Background: During the 2009 influenza A (H1N1) pandemic, household transmission studies were implemented to better understand the characteristics of the transmission of the novel virus in a confined setting.
Methods: We conducted a systematic review and meta-analysis to assess and summarize the findings of these studies. We identified 27 articles, around half of which reported studies conducted in May and June 2009.
Results: In 13 of the 27 studies (48%) that collected respiratory specimens from household contacts, point estimates of the risk of secondary infection ranged from 3% to 38%, with substantial heterogeneity. Meta-regression analyses revealed that a part of the heterogeneity reflected varying case ascertainment and study designs. The estimates of symptomatic secondary infection risk, based on 20 studies identifying febrile acute respiratory illness among household contacts, also showed substantial variability, with point estimates ranging from 4% to 37%.
Conclusions: Transmission of the 2009 pandemic virus in households appeared to vary among countries and settings, with differences in estimates of the secondary infection risk also partly due to differences in study designs.
From the aSchool of Public Health, The University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, China; bPRESTO, Japan Science and Technology Agency, Saitama, Japan; cVictorian Infectious Diseases Reference Laboratory, North Melbourne, Victoria, Australia.
Submitted 31 August 2011; accepted 6 February 2012; posted 3 May 2012.
This work received financial support from the Harvard Center for Communicable Disease Dynamics from the National Institute of General Medical Sciences (grant no. U54 GM088558), and the Area of Excellence Scheme of the University Grants Committee of Hong Kong (grant no. AoE/M-12/06). HN is supported by the JST PRESTO program. BJC has received research funding from MedImmune Inc. HAK has received funding from CSL Biotherapies. DKMI has received research funding from Roche. The authors reported no other financial interests related to this research.
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Correspondence: Hiroshi Nishiura, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Units 624-7, Cyberport 3, Pokfulam, Hong Kong. E-mail: firstname.lastname@example.org.