Systematic review of the effects of climate factors on the prevalence and distribution of acute and chronic trachoma

摘要

Background: Trachoma is the world's leading cause of preventable blindness and is considered a neglected tropical disease. The primary causes of trachoma relate to poverty, but environmental factors (fly density, access to water and sanitation) are important and a key part of the SAFE intervention strategy. Trachoma prevalence is thought be associated with dry climates and exposure to dust. Aims: To investigate the evidence base for the direct impacts of current climate factors on trachoma prevalence and distribution. Methods: Systematic review of epidemiological studies that have quantified an association between meteorological observations or climate parameters and trachoma. The outcomes included were acute trachoma (to identify factors associated with transmission) and cicatricial/ blinding trachoma (to identify factors associated with scarring). Results: Eight papers met our strict criteria. Several papers reported an association between trachoma prevalence and altitude in African populations. Although most studies found that trachoma incidence declined at higher altitudes (providing some evidence of a role for temperature in transmission), some studies found the opposite effect. A robust mapping study found strong evidence of an association between low rainfall and active trachoma. There is also consistent but weak evidence that the prevalence of trachoma is higher in savannah-type ecological zones. No information was found on the effect of climate factors in low endemic areas or on the effect of dust on trachoma. Conclusions: Current evidence on the potential role of climate on trachoma is limited despite a wealth of anecdotal evidence. Temperature and rainfall factors appear to play a role in the transmission of active trachoma. However, the mechanisms are unclear and likely to be complex, particularly regarding the role of other environmental factors (such as flies), and behaviour in arid and semi-arid areas. Most studies did not adequately control for socioeconomic or environmental confounders.