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

Year: 2010

Type: article

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 defi ned as the household member with the earliest onset date of symptoms of acute respiratory infection (ARI), infl uenza-like illness (ILI), or laboratory-confi rmed 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 <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 >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 infl uenza.O n April 15 and 17, 2009, the fi rst 2 cases of pandem- ic (H1N1) 2009 in the United States were identifi ed among children in California; within 10 weeks, the strain was identifi ed in 99 countries or territories (1).Texas was the second US state to confi rm human transmission of pandemic (H1N1) 2009.On April 24, 2009, the Texas Department of State Health Services reported 2 patients with laboratory-confi rmed pandemic (H1N1) 2009 infection in Guadalupe County.The strain was similar to that isolated previously from patients in Mexico and California (2).On June 11, 2009, the World Health Organization raised the pandemic alert to phase 6, indicating that a global pandemic was under way (3).Characterizing transmission dynamics in various settings, such as households, schools, and the community, is critical to the development of appropriate guidance and public health interventions.Household contacts of persons with seasonal infl uenza are at increased risk for infection (4-7), but the household transmission characteristics of pandemic (H1N1) 2009 have yet to be fully characterized.This study reports household secondary attack rates and serial time intervals between illness onset in the index case-patient to illness onset in a household contact.We investigated persons with laboratory-confi rmed pandemic (H1N1) 2009 and their household contacts in 1 health service region of Texas. Methods PopulationThe Texas Department of State Health Services consists of 11 health service regions.We conducted our investigation in Health Service Region 8, which includes 28 counties in south-central Texas, bordered on the south by Mexico (Figure).Approximately 2.4 million persons live in the region; 1.5 million live in the city of San Antonio (8).

Source: Emerging infectious diseases

DOI: 10.3201/eid1604.091658