A case of leptospirosis contracted through occupational exposure in the Tokyo metropolitan area

Leptospirosis is a zoonotic disease caused by direct or indirect contact with rodent reservoirs. Although it is widely known to be endemic in tropical countries, several cases have been reported even in metropolitan areas of non-tropical countries. Herein, we report a case of leptospirosis caused by occupational exposure in the Tokyo metropolitan area. A 24-year-old man presented with fever, headache, and systemic arthralgia. Laboratory tests revealed thrombocytopenia, abnormal liver function, and impaired renal function. Although he denied any direct contact with rats, his workplace was contaminated with them, which was key to the diagnosis. Leptospira interrogans serogroup Icterohaemorrhagiae ST17 was identified as the causative agent based on multilocus sequence typing of the urine sample and the microscopic agglutination test of the paired serum samples. Subsequent epidemiological investigation revealed that L. interrogans serogroup Icterohaemorrhagiae ST17 was isolated from rats captured in the vicinity of the patient's workplace. To the best of our knowledge, this is the first case of leptospirosis in Japan in which the same Leptospira genotype was identified in both the patients and the rats trapped around the patient's workplace. Although there is a widespread misconception that leptospirosis is a tropical disease, several cases are reported annually even in non-tropical industrialized cities, such as Tokyo, where rodents play a significant role in human infection. Diagnosis of leptospirosis is sometimes challenging for clinicians, but the first step in diagnosis is to recognize that there is always a risk of infection with Leptospira spp. in any environment potentially contaminated by rats.