Effect of water, sanitation and hygiene on the prevention of trachoma: a systematic review and meta-analysis
Methodological quality of the review: Medium confidence
Author: Stocks ME, Ogden S, Haddad D, Addiss DG, McGuire C, Freeman MC
Geographical coverage: Africa, Asia and Latin America
Sector: Trachoma
Sub-sector: Prevention, WASH
Equity focus: None specified
Review type: Effectiveness review
Quantitative synthesis method: Meta-analysis
Qualitative synthesis method: Not applicable
Background:
Trachoma is the world’s leading cause of infectious blindness. The World Health Organisation (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, both 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 programme recommendations.
Objectives:
To systematically review the literature and conduct meta-analyses (where possible) to report the effects of WASH on trachoma, and to identify research gaps.
Main findings:
In total, 86 studies were included in the review. 76 of the included publications were descriptive cross-sectional surveys, assessing at least one WASH-related condition or risk factor for chlamydia trachomatis infection or clinical disease. Ten publications involved some WASH-related intervention. 80% of the studies were conducted in Africa, 10% were conducted in Asia, and 10% were conducted in Latin America. In general, the quality of studies included in the meta-analyses was low.
Authors 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).
Facial cleanliness was significantly associated with reduced odds of TF/TI (OR 0.42, 95% CI 0.32–0.52), as were facial cleanliness indicators including 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 1km 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.
Overall, authors concluded that the findings of this review support the importance of WASH in trachoma elimination strategies and the need for the development of standardised approaches to measuring WASH in trachoma control programmes.
Methodology:
Authors conducted a search on PUBMED, EMBASE, ISI Web of Knowledge, MedCarib, Lilacs, REPIDISCA, DESASTRES and African Index Medicus databases with no restrictions on language or year of publication. In addition, authors examined seven previous reviews and hand-searched the bibliographies of all relevant publications.
Studies were included if they measured WASH exposure, trachoma infection and attempted to quantify the association between WASH exposure, condition or risk factor on trachoma. All study types were eligible for inclusion if they met the inclusion criteria. Two authors independently assessed the full text of studies for inclusion in the review, and data extraction was conducted independently on 10% of included studies. Authors assessed the quality of studies using the GRADE methodology.
For data analysis, authors conducted meta-analyses for all WASH-related exposures for which three or more studies reported comparable odds ratios (ORs) for the same WASH-trachoma association. WASH conditions included sanitation access, sanitation use, distance to water of less than 1km, a clean face, lack of ocular discharge, lack of nasal discharge, washing the face at least once daily, washing the face at least twice daily, bathing at least once daily, towel use and soap use.
Data was stratified by clinically-relevant trachoma measures. Funnel plots were used to analyse publication bias, and heterogeneity between studies was determined using Higgins’ I2 and Cochrane’s Q-tests. When heterogeneity was moderate to high, sub-group analyses were performed to identify potential sources of heterogeneity. Random-effects models were used throughout to enhance the generalizability of results.
Applicability/external validity:
Authors noted that the F and E components of the SAFE strategy, as well as hygiene, are well supported by evidence.
Geographic focus:
Included studies were conducted in Africa, Asia and Latin America, where there is a high prevalence of trachoma. Therefore, findings may only be applicable to these contexts.
Publication source:
Stocks ME, Ogden S, Haddad D, Addiss DG, McGuire C, Freeman MC. Effect of water, sanitation and hygiene on the prevention of trachoma: a systematic review and meta-analysis. PLoS Med. 2014 Feb 25;11(2):e1001605
Summary of quality assessment:
Overall, there is medium confidence in the conclusions about the effects of this study. Authors conducted a thorough search of the literature, and used appropriate methods to screen studies for inclusion, avoiding bias. However, data extraction was conducted by two reviewers independently only on 10% of the included studies. In addition, it is not clear from the review which studies were subject to high, medium or low risk of bias.
