Pandemic influenza A (H1N1) virus in households with young children

BACKGROUND Influenza viruses may cause a severe infection in infants and young children. The transmission patterns of pandemic 2009 influenza A (H1N1) within households with young children are poorly characterized. METHODS Household members of six children younger than 1·5 years with documented 2009 influenza A (H1N1) infection were studied by daily symptom diaries and serial parent-collected nasal swab samples for detection of influenza A by reverse transcription polymerase chain reaction (RT-PCR) assay. RESULTS Laboratory-confirmed, symptomatic influenza was documented in 11 of 15 household contacts of young children with pandemic influenza (73%; 95% CI, 48-99). In five contact cases symptoms started earlier, in three cases on the same day, and in three cases after the onset of symptoms in the youngest child. The first case with influenza A (H1N1) within the household was an elder sibling in two households, father in two households, the youngest child in one household, and the youngest child at the same time with a sibling in one household. The median copy number of influenza virus was higher in children than in adults (4·2 × 10(7) versus 4·9 × 10(4), P = 0·02). CONCLUSIONS This study demonstrates the feasibility of nasal swab sampling by parents in investigation of household transmission of influenza. The results support influenza vaccination of all household contacts of young children.