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

Oliver Morgan ,Sonja J Olsen,Matthew J Shim,Fernando Guerra,Sandra Guerra,Adam L Cohen,Bo Shu,Alicia M Fry,Fleetwood Loustalot,Gwen Mills,Trudi Shim,Vincent P Fonseca,Manoj Menon,Nancy Walea,Roger Sanchez,Mark R Duffy,Stephen Lindstrom,Bryan Alsip,Shannon Emery,Sharyn E Parks ,Pauline Lucas ,Fatimah S Dawood ,Patricia Blevins ,Jennifer R Verani

doi:10.3201/eid1604.091658

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.

Highlights

The pandemic appears to have moderate severity in comparatively well-off countries, it is prudent to anticipate a bleaker picture as the virus spreads to areas with limited resources, poor health care, and a high prevalence of underlying medical problems
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Summary

Introduction

The pandemic appears to have moderate severity in comparatively well-off countries, it is prudent to anticipate a bleaker picture as the virus spreads to areas with limited resources, poor health care, and a high prevalence of underlying medical problems.

Results

Conclusion