Community diagnosis of Bancroftian filariasis

Abstract

The objective of this study was to find the best tests for efficiently estimating the true prevalence of Bancroftian filariasis in endemic areas. The study population comprised 427 people over 10 years of age in an endemic village in Egypt. Four tests were evaluated; a standardized clinical examination, night blood examinations for microfilariae (50 μL thick films and 1 mL membrane filtration), and a test for circulating filarial antigen. 191 subjects (44·75%) had at least one positive test and were considered to have filariasis. The sensitivities of clinical examination, thick films, membrane filtration and antigen testing for filariasis were 16%, 50%, 64%, and 88%, respectively. Relative to membrane filtration of night blood, the filarial antigen test had a sensitivity of 97·5%, a positive predictive power of 71%, and a negative predictive power of 99%. None of the blood tests was a sensitive indicator of clinical filariasis; 69% of clinical cases were negative in all 3 blood tests and would have been missed if clinical examinations had not been done. Therefore, we recommend a combination of clinical examination and the filarial antigen test (with optional examination for microfilariae of those with positive antigen tests) for community diagnosis of Bancroftian filariasis in endemic areas.