title: Case-Based Surveillance of Pandemic (H1N1) 2009 in Maebashi City, Japan.
abstract: After national case-based surveillance for pandemic influenza A (H1N1) ceased on July 23,  2009, a daily case-based surveillance system was implemented in Maebashi City, Japan. All medical  facilities in the city reported all patients who had positive rapid antigen tests for influenza A.  When the epidemic exploded in late October, case-based surveillance for influenza-like illness  (ILI) was implemented from November 3, 2009 until the end of the epidemic. A total of 7,781  influenza cases were reported between July 25 and November 2, 2009, with a cumulative incidence  rate of 22.5 per 1,000 population. Nearly 70% of the patients were under 15 years old. Between  November 3, 2009 and the end of March 2010, a total of 16,394 ILI cases were reported, with a  cumulative incidence rate of 47.4 per 1,000 population. Of the ILI cases reported, 63% were in  patients younger than 15 years old. Only one death with laboratory confirmation of the H1N1  2009 virus was reported during the epidemic. The age-specific reproduction number among children  under 15 years of age was almost 1.40, whereas between children and adults (15 years of age and  above) it was considerably less than 1.0. The reproduction number derived from the next-generation  matrix using data from September 30 to October 14 was estimated to be 1.48 (95% confidence  interval, 1.41-1.56). Among individuals under 15 years of age, the infection rate calculated using  the final size equation under the assumption of no mitigation measures was nearly twice the rate  reported during the epidemic. These findings indicate that the majority of the transmission of  influenza A (H1N1) 2009 in the city occurred among children.
authors.affiliation: Maebashi Public Health Center, Gunma 371-0014, Japan. tsukui6568@city.takasaki.gunma.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tsukui
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D050936:Basic Reproduction Number; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000401:mortality / Q000635:transmission / Q000821:virology*; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D016019:Survival Analysis; D055815:Young Adult