AN OUTBREAK OF ASEPTIC MENINGITIS IN OKINAWA IN 1993

In the summer of 1993, an epidemic of aseptic meningitis had broken out in Okinawa island, the southernmost area of Japan. It started in June (or probably in May), reached a peak early in July and subsided in August. A total of 216 specimens (cerebrospinal fluids, throat swabs and sera) was collected from the patients with aseptic meningitis and viruses were recovered from 83 specimens (38.4%). Five isolates randomly selected were examined for the identification of the virus. The virus was identified as echovirus type 30 (echo-30) by plaque reduction neutralization test using enterovirus antiserum pools and monospecific antiserum. Large-plaque and small-plaque phenotypes of echo-30 were isolated. The two were neutralized by anti-echo-30 sera. For the plaque assay of echo-30 in RD-18S cells, the use of tragacanth gum for the overlay medium could reduce the incubation period to 25-30 hr.