Evaluation of a latex agglutination test for Rickettsia conorii antibodies in seropositive patients.

A latex agglutination test for antibodies to Rickettsia conorii was compared with micro-immunofluorescence (the reference test for total antibodies); 179 sera were from 115 confirmed cases of Mediterranean Spotted Fever, and 101 were from pregnant women (control group) who had no detectable antibodies by the reference method. The micro-immunofluorescence test for specific IgM antibodies was used to clarify some discordant results. The agreement obtained between latex-R. conorii and micro-immunofluorescence was 95%. Sensitivity and specificity were 96% and 93% respectively. When micro-immunofluorescence results for specific IgM antibodies were included, these figures rose to 96 and 99%, and agreement was almost 97%. Latex agglutination is a simpler and more rapid technique than micro-immunofluorescence and is suitable for the screening as well as for the titration of R. conorii antibodies.