Clinical utility of indirect fluorescent assay for IgA class antibodies against Bartonella henselae in serodiagnosis of cat scratch disease in its early stage.

The utility of IgA class antibodies for the serodiagnosis of cat scratch disease (CSD) was evaluated by developing an indirect immunofluorescent assay (IFA) using an antigen obtained by co-cultivating Bartonella henselae ATCC 49882 with Vero cells. Served for evaluation were 101 sera from patients serologically confirmed as CSD with IgG-IFA ≥1:256, and 144 sera from patients clinically suspected of CSD but not serologically confirmed. The sensitivity of the newly developed IgA-IFA in detecting the confirmed cases was 57.4% (58/101), and 75.0% in combination with IgM-IFA. As for the non-confirmed cases, IgA-IFA turned 8.3% cases (12/144) positive, 10 of whom were subsequently diagnosed as CSD of early stage from clinical courses and/or by repeated testing. The 12-case gain was regarded as a significant improvement. Hence, the diagnostic rate of early-stage CSD is expected to be increased by routinely performing IgA-IFA in addition to conventional IgG/IgM-IFA.