Clinical manifestations of Lyme borreliosis (LB), caused by Borrelia burgdorferi sensu lato (Bbsl), include erythema migrans, Lyme neuroborreliosis (LNB), carditis, and arthritis. LB is a notifiable disease in Japan with <30 surveillance-reported LB cases annually, predominately from Hokkaido Prefecture. However, LB, including LNB, may be under-diagnosed in Japan since diagnostic tests are not readily available. We sought to determine if LNB could be a cause of previously undiagnosed encephalitis or meningitis in Japan. Investigators at 15 hospitals in 10 prefectures throughout Japan retrieved serum and/or cerebrospinal fluid (CSF) samples collected in 2010-2021 from 517 patients hospitalized with encephalitis or meningitis which had an etiology that had not been determined. Samples were tested for Bbsl-specific antibodies using ELISA and Western blot tests. In alignment with the European Union LNB case definition, a confirmed LNB case had CSF pleocytosis and intrathecal production of Bbsl-specific antibodies and a probable LNB case had a CSF sample with pleocytosis and Bbsl-specific antibodies. LNB was identified in three hospitalized patients with meningitis of previously undetermined etiology: a male resident of Aomori Prefecture was a confirmed LNB case, and two female residents of Oita Prefecture were probable LNB cases. None of the patients with confirmed or probable LNB had traveled in the month prior to symptom onset and none had samples previously tested for LB. The identification of previously undiagnosed LNB cases indicates a need for enhanced disease awareness in Japan, particularly beyond Hokkaido Island, and more readily available LB diagnostic testing.

Lyme neuroborreliosis in Japan: <i>Borrelia burgdorferi</i> sensu lato as a cause of meningitis of previously undetermined etiology in hospitalized patients outside of the island of Hokkaido, 2010–2021

Lyme neuroborreliosis in Japan: Borrelia burgdorferi sensu lato as a cause of meningitis of previously undetermined etiology in hospitalized patients outside of the island of Hokkaido, 2010–2021