Household Transmission of Pandemic (H1N1) 2009, San Antonio, Texas, USA, April–May 2009

Oliver Morgan(Centers for Disease Control and Prevention), Sharyn E. Parks(Centers for Disease Control and Prevention), Trudi Shim(Centers for Disease Control and Prevention), Patricia Blevins(Centers for Disease Control and Prevention), Pauline Lucas(Centers for Disease Control and Prevention), Roger Sanchez(Centers for Disease Control and Prevention), Nancy Walea(Centers for Disease Control and Prevention), Fleetwood Loustalot(Centers for Disease Control and Prevention), Mark R. Duffy(Centers for Disease Control and Prevention), Matthew J. Shim(Centers for Disease Control and Prevention), Sandra Guerra(Centers for Disease Control and Prevention), Fernando Guerra(Centers for Disease Control and Prevention), Gwen Mills(Centers for Disease Control and Prevention), Jennifer R. Verani(Centers for Disease Control and Prevention), Bryan J. Alsip(Centers for Disease Control and Prevention), Stephen Lindstrom(Centers for Disease Control and Prevention), Bo Shu(Centers for Disease Control and Prevention), Shannon Emery(Centers for Disease Control and Prevention), Adam L. Cohen(Centers for Disease Control and Prevention), Manoj Menon(Centers for Disease Control and Prevention), Alicia M. Fry(Centers for Disease Control and Prevention), Fatimah S. Dawood(Centers for Disease Control and Prevention), Vincent P. Fonseca(Centers for Disease Control and Prevention), Sonja J. Olsen(Centers for Disease Control and Prevention)
Emerging infectious diseases
March 30, 2010
10.3201/eid1604.091658
Cited by 68Open Access
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Abstract

To assess household transmission of pandemic (H1N1) 2009 in San Antonio, Texas, USA, during April 15-May 8, 2009, we investigated 77 households. The index case-patient was defined as the household member with the earliest onset date of symptoms of acute respiratory infection (ARI), influenza-like illness (ILI), or laboratory-confirmed pandemic (H1N1) 2009. Median interval between illness onset in index and secondary case-patients was 4 days (range 1-9 days); the index case-patient was likely to be < or =18 years of age (p = 0.034). The secondary attack rate was 4% for pandemic (H1N1) 2009, 9% for ILI, and 13% for ARI. The secondary attack rate was highest for children <5 years of age (8%-19%) and lowest for adults > or =50 years of age (4%-12%). Early in the outbreak, household transmission primarily occurred from children to other household members and was lower than the transmission rate for seasonal influenza.

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