[Epidemiological study of the prevalence of influenza in Japan--regional differences in terms of three indices (development of epidemic outbreak, viral isolation, peak of prevalence)].

The prevalence of influenza in Japan was studied, dividing the whole country into six sections such as Tohoku, Hokkaido and Kanto, to determine regional differences from the nationwide viewpoint. This study was based on data obtained from a total of 720 prefectures where three of the first index (the time the epidemic outbreak developed), second index (the time the virus was isolated) and third index (the time the prevalence reached its peak) were determined for the 16 prevalence periods of influenza between 1976 and 1993. The mean value (standard deviation) of each index was obtained for each year of prevalence and for each area. The differences obtained were analyzed statistically, and the following results were obtained: 1. There was a marked regional difference in the development of epidemic outbreak of cold; it was earliest in the Kanto and Kinki areas (late November to early December) and latest in the Kyushu area (mid January). 2. Isolation of the virus was earliest in the Kanto and Kinki area (mid January) and latest in the Chugoku and Shikoku areas (late January to early February), showing a regional difference. 3. The peak of prevalence was earliest in the Kanto area (early February) and latest in the Tohoku, Hokkaido, Chugoku and Shinkoku areas (mid February), showing a regional difference. 4. The difference between the earliest and latest areas was 4.2 weeks regarding the first index, while it was decreased to 1.8 weeks for the second index and to 0.8 weeks for the third index.(ABSTRACT TRUNCATED AT 250 WORDS)