LAUSR

identified as the preceding infection in 42–69% of ReA patients (3). According to population-based studies, the annual incidence of ReA is reported to be 0.6–27/ 100,000 (4). On the other hand, there is a report showing that 4.1% of patients with C. trachomatis infection developed ReA (5). However, thus far, there have been no reports showing the prevalence of Chlamydia-associated ReA in a prospective study. Therefore, the prevalence of Chlamydia-associated ReA has not been confirmed yet. To assess the prevalence of Chlamydia-associated ReA among patients attending an urban clinic of general practice and rheumatology in Tokyo, a prospective study was conducted. Chlamydia trachomatis genital infection was proved using standard PCR testing with urine samples from these patients. Using a standardized questionnaire, 123 consecutive Japanese adults, with proven C. trachomatis genital infection, were screened for symptoms of ReA. A follow-up questionnaire was administered at least 6 weeks later by telephone or through a revisit to the clinic. Patients who claimed at least one symptom of arthritis were evaluated by a rheumatologist for the diagnosis of ReA. These 123 male patients (median age 34.5 years, range 19–76 years) were enrolled in this study from 2009 to 2016 (Table 1). Twelve out of 123 patients were also positive forNeisseria gonorrhoeae, as determined by PCR. Only one patient out of the 123 patients has developed ReA. This patient was 31 years old and developed arthritis of the sacroiliac joints. Therefore, it is concluded that the prevalence of Chlamydia-associated ReA among patients with C. trachomatis genital infections is lower than reported previously. One of the reasons for this discrepancy may be the early effective treatment with antibiotics in this study. In this study, all the patients with C. trachomatis genital infection were treated with 1 g of azithromycin in a single dose and evaluated for the abolition of infection 1–2 weeks after treatment using nucleic acid amplification testing (PCR). In contrast to the results presented in a recent report (6), in this observational study, no treatment failure was observed in Japanese male patients with a single use of azithromycin. Taken together, it is speculated that a certain period of persistent infection with C. trachomatis is required for the development of Chlamydia-associated ReA. Further prospective studies with a larger cohort are required to elucidate the role of C. trachomatis infection in the development of ReA through the interaction of this pathogen and immune system.