Dreyer, G., Rocha, A., Eunice Ribeiro, M., Norões, J., Addiss, D.
THE Og4C3 TEST FOR BANCROFTIAN FILARIASIS DIAGNOSIS: USE AND LIMITATIONS.
Anais da Faculdade de Medicina da Universidade Federal de Pernambuco. 41(1):43-47, 1996. (Portuguese)
The recently developed Og4C3 ELISA, which detects circulating Wuchereria bancrofti antigen, appears promising for use in epidemiologic surveys, but its sensitivity is unknown is persons with ultra-low microfilarial densities. We used the Og4C3 to test the sera of 282 patients who were microfilaria-positive in 1 to 16ml of blood, 18 patients who were microfilaria-negative but who had ultrasonographic or biopsy evidence of adult Wuchereria bancrofti infection, and 63 lifelong residents of a non-endemic area of Brazil . A total of 276 (97.9%) patients with detectable microfilaremia tested positive (optical density > 0.033). At microfilarial densities of < 1, 1-30 and > 30 microfilariae per ml of blood, the sensitivity of the Og4C3 was 72,2%, 97,6% and 100%, respectively (P<10 -6 ). The assay was positive in 66.7% of amicrofilaremic patients with evidence of adult worm infection and in one (1.6%) of 63 residents of non-endemic area (specificity, 98.4%). Thus, although generally high, the assay’s sensitivity decreased sharply in persons with microfilarial densities of < 1 microfilarial per ml. The authors also discuss that for appropriate epidemiologic and diagnostic use of Og4C3 assay, investigators and clinicians should be aware that positive predictive value decreases with low prevalence of infection, that a positive test result is not a marker of morbidity for bancroftian filariasis, and that a negative test result does not rules out the diagnosis of filarial infection or disease.