Isolation of measles virus classified as D5 genotype during an outbreak in Kobe City, Japan, in 2007.

*Corresponding author: Mailing address: Kobe Institute of Health, 4-6 Minatojima-nakamachi, Chuo-ku, Kobe 650-0046, Japan. Tel: +81-78-302-6252, Fax: +81-78-302-0894, E-mail: kyoshi @mrg.biglobe.ne.jp Measles became widely prevalent in Japan in the spring of 2007 after an interval of 6 years (1). The reported number of measles cases started to increase in Kobe City at the beginning of May. The Health and Welfare Division of the Kobe City Government intensively implemented the measles surveillance. From May to December 2007, 155 patients aged 15 years or over and 100 patients aged under 15 years were reported to the Kobe Public Health Center as child and adult cases, respectively (Table 1). Peripheral blood and throat swab specimens were collected for virus isolation. Lymphocytes separated from peripheral blood specimens and throat swabs were inoculated with B95a cells (2). The development of multinucleated giant cells due to cell fusion, the characteristic cytopathic effect (CPE) of measles virus (MV), was checked everyday as a sign of virus isolation. Virus isolation was confirmed by indirect immunofluorescent test using antibody specific to MV. A total of 55 isolates were obtained from 41 patients; 40 isolates from lymphocyte specimens and 15 from throat swab specimens (Table 1). MV-isolation rates were higher with peripheral blood lymphocyte samples (56%) than with throat swab specimens (24%). The results suggest that peripheral blood samples are preferable as specimens for MV isolation. The time required for virus isolation in B95a cell culture was compared between vaccinated and non-vaccinated patients. The CPE characteristic of MV was observed at 0.9 ± 0.5 days after inoculation in specimens from nonvaccinated cases, with the earliest detection at 14 h after the inoculation, while CPE was observed at 3.1 ± 2.3 days in those from vaccinated patients. All 41 patients from whom MV was isolated demonstrated fever and rash as clinical symptoms except for one vaccinated patient who did not Jpn. J. Infect. Dis., 61, 2008