Relationships between shared sanitation facilities and diarrhoeal and soil-transmitted helminth infections: an analytical review

Shared sanitation is widely proposed as a means to increase access to improved sanitation. There are few reports of a causal relationship between the use of shared sanitation and communityacquired diarrhoea. This paper presents an analytical review of studies that have investigated the relationship between the use of shared sanitation and the prevalence of (1) diarrhoeal disease and (2) soil-transmitted helminth (STH) infections. Data were extracted from the reviewed literature to calculate odds ratios (ORs) and confidence intervals (CIs). The use of shared sanitation showed a significant increase in diarrhoeal diseases, with an overall OR of 2.39 (85% CI 1.15–8.31). Children under 5 years were slightly less affected with a prevalence ratio of 1.09 (95% CI 1.06–1.12). The number of published reports on STH infections in relation to shared sanitation was limited, but the few that do exist report on ‘improved sanitation’, showing a positive and protective impact with an overall OR of 0.49 (95% CI 0.28–0.89), which is contrary to the negative impact related to diarrhoea. Despite the limited information on the direct link between shared sanitation and incidence of diarrhoeal/STH infections, this literature review demonstrates that the relationship deserves close attention in future practice and research. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). doi: 10.2166/washdev.2019.180 om http://iwa.silverchair.com/washdev/article-pdf/9/2/198/643608/washdev0090198.pdf er 2020 P. S. Ramlal (corresponding author) Sershen School of Life Sciences, University of KwaZulu-Natal, Durban, KwaZulu-Natal, 4001, South Africa E-mail: preshod.ramlal@durban.gov.za T. A. Stenström I. D. Amoah Institute for Water and Wastewater Technology, Durban University of Technology, Durban, KwaZulu-Natal, South Africa S. Munien School of Agriculture, Earth and Environmental Sciences, University of KwaZulu-Natal, Durban, KwaZulu-Natal, 4001, South Africa C. A. Buckley Pollution Research Group, University of KwaZulu-Natal, Durban, KwaZulu-Natal, 4001, South Africa This article has been made Open Access thanks to the generous support of a global network of libraries as part of the Knowledge Unlatched Select initiative.


INTRODUCTION
Poor or unimproved sanitation is associated with high disease burdens worldwide, which includes diarrhoea and soil-transmitted helminths (Clasen et al. ). Diarrhoea accounts for the largest burden of disease from poor sanitation, with an estimated 1.4 million deaths per year (Prüss-Üstün et al. ; Sclar et al. ). Diarrhoeal disease, in general, is a major cause of morbidity and mortality, particularly in low-and middle-income countries (Black et al. ). In addition to being ranked as the  (Fewtrell et al. ). Sanitation excludes disease-causing microorganisms from the environment, thereby acting as a primary barrier to infection (Freeman et al. ). Additionally, unhygienic practices could contribute to over 23% of diarrhoeal cases (WHO ). Practices including a lack of handwashing in relation to defaecation, food and water handling have been implicated (Curtis & Cairncross ). Approximately 54% of diarrhoeal cases can be reduced with an improvement in handwashing behaviour, especially for severe diarrhoea (48%) and Shigellosis (59%) (Fewtrell et al. ).
Access to clean and adequate water supply supports hygiene and sanitation and could, therefore, be beneficial in preventing diarrhoea and other infections (Bartram & Cairncross ). Additionally, safe water at the points of collection, treatment and storage all play important roles in preventing diarrhoea (Benova et al. ). Accessibility to water is also a major contributory factor in diarrhoeal infections (Esrey et al. ). The WHO estimates that over 1.1 billion people globally rely on unsafe drinking water (WHO ).
Over 88% of the global cases of diarrhoea are attributed to unsafe water, sanitation and hygiene (WHO ), which further relates to behaviour that may either lead to an increase or decrease in infection (Dreibelbis et al. ).
This influences the adoption of water, sanitation and hygiene practices or technologies aimed at diarrhoea reduction (Dreibelbis et al. ).
Infection with STHs is often linked to poverty, poor hygiene and lack of clean water (Brooker ; Utzinger et al. ). Approximately 4.5 billion people are at risk of soil-transmitted helminth (STH) infection worldwide, with over 1.5 billion people infected presently (WHO ).
Poor sanitation may contribute to the elevated risk of STH infections by increasing the number of infective eggs in the environment, including in soil, thereby promoting the risks of egg ingestion (King & Bertino ; Brooker ).
Additionally, the infection may occur due to penetration of the skin by hookworm larvae (Bethony et al. ). Improvements in sanitation can be achieved through both the upgrading of sanitation facilities and the promotion of According to the JMP, shared sanitation is either considered 'limited', where improved sanitation is shared between two or more households, or 'unimproved', when this shared facility is a pit latrine without a slab or platform (WHO & UNICEF ). Based on this classification, as at 2015, 76% of the global population use improved sanitation.
Since approximately 68% of the 76% population with improved sanitation did not share, they were counted as basic sanitation services. Sewer connections were available for 36% of the non-shared improved sanitation, with the rest using septic tanks, latrines and other improved on-site sanitation facilities, therefore falling under the 'safely mana-   (Table 1). In Africa, for example, close to 44% of the population is reported to rely on some form of shared sanitation, which is the highest proportion of the population using this type of sanitation worldwide.
A number of countries in Africa, such as Ghana, Liberia and Sierra Leone, also have figures far above the regional average (Table 1). South-East Asia follows with the next highest proportion of use of shared sanitation (31.3%).
Improved sanitation has been shown to reduce diar- Although the situation is partly case-specific, it is important for local authorities, public and environmental health practitioners and other key policy-makers to consider the relationship between shared sanitation and the incidence of different diseases, especially diarrhoea within rapidly developing cities. This information will be useful in the design and implementation of appropriate interventions, especially within informal settlements or slums. The current contribution reviews the global literature on shared sanitation with the objective of investigating the potential linkages between the use of shared sanitation facilities and the incidence of diarrhoea and STH infections.

Data extraction
This review is based on literature searches using the following databases for all publications up to 3 October 2018: Pub Med; Web of Science, ScienceDirect and Google Scholar.
The publications emerging from the searches were screened manually for relevant information. Articles that met the criteria were analysed to extract data/information on the causal relationship between the use of shared sanitation facilities and the incidence of diarrhoea and STH infections.
Information such as case studies used, types of shared sanitation studied and measured outcomes were also collated. Additionally, information on the type of sanitation was recorded for the control populations, where stated.
The limitations associated with the respective studies were noted.

Assessment of bias and quality of evidence
The quality of methods was judged by assessing the representativeness of the study sample and the nature of the population from which the sample was drawn (Zaccai

Shared sanitation and soil-transmitted helminth infections
The relationship between STH infections and the use of shared sanitation is under-investigated. The findings from the few reported investigations are summarised in Figure 2 showing an overall protective effect of shared sanitation.