Screening
The World Health Organization (WHO) recommends the initiation of public health interventions if the prevalence of active disease in children aged 1 to 9 years is more than 10%.[36] It recommends the initiation of a surgical programme if the prevalence of trichiasis in people aged over 15 years is more than 1%.[22]
Screening is a key component of the attempt to eliminate trachoma. Communities where trachoma is known or suspected to be endemic must be screened. The diagnosis of trachoma in an individual should lead to a community-wide assessment of the prevalence of trachoma. Individual treatment alone is futile; because of the facile transmission of trachoma, an individual may be rapidly re-infected and not all patients with ocular chlamydial infection will present with signs of disease and those with signs of disease may not have infection. Therefore, a community-wide intervention is the best approach to treat endemic trachoma within a community.
Community survey method (recommended by WHO)
A community survey should be conducted in an area known or suspected to have endemic trachoma, or in response to the discovery of trachoma in an individual within a community suspected of having endemic trachoma. Communities that historically had trachoma and are thought to have eliminated it should also be monitored.
Community prevalence is the key diagnostic determinant for initiating a trachoma control programme. Community-wide screening can be undertaken. However, this may be unnecessary in large communities where a sample of people will provide the necessary information.
The WHO recommends that trachoma screening be undertaken at the administrative health district level; this approximates to a region containing about 100,000 people. The burden of disease should be estimated by sampling the district. The process for determining the sample to be examined is complex and has been outlined by the WHO.[30] Estimates on the cost of trachoma monitoring are available.[37]
Other survey methods
A variety of survey methods have been trialled, each with their own strengths and weaknesses.[30][38][39] A technique based on Lot Quality Assurance Sampling continues to examine children until either a predetermined cut-off has been reached or 50 children have been examined: the rationale being that if the cut-off point is reached, an intervention is called for, and to continue sampling is an inefficient use of resources. If the cut-off is not reached, then no intervention is required.[30]
Alternatively, Trachoma Rapid Assessment (TRA) is a technique that attempts to identify those most likely to have trachoma by sampling those who live in the poorest conditions or have the greatest risk factors for trachoma. This does not necessarily provide an estimate of prevalence, but it helps to prioritise communities within a district for intervention. Furthermore, TRA may be a powerful tool to quickly confirm whether trachoma has been eliminated from a region.[38]
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