ELISA and indirect immunofluorescent assays evaluation for IgM antibodies detection against Rickettsiosis

Abstract

We evaluated two modified tests of ELISA and indirect immunofluorescence (IFI) for detecting IgM based on the total lysate of Rickettsia Akari for Rickettsiosis diagnosing. 55 negative sera were used, 100 positive sera confirmed by IFI IgGTotal and 15 sera with a confirmed diagnosis for other bacterial diseases from the serum of the Instituto Nacional de Salud (Lima, Perú). IgM ELISA test had a sensitivity of 78.0%, 80.0% specificity, positive predictive value of 87.6% and negative predictive value of 66.7%, and have a 20% (3/15) cross-reaction with other bacterial aetiologies. The IFI IgM test had a sensitivity of 82.0%, specificity of 91.7%, positive predictive value of 94.3% and negative predictive value of 75.3%, with a 13% (2/15) cross-reaction. The IgM ELISA test is not useful, unlike the IFI IgM test that could be applied in diagnosing Rickettsiosis for surveillance and epidemiological studies in Peru.