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Volume 16, Number 4—April 2010

Research

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

Oliver W. MorganComments to Author , Sharyn Parks, Trudi Shim, Patricia A. Blevins, Pauline M. Lucas, Roger Sanchez, Nancy Walea, Fleetwood Loustalot, Mark R. Duffy, Matthew J. Shim, Sandra Guerra, Fernando Guerra, Gwen Mills, Jennifer Verani, Bryan Alsip, Stephen Lindstrom, Bo Shu, Shannon Emery, Adam L. Cohen, Manoj Menon, Alicia M. Fry, Fatimah Dawood, Vincent P. Fonseca, and Sonja J. Olsen
Author affiliations: Centers for Disease Control and Prevention, Atlanta, Georgia, USA (O.W. Morgan, S. Parks, F. Loustalot, J. Verani, S. Lindstrom, B. Shu, S. Emery, A.L. Cohen, M. Menon, A.M. Fry, F. Dawood, S.J. Olsen); Department of State Health Services, Austin, Texas, USA (S. Parks, T. Shim, N. Walea, S. Guerra, V.P. Fonseca); United States Air Force School of Aerospace Medicine, Brooks City-Base, Texas, USA (P.M. Lucas, M.R. Duffy, M.J. Shim); San Antonio Metropolitan Health District, San Antonio, Texas, USA (P.A. Blevins, R. Sanchez, F. Guerra, B. Alsip); Comal County Health Department, New Braunfels, Texas, USA (G. Mills)

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Table 2

Household secondary attack rates for ARI, ILI, and laboratory-confirmed pandemic (H1N1) 2009, by age group, Region 8, Texas, April–May 2009*

Illness type by age group, y No. index 
case-patients Household contacts
Household members not included Secondary attack rate (A/A + B), %
Secondary 
case-patients, A Not ill, B Total household contacts, A + B
ARI
<5 7 5 23 28 1 18
5–18 50 13 83 96 3 14
19–49 17 11 96 107 3 10
>50 3 3 22 25 1 12
All ages
77
32
224
256
8
13
ILI
<5 6 5 23 28 2 18
5–18 50 11 86 97 2 11
19–49 18 6 102 108 1 6
>50 3 2 23 25 1 8
All ages
77
24
234
258
6
9
Laboratory-confirmed pandemic (H1N1) 2009
<5 8 2 26 28 0 7
5–18 51 5 92 97 1 5
19–49 16 3 108 111 0 3
>50 2 1 26 27 0 4
All ages 77 11 252 263 1 4

*ARI, acute respiratory infection; ILI, influenza-like illness (fever measured or subjective and cough or sore throat). Ill household members were not included in the calculation of the secondary attack rate if they had the same symptom onset as the index case or if symptom onset was not known.

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