Epidemiological and molecular studies of measles at different clusters in hokkaido district, Japan, 2007.

In 2007 eight epidemic clusters (more than 15 cases in each) and other sporadic cases of measles occurred in Hokkaido district, Japan. A total of 850 cases were identified. Approximately half of them were > or = 15 years of age, resulting in a huge public health problem in the community associated with school closings, and 31% of the cases reported that they already had a history of vaccination. Of 28 isolates of the measles virus detected, all were identified as genotype D5, identical to the type isolated in other areas of Japan, suggesting that a highly homologous measles virus circulated in Japan. The occurrence pattern of measles patients and molecular epidemiology indicated that the measles virus that spread in Hokkaido district might not be indigenous.