Diagnostic target product profiles for monitoring, evaluation and surveillance of schistosomiasis control programmes
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DTAG recommendations for schistosomiasis diagnostic Target Product Profiles
The WHO Diagnostic Technical Advisory Group (DTAG) was formed under the advice of the WHO Strategic and Technical Advisory Group for NTDs, to ensures a unified approach to identifying and prioritizing diagnostic needs, and to informing WHO strategies and guidance on the subject.
DTAG recommended that the diagnostic Target Product Profiles (TPPs) for Schistosoma mansoni and S. haematobium were:
- monitoring and evaluation of schistosomiasis control programmes; and
- determining if transmission has been interrupted and when to conduct post-MDA surveillance.
TPP for monitoring and evaluation
Health ministries currently lack effective tools for monitoring and evaluation of schistosomiasis control programmes. Egg detection can be used, but the cost, challenges of obtaining samples, and the need for trained personnel and equipment limit the frequency of monitoring. The purpose of this TPP is to guide the development of new diagnostic tools to reliably measure when prevalence is above or below a cut-off of 10% in school-aged children (Table 1). Communities remaining above 10% require annual MDA, while communities below 10% can reduce MDA frequency as long as < 10% prevalence can be maintained. However, the lack of a reliable test has hindered the development of maintenance strategies. The test is also needed to track changes of prevalence > 10% to ensure that annual MDA is reducing overall prevalence. Use of the test in a survey should be less expensive that 2–3 rounds of MDA, the number of treatments
expected to demonstrate a meaningful difference in prevalence. Field workers should be able to perform and interpret the test with only a single day of training, and any equipment used for reading the test should be highly portable and battery powered if it needs electricity at all. The amount of time for collecting samples, performing the test, interpreting the data and making a treatment decision should be less than one working day so that only a single field visit would be required for each community.
TPP for transmission interruption and surveillance
Programmes currently lack effective tools for conducting surveillance and for determining when schistosomiasis transmission has been interrupted. Traditional egg detection methods have the high specificity necessary for successful elimination programmes but lack sensitivity, especially in infections of low intensity that are most likely encountered in interruption of transmission scenarios. The purpose of this TPP is to guide the development of new diagnostic tools to reliably detect 3% infection prevalence (Table 2). While this cut-off may seem relatively high, realistically, it can be achieved by using an economical lot quality assurance sampling approach (LQAS) by which any confirmed positive would trigger additional intervention measures. Even using the 3% cut-off, a combined, two-step test approach will be necessary to achieve the required survey testing specificity. By this approach, an initial (lower cost) screening test with higher sensitivity would be coupled with a secondary test with higher specificity that might be more expensive, but would be utilized with a more limited sample size (and would have the option of being centralized). To attain the required survey specificity, a positive result in both tests would be needed to confirm an active infection. In a limited prevalence or “post-elimination” surveillance situation, tests otherwise unable to distinguish active from former infections (e.g. current antibody tests) could be used in children younger than the number of years transmission is thought to have been interrupted, as all such individuals should be negative. Antibody responses that linger after treatment could also be used for initial screening purposes in older individuals if followed by a test confirming if there is an active infection. Antibodies to antigens that clear after treatment could be used for all age groups