Exploring the seasonal and regional features of cat-scratch disease on the basis of anti-Bartonella henselae IgM/IgG positive rates in Japan.

OBJECTIVES This study aimed to explore the seasonal and regional features of cat-scratch disease (CSD) based on 15-years of test results for anti-Bartonella henselae IgG and IgM by immunofluorescence assay (IFA) performed as a laboratory specialized in diagnostic testing of CSD in Japan. A literature search was performed to put our findings in perspective. METHODS A total of 956 sera from patients suspected of CSD were submitted to our laboratory from nationwide. Seasonal changes in the monthly positive rates of IgG/IgM antibodies and regional distribution of the test specimens were analyzed. RESULTS The monthly positive rates of anti-B. henselae IFA of IgG and IgM were both significantly high between September and January and low between March and July. The seasonal pattern observed in this study was similar to the ones reported from US and France, which were analyzed from a clinical database (monthly incidence of CSD diagnosis) or from monthly positive rates of either B. henselae PCR or anti-B. henselae IFA. However, fluctuations in the IFA monthly positive rates in this study were more pronounced than other reports. Regarding regionality, the test specimens submitted to us for IFA were prominently more from southwestern areas than from northern/middle-northern areas of Japan. The distribution coincided well with the regional distribution of CSD case reports and with a known regional prevalence of Bartonella-species bacteremia among pet cats in Japan. CONCLUSION These epidemiological features in Japan are of relevance in the clinical diagnoses of CSD.