Abstract

Space-temporal trends of influenza like illness, Japan, in 1999-2009
Track: Health and Human Services
Authors: Yugo Shobugawa, Seth Wiafe, Reiko Saito, Hiroshi Suzuki

From 1999 to 2009, we analyzed >11.1 million cases of influenza like illness (ILI) in Japan based on national surveillance data. It was shown that standard distance, which measures spatial compactness of a distribution, weighted by magnitude of weekly ILI cases per sentinel in prefectural level was a possible indicator for prediction of timing of initiation of yearly influenza outbreak. Typical trend of weighted standard distance (WSD) was shown as a pattern such that it reached the smallest value before starting epidemic nationwide, and then, increased through epidemic. This rule was applicable for nine of the ten study seasons. Further, it was suggested that timing of bottom WSD was related with types/subtypes of circulating influenza viruses. We concluded continuous observation and spatial statistical analyses on the national influenza surveillance are useful to understand transmission patterns of influenza, and further beneficial to take adequate measures beforehand from the public health perspective.