Screening of Microfilariasis in Blood (Loa Loa) among the Immigrant Population in Endemic Areas

BACKGROUND: Given the increasing flux of immigrant population from high-risk areas to our country, the need of screening for loasis arises, despite systematic screening being a debated and poorly evaluated practice to which there is no protocol. This study is aimed at identifying the population to which loasis screening would be most appropriate, by drawing a comparison among four alternatives. METHODS: Case and control group study, involving 30 cases (all those who came to our unit for treatment and who tested positive for Loa Loa in a microfilariae in the blood detection test) and 90 control cases (three controls per case from among the subjects having tested negative for microfiliariae in the blood chosen at random without any pairing criteria). RESULTS: Of the 1,638 subjects on whom the microfilariae blood test was performed, 30 tested positive (1.8%; 1.2-2.6%). Of these 30 cases of loasis, 76.7% (23; 57.7-90.1%) had eosinophilia (OR 8.8; 3.3-23.1; p<0.0001) and 30.0% (9; 14.7-49.4%) compatible clinical symptoms (OR 2.8; 1.0-7.5; p=0.04). If we were to apply the screening test to the entire immigrant population coming from endemic areas, we would have to perform 54.6 tests to detect one case. If we were to perform the test on patients showing eosinophilia and/or compatible clinical symptoms, we would have to perform a smaller number of tests for every case detected (NNS=29; IC=21-48), but there would be 16.7% (5; 5.7-34.7%) false negatives. CONCLUSIONS: Conducting a screening test with determination of microfiliariae in the blood on the immigrant population coming from Central and West Africa, independently of the presence of eosinophilia or compatible clinical symptoms, would be indicated, provided that the necessary resources are available.