Secondary attack rates (SARs) of the 2009 pandemic H1N1 influenza A in households.

*At risk population - the number of individuals included in attack rate calculation.&contacts who did not use prophylaxis.#Virological confirmation was performed as follows:For index cases: RT PCR for 76.7% of individuals and serology for 23.3% of individuals.For contacts: Serology- 100% of individuals.‡115 contacts of 41 index cases.&clinical diagnosis in the context of school outbreak with virologically confirmed 2009 H1N1 influenza A cases.∧Diagnosed primarily with a rapid influenza A test with 242 of them confirmed by a pandemic (H1N1) PCR. The study was carried out during a time that the pandemic (H1N1) influenza A was the predominant influenza A virus circulating in Japan. This study includes data from the Ghani study [6]. The index case was not the first sick case in most families.