Severe leptospirosis in a patient with positive serological test for spotted fever rickettsiosis.

Here, we report a case of a 64-year-old man with severe leptospirosis infected in an area in Japan that is non-endemic to leptospirosis. Initially, findings of high-grade fever, mild generalised arthralgia, rashes on the trunk, mild thrombocytopenia, elevated liver enzymes and renal dysfunction led to the suspicion of rickettsiosis, which was an endemic infectious disease in the area. Subsequently, leptospirosis was also considered after carefully reviewing patient history, which revealed that he may have been exposed to mice urine. Finally, leptospirosis was diagnosed after the serum indicated a positive PCR for leptospirosis. Furthermore, due to serum antibody positivity for Rickettsia japonica, false-positivity or coinfection of spotted fever rickettsiosis was suspected. Despite the delayed diagnosis, the patient recovered with antibiotic treatment. Thus, to prevent diagnostic errors, leptospirosis should be potentially considered with high suspicion in patients with acute undifferentiated fever, even in non-endemic areas of leptospirosis.