To the Editor: I was impressed by the recent publication by Aita et al. who reported a surprisingly high seroprevalence rate for Rickettsia typhi within resident populations on Honshu Island, Japan (1). The authors pointed out the possibility of murine typhus reemergence in Japan, where the disease has been reported only sporadically (2). However, the conclusions might be premature because the study was cross-sectional, and only 1 timepoint was evaluated. Many cases of murine typhus could have occurred in the distant past, which might not be reflected in this type of study. A previous study in Spain showed a high incidence rate in patients who were much younger (mean age of ≈46 years) (3) than those reported in this study (mean age of 67 years). A study in Greece showed frequent epidemiologic links to flea exposure (4), but the study in Japan did not investigate this apparent risk factor. I do not believe that age-related differences in flea exposures exist in Japan; hence, it is likely that exposures might have occurred in the past, when persons in Japan had a lower standard of hygiene. According to another study, the median half-life of R. typhi IgG was 177 days, and the median IgG titer was 800 at day 365 postinfection, suggesting long-lasting seropositivity (5). Therefore, the relatively stringent cutoff value of R. typhi serology in this study (1) could have overestimated the prevalence. To demonstrate that murine typhus is indeed a reemerging disease in Japan, further actual cases in Japan need to be identified, or similar seroprevalence studies should be repeated in other regions to determine trends in R. typhi seropositivity.

Top

Related Links

• More Letter Articles