Preventing trachoma through environmental sanitation: a review of the evidence base.

Methodological quality of the review: Low confidence

Author: Prüss A, Mariotti SP

Geographical coverage: Not reported

Sector: Trachoma

Sub-sector: Prevention, sanitation

Equity focus: None specified

Review type: Effectiveness review

Quantitative synthesis method: Narrative synthesis

Qualitative synthesis method: Not applicable

Background:

Trachoma remains the main cause of preventable blindness globally. The World Health Organisation (WHO) has therefore initiated a Global Alliance for the Elimination of Trachoma by 2020 (GET2020). The alliance has adopted the “SAFE” strategy, consisting of four components to give a combined medical, behavioural and environmental approach: Surgery of trachomatous trichiasis; Antibiotic treatment of active cases; promotion of Facial cleanliness; and initiation of Environmental changes to reduce the transmission of trachoma.

The association between personal and environmental sanitation has previously been noted. However, there is a need to investigate the role played by poor personal and environmental hygiene in the light of available studies, and to guide the F and E components of the SAFE strategy.

Objectives:

The review aimed to identify available evidence for the association between environmental sanitation and the transmission of trachoma, in order to then identify preventative interventions.

Main findings:

A total of 19 studies were included in the review. Studies were conducted from 39 different parts of the world. Four studies were clinical trials, and 15 were observational surveys. Parameters analysed in these studies included water availability, personal hygiene, garbage collection, absence of latrine/toilet, frequency of face-washing, facial cleanliness, fly density, presence of animals inside the house and indoor air quality.

Authors reported that the median protective effect on trachoma prevalence for improved access to water was 27% when considering distance to the water source. Six studies had positive results; one study had non-significant results. The influence of the quantity of available water was positive in two studies with a median protective effect of 21% and 76%, respectively, and non-significant in one study.

The presence of latrine was reported to be significant in all studies with a median reduction of trachoma prevalence of 28%. Garbage collection showed a median protection effect of 69% in two studies. Authors reported that the presence of animals inside the house was assessed by one study as being non-significant. Four studies which investigated the impact of flies of children or fly density on trachoma showed a protective effect for fewer flies, and one reported a non-significant result, with a median reduction in prevalence of trachoma.

Facial cleanliness was reported to be inversely associated with the prevalence of trachoma. Frequency of face washing was overall non-significant. Satisfactory personal hygiene was reported to have a positive impact by reducing trachoma prevalence by 48%.

Methodology:

Literature was searched for information on all transmission mechanisms for trachoma and the relative importance of transmission pathways.

Authors conducted a search on MEDLINE and Healthstar. The searches were not restricted to English language articles, and references cited in identified studies were checked for additional articles. Literature mentioned at the third meeting of the WHO Global Alliance for the Elimination of Trachoma was also included. In addition, three reviews undertaken in 2007 were checked for further studies.

Methods used to screen studies for inclusion and to extract data were not reported. In addition, authors did not report critically appraising included studies.

Applicability/external validity:

Authors noted that the validity of the studies could be affected by several factors: the main bias may arise because environmental risk factors – such as water availability, presence of latrine and garbage collection – tend to occur together in the same families and confound each other. Authors stated that this could lead to an overestimation of the studied association.

Geographic focus:

Authors did not discuss applicability of findings to low- and middle-income settings.

Summary of quality assessment:

Overall, there is low confidence in the conclusions about the effects of this study as important limitations were identified. Authors did not conduct a thorough search of the literature to ensure that all relevant studies were included in this review. Methods used to screen studies for inclusion and extract data of included studies were not reported. Therefore, it is not possible to conclude if important bias such as reporting bias were avoided within the review. In addition, authors did not report assessing the risk of bias of included studies.