The use of Bartonella henselae-specific age dependent IgG and IgM in diagnostic models to discriminate diseased from non-diseased in Cat Scratch Disease serology.

Cat Scratch Disease (CSD) is caused by Bartonella henselae infection and is a common cause of regional lymphadenopathy. The diagnosis of CSD largely depends on serology, but is hampered by both low sensitivity and specificity of the applied IgG and IgM assays. Using an in-house ELISA, we detected a significant age-dependent increase in the IgG levels in the general population compared to CSD patients. With this knowledge, we developed diagnostic models to differentiate diseased from non-diseased persons. Evaluation of these models using samples from PCR-positive patients (n=155) and age-matched controls (n=244) showed an important increase in the assay performance if the combination of the IgG and IgM results were taken into account. If the specificity was set at 98% the sensitivity was only 45% and 32% for the IgM and IgG ELISA, respectively but increased to 59% when these results were combined. Also the use of age-dependent factors further improved the clinical relevance of the outcome raising the sensitivity to 64%. Although the sensitivity of the ELISA remains low we conclude that the use of models using the combination of both IgM and IgG test results and age-depending factors can be a useful diagnostic tool in the serodiagnosis of CSD.