Assessing secondary attack rates among household contacts at the beginning of the influenza A (H1N1) pandemic in Ontario, Canada, April-June 2009: A prospective, observational study

BMC Public Health

Research Article

Vidya Sunil¹  Anne-Marie Holt¹  Catherine Grift²  Eleanor Paget²  Rachel Savage³  Anne-Luise Winter³  Marie LaFreniere³  Ian Johnson⁴  Laura C Rosella⁴  Natasha S Crowcroft⁴  Michael Whelan⁵  Tina Badiani⁵  Deborah J Carr⁶  Crystal Frenette⁷  Maureen Horn⁷  Monali Varia⁷  Kathleen Dooling⁷  John Barbaro⁸  Michael King⁹  Elizabeth Rea^1,10  Freda Lam^1,11 

[1] Haliburton, Kawartha, Pine Ridge District Health Unit, Port Hope, Ontario, Canada;Middlesex-London Health Unit, London, Ontario, Canada;Ontario Agency for Health Protection and Promotion, Toronto, Ontario, Canada;Ontario Agency for Health Protection and Promotion, Toronto, Ontario, Canada;Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada;Ontario Ministry of Health and Long-Term Care, Toronto, Ontario, Canada;Oxford County Public Health and Emergency Services, Woodstock, Ontario, Canada;Peel Public Health, Mississauga, Ontario, Canada;Simcoe Muskoka District Health Unit, Barrie, Ontario, Canada;Sudbury & District Health Unit, Sudbury, Ontario, Canada;Toronto Public Health, Toronto, Ontario, Canada;York Region Health Department, Newmarket, Ontario, Canada;

关键词: Influenza;    Seasonal Influenza;    Health Unit;    Household Contact;    Primary Case;   

DOI  :  10.1186/1471-2458-11-234

 received in 2010-11-15, accepted in 2011-04-14,  发布年份 2011

来源: Springer

【 摘 要 】

BackgroundUnderstanding transmission dynamics of the pandemic influenza A (H1N1) virus in various exposure settings and determining whether transmissibility differed from seasonal influenza viruses was a priority for decision making on mitigation strategies at the beginning of the pandemic. The objective of this study was to estimate household secondary attack rates for pandemic influenza in a susceptible population where control measures had yet to be implemented.MethodsAll Ontario local health units were invited to participate; seven health units volunteered. For all laboratory-confirmed cases reported between April 24 and June 18, 2009, participating health units performed contact tracing to detect secondary cases among household contacts. In total, 87 cases and 266 household contacts were included in this study. Secondary cases were defined as any household member with new onset of acute respiratory illness (fever or two or more respiratory symptoms) or influenza-like illness (fever plus one additional respiratory symptom). Attack rates were estimated using both case definitions.ResultsSecondary attack rates were estimated at 10.3% (95% CI 6.8-14.7) for secondary cases with influenza-like illness and 20.2% (95% CI 15.4-25.6) for secondary cases with acute respiratory illness. For both case definitions, attack rates were significantly higher in children under 16 years than adults (25.4% and 42.4% compared to 7.6% and 17.2%). The median time between symptom onset in the primary case and the secondary case was estimated at 3.0 days.ConclusionsSecondary attack rates for pandemic influenza A (H1N1) were comparable to seasonal influenza estimates suggesting similarities in transmission. High secondary attack rates in children provide additional support for increased susceptibility to infection.

【 授权许可】

CC BY   
© Savage et al; licensee BioMed Central Ltd. 2011