Pandemic Influenza Virus Surveillance, Izu-Oshima Island, Japan

Tomoko Inamasu¹, Kouji Sudo, Shingo Kato, Hiroshi Deguchi, Manabu Ichikawa, Tadanori Shimizu, Tadami Maeda, Shuhei Fujimoto, Toru Takebayashi, and Tomoya Saito²

Author affiliations: Author affiliations: Keio University Global Security Research Institute, Tokyo, Japan (T. Inamasu, K. Sudo, S. Kato, H. Deguchi, T. Saito); Keio University School of Medicine, Tokyo (K. Sudo, S. Kato, T. Takebayashi, T. Saito); Tokyo Institute of Technology, Kanagawa, Japan (H. Deguchi, M. Ichikawa); Oshima Medical Center, Tokyo (T. Shimizu); Maeda Internal Medicine Clinic, Tokyo (T. Maeda); Tokai University School of Medicine, Kanagawa (S. Fujimoto)

Abstract

A population-based influenza surveillance study (using PCR virus subtyping) on Izu-Oshima Island, Japan, found that the cumulative incidence of influenza A(H1N1)pdm09 virus infections 2 seasons after the pandemic was highest for those 10–14 years of age (43.1%). No postpandemic A(H1N1)pdm09 case-patients had been infected with A(H1N1)pdm09 virus during the pandemic season.

The dynamics of an influenza epidemic are difficult to determine because they vary for each circulating influenza subtype. We evaluated the epidemiology of influenza A subtypes at Oshima Medical Center and Maeda Internal Medicine Clinic on Izu-Oshima Island, Japan. The island is a semiclosed community, which facilitates population-based surveillance. Access to the island is limited; ≈18,000 persons travel to and from the island each month, primarily to and from Tokyo (1). Izu-Oshima Island is 120 km southwest of Tokyo; population was 8,856 in January 2009.