Effect of Water, Sanitation, and Hygiene on the Prevention of Trachoma: A Systematic Review and Meta-Analysis

BACKGROUND Trachoma is the world's leading cause of infectious blindness. The World Health Organization (WHO) has endorsed the SAFE strategy in order to eliminate blindness due to trachoma by 2020 through "surgery," "antibiotics," "facial cleanliness," and "environmental improvement." While the S and A components have been widely implemented, evidence and specific targets are lacking for the F and E components, of which water, sanitation, and hygiene (WASH) are critical elements. Data on the impact of WASH on trachoma are needed to support policy and program recommendations. Our objective was to systematically review the literature and conduct meta-analyses where possible to report the effects of WASH conditions on trachoma and identify research gaps. METHODS AND FINDINGS We systematically searched PubMed, Embase, ISI Web of Knowledge, MedCarib, Lilacs, REPIDISCA, DESASTRES, and African Index Medicus databases through October 27, 2013 with no restrictions on language or year of publication. Studies were eligible for inclusion if they reported a measure of the effect of WASH on trachoma, either active disease indicated by observed signs of trachomatous inflammation or Chlamydia trachomatis infection diagnosed using PCR. We identified 86 studies that reported a measure of the effect of WASH on trachoma. To evaluate study quality, we developed a set of criteria derived from the GRADE methodology. Publication bias was assessed using funnel plots. If three or more studies reported measures of effect for a comparable WASH exposure and trachoma outcome, we conducted a random-effects meta-analysis. We conducted 15 meta-analyses for specific exposure-outcome pairs. Access to sanitation was associated with lower trachoma as measured by the presence of trachomatous inflammation-follicular or trachomatous inflammation-intense (TF/TI) (odds ratio [OR] 0.85, 95% CI 0.75-0.95) and C. trachomatis infection (OR 0.67, 95% CI 0.55-0.78). Having a clean face was significantly associated with reduced odds of TF/TI (OR 0.42, 95% CI 0.32-0.52), as were facial cleanliness indicators lack of ocular discharge (OR 0.42, 95% CI 0.23-0.61) and lack of nasal discharge (OR 0.62, 95% CI 0.52-0.72). Facial cleanliness indicators were also associated with reduced odds of C. trachomatis infection: lack of ocular discharge (OR 0.40, 95% CI 0.31-0.49) and lack of nasal discharge (OR 0.56, 95% CI 0.37-0.76). Other hygiene factors found to be significantly associated with reduced TF/TI included face washing at least once daily (OR 0.76, 95% CI 0.57-0.96), face washing at least twice daily (OR 0.85, 95% CI 0.80-0.90), soap use (OR 0.76, 95% CI 0.59-0.93), towel use (OR 0.65, 95% CI 0.53-0.78), and daily bathing practices (OR 0.76, 95% CI 0.53-0.99). Living within 1 km of a water source was not found to be significantly associated with TF/TI or C. trachomatis infection, and the use of sanitation facilities was not found to be significantly associated with TF/TI. CONCLUSIONS We found strong evidence to support F and E components of the SAFE strategy. Though limitations included moderate to high heterogenity, low study quality, and the lack of standard definitions, these findings support the importance of WASH in trachoma elimination strategies and the need for the development of standardized approaches to measuring WASH in trachoma control programs.