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OBJECTIVES: Influenza household transmission studies are required to guide prevention strategies but most passively recruit index cases that seek healthcare. We investigated A(H1N1)pdm09 transmission in a household-based cohort during 2009. METHODS: Health-workers visited 270 households weekly, and collected swabs from influenza-like-illness cases. If A(H1N1)pdm09 was RT-PCR-confirmed, all household members had symptoms assessed and swabs collected daily for 10-15 days. Viral RNA was quantified and sequenced and serology performed on pre-pandemic sera. RESULTS: Index cases were detected in 20 households containing 81 people. 98.5% lacked A(H1N1)pdm09 neutralizing antibodies in pre-pandemic sera. Eleven (18.6%, 95% CI 10.7-30.4%) of 59 contacts were infected. Virus genetic diversity within households was negligible and less than between households. Index and secondary cases were distributed between mothers, daughters and sons, and had similar virus-RNA shedding and symptom dynamics. Fathers were rarely infected. Five secondary cases (45%) had no apparent symptoms and three shed virus before symptoms. Secondary infection was associated with index case wet cough (OR 1.56, 95% CI 1.22-1.99). CONCLUSIONS: In this cohort of A(H1N1)pdm09 susceptible persons, virus sequencing was capable of discriminating household from community transmission. Household transmission involved mothers and children but rarely fathers. Asymptomatic or pre-symptomatic shedding was common.

Original publication




Journal article


J Infect

Publication Date





581 - 590


Antibody, Household, Index, Influenza, Pandemic, Secondary, Serial interval, Shedding, Symptoms, Transmission, Adolescent, Adult, Aged, Aged, 80 and over, Antibodies, Viral, Asian Continental Ancestry Group, Child, Child, Preschool, Cohort Studies, Family Characteristics, Female, Genetic Variation, Humans, Infant, Infant, Newborn, Influenza A Virus, H1N1 Subtype, Influenza, Human, Male, Middle Aged, Prospective Studies, RNA, Viral, Sequence Analysis, DNA, Viral Load, Virus Shedding, Young Adult