medium-sized cities”. Secondary cities in many African countries, including Senegal, are faced with a lack of epidemiological data at small scale (e.g. neighbourhood level): prevalence and incidence, aetiologies and exposure factors. Data at small scale, as well as spatially and explicit assessment of disease risk like diarrhoea are lacking in secondary cities for effective guidance and planning of interventions. Against this background, data at small scale are needed in such urban settings to establish the local epidemiology and implement appropriate preventive measures. To address this research gap, the work undertaken in the current PhD thesis was conducted in a context of secondary cities, characterized by rapid urbanization, where control of infectious diseases, including diarrhoea, is a challenge.
Goal and objectives: The overarching goal of this PhD thesis was to provide disaggregated evidence on diarrhoeal diseases prevalence and incidence among children under the age of 5 years, including risk factors, in order to improve the control of the disease through the implementation of targeted preventive measures in the secondary city of Mbour, located in the south-western part of Senegal. To achieve this goal, the PhD thesis pursued the following five specific objectives: (i) to provide an overview of the urbanization trends of the secondary city of Mbour and its effects on water supply, sanitation, wastewater and solid waste management systems; (ii) to determine the prevalence of diarrhoea among children under the age of 5 and associated risk factors in four different zones of the city;
(iii) to investigate the association between childhood diarrhoeal incidence and climatic factors, such as temperature and rainfall; (iv) to describe the spatial pattern of diarrhoeal disease risk and to estimate the spatially varying association between diarrhoea risk and potential risk factors or covariates; and (v) to assess the knowledge and management practice of diarrhoea among mothers and caregivers of enrolled children.
Methods: The methodology developed in this thesis combines several types of data collection and analytical approaches. We collected data from readily available secondary sources from local services (e.g. routine health facility data on diarrhoeal incidence, demographics and mapping data), available remote sensing sources for the climatic data (e.g. temperature and rainfall), and obtained primary data from combined field surveys conducted in Mbour: cross-sectional epidemiological household surveys, drinking water sampling and analysis, mapping of environmental risk factors at city and household level and direct observations.
Two cross-sectional household surveys were conducted in Mbour. The first survey was carried out in the dry season, between February and March 2014 among 600 children under the age of 5 years in eight randomly selected neighbourhoods located in four urban zones in Mbour namely: (i) Urban Central Area (UCA); (ii) Peri-Central Area (PCA); (iii) North Peripheral Area (NPA); and (iv) South Peripheral Area (SPA). The second survey was conducted in the rainy season between September and October 2016 among 800 children and covered all 25 neighbourhoods of the city, including the eight neighbourhoods sampled in the first survey. In both surveys, households were randomly selected using a spatial multi-stage cluster sampling approach, adopted within each zone and neighbourhood. The presence of a mother with at least one child under the age of 5 years was the primary household inclusion criterion. Questionnaires were administered to children’s parents/ caregivers to assess basic household socioeconomic and demographic characteristics and water, sanitation and hygiene (WASH) conditions, and to determine their knowledge, attitudes and management practices of diarrhoea (KAP).
Water samples from children’s households and community sources (public taps and wells) were analysed for contamination with faecal coliform bacteria and Escherichia coli by using the membrane filtration technique.
A hand-held global positioning system (GPS) device was used in the field to locate the interviewed households and the major environmental risk factors for diarrhoea (solid waste dumping, stagnant wastewater points, flood-prone areas and stagnant rainwater points in the city).
Results: The findings of this study showed that childhood diarrhoea had a varying spatial pattern across the city. The findings from the cross-sectional household surveys showed that 26% and 34% of the children surveyed in 2014 and in 2016 respectively were suffering from diarrhoea during the two weeks preceding the survey. The prevalence was higher among children living in the UCA in 2014 and in 2016 (36.3% and 38.3%) and in the PCA in 2014 and in 2016 (44.8% and 34.8%). In UCA, the highest prevalence was observed in the neighbourhood near coastal area, namely Tefess (57.1%), Zone Résidentielle (54.3%) and Golf (31.4%). In PCA, the highest prevalence was observed in the neighbourhood Baye Deuk (57.1%). Diarrhoeal prevalence were significantly associated with household sociodemographic characteristics, such as unemployment of mothers, use of open bags for storing household waste, evacuation of household waste in public streets, and use of shared toilets. Untreated stored drinking water and stored water contaminated with E. coli were associated with diarrhoea infections in children while drinking water source did not appear as a significant risk factor for diarrhoea.
Results from the time-series analysis showed a seasonal pattern of diarrhoeal cases in Mbour with two annual peaks: one peak in the cold dry season (December-March) and one peak in the rainy season (July-October). The study revealed that diarrhoeal cases were more clustered around urban settings compared to rural settings, and temperature and rainfall were associated with diarrhoeal incidence in Mbour.
Conclusion: Diarrhoeal diseases constitute an important public health problem among children under the age of 5 years in the secondary city of Mbour, Senegal. Our findings call for specific public health measures to tackle diarrhoea at the more affected areas, through the implementation of WASH intervention programmes, including promotion of solid waste and wastewater management, health education programmes for mothers of young children and family members about water treatment and storage, handwashing, the use of oral rehydration salt (ORS) and zinc supplementation and its preparation at household level, for a successful diarrhoea management.