Effect of sanitation on soil-transmitted helminth infection: systematic review and meta-analysis

Kathrin Ziegelbauer, Benjamin Speich, Daniel Mäusezahl, Robert Bos, Jennifer Keiser, Jürg Utzinger, Kathrin Ziegelbauer, Benjamin Speich, Daniel Mäusezahl, Robert Bos, Jennifer Keiser, Jürg Utzinger

Abstract

Background: In countries of high endemicity of the soil-transmitted helminth parasites Ascaris lumbricoides, Trichuris trichiura, and hookworm, preventive chemotherapy (i.e., repeated administration of anthelmintic drugs to at-risk populations) is the main strategy to control morbidity. However, rapid reinfection of humans occurs after successful deworming, and therefore effective preventive measures are required to achieve public health goals with optimal efficiency and sustainability.

Methods and findings: We conducted a systematic review and meta-analysis to assess the effect of sanitation (i.e., access and use of facilities for the safe disposal of human urine and feces) on infection with soil-transmitted helminths. PubMed, Embase, ISI Web of Science, and the World Health Organization Library Database were searched without language restrictions and year of publication (search performed until December 31, 2010). Bibliographies of identified articles were hand-searched. All types of studies reporting data on sanitation availability (i.e., having access at own household or living in close proximity to sanitation facility), or usage, and soil-transmitted helminth infections at the individual level were considered. Reported odds ratios (ORs) of the protective effect of sanitation on soil-transmitted helminth infections were extracted from the papers or calculated from reported numbers. The quality of published studies was assessed with a panel of criteria developed by the authors. Random effects meta-analyses were used to account for observed heterogeneity. Thirty-six publications, consisting of 39 datasets, met our inclusion criteria. Availability of sanitation facilities was associated with significant protection against infection with soil-transmitted helminths (OR = 0.46 to 0.58). Regarding the use of sanitation, ORs of 0.54 (95% confidence interval [CI] 0.28-1.02), 0.63 (95% CI 0.37-1.05), and 0.78 (95% CI 0.60-1.00) were determined for T. trichiura, hookworm, and A. lumbricoides, respectively. The overall ORs, combining sanitation availability and use, were 0.51 (95% CI 0.44-0.61) for the three soil-transmitted helminths combined, 0.54 (95% CI 0.43-0.69) for A. lumbricoides, 0.58 (95% CI 0.45-0.75) for T. trichiura, and 0.60 (95% CI 0.48-0.75) for hookworm.

Conclusions: Despite a number of limitations (e.g., most studies used a cross-sectional design and were of low quality, with potential biases and considerable heterogeneity), our results reveal that sanitation is associated with a reduced risk of transmission of helminthiases to humans. Access to improved sanitation should be prioritized alongside preventive chemotherapy and health education to achieve a durable reduction of the burden of helminthiases.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1. Flowchart visualizing the procedure for…
Figure 1. Flowchart visualizing the procedure for identifying relevant publications.
Overall, 36 publications were identified, containing 39 datasets (A). Number of hits (B) and ultimate identification of relevant publications (C) are also shown, for three different electronic databases. STH, soil-transmitted helminths. aMultiple exclusion criteria possible.
Figure 2. Meta-analysis examining the association of…
Figure 2. Meta-analysis examining the association of sanitation facilities with A. lumbricoides infection.
Data are presented separately for availability and use of sanitation. Rectangles indicate ORs, and sizes of the rectangles represent the weight given to each study in the meta-analysis; open diamonds and vertical dashed lines indicate combined ORs; and horizontal lines indicate 95% CIs. Data are presented separately for aonly pit latrine, bonly solar urine-diverting desiccating latrine, conly adults, donly children. N.A., not assessed.
Figure 3. Meta-analysis examining the association of…
Figure 3. Meta-analysis examining the association of sanitation facilities with T. trichiura infection.
Data are presented separately for availability and use of sanitation. Rectangles indicate ORs, and sizes of the rectangles represent the weight given to each study in the meta-analysis; open diamonds and vertical dashed lines indicate combined ORs; and horizontal lines indicate 95% CIs. Data are presented separately for aonly pit latrine, bonly solar urine-diverting desiccating latrine, conly adults, donly children. N.A., not assessed.
Figure 4. Meta-analysis examining the association of…
Figure 4. Meta-analysis examining the association of sanitation facilities with hookworm infection.
Data are presented separately for availability and use of sanitation. Rectangles indicate ORs, and sizes of the rectangles represent the weight given to each study in the meta-analysis; open diamonds and vertical dashed lines indicate combined ORs; and horizontal lines indicate 95% CIs. Data are presented separately for aonly pit latrine, bonly solar urine-diverting desiccating latrine, conly adults, donly children. N.A., not assessed.
Figure 5. Meta-analysis examining the association of…
Figure 5. Meta-analysis examining the association of sanitation facilities with infection with the three common soil-transmitted helminths combined.
Data are presented separately for availability and use of sanitation. Rectangles indicate ORs, and sizes of the rectangles represent the weight given to each study in the meta-analysis; open diamonds and vertical dashed lines indicate combined ORs; and horizontal lines indicate 95% CIs. Data are presented separately for aonly adults and bonly children.

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