Emergence of Japanese encephalitis in a previously non-reported area: Three consecutive annual cases from a tertiary center in Narita, Chiba, Japan.

The number of Japanese encephalitis (JE) cases dramatically decreased after implementing national vaccination program in Japan and the diagnosis requires specific tests in the reference laboratory in most cases. We report three consecutive cases of JE in a single hospital in Narita over three years. Although the PCR test confirmed the diagnosis in one case, the PCR was negative and IgM captured ELISA in the reference laboratory confirmed the diagnosis in the other two cases. These cases suggest that the number of JE patients may be underestimated in Japan. Physicians should consider JE as a differential diagnosis, when encountering the cases of encephalitis or meningitis with unknown etiology during the warm season even in the area where JE has not been reported.