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Clin Infect Dis. 2010 Oct 1. [Epub ahead of print]
Household Transmission of the 2009 Pandemic A/H1N1 Influenza Virus: Elevated Laboratory‐Confirmed Secondary Attack Rates and Evidence of Asymptomatic Infections.
Papenburg J, Baz M, Hamelin MX, Rh X00e9 Aume C, Carbonneau J, Ouakki M, Rouleau I, Hardy I, Skowronski D, Roger M, Charest H, De X00a0 Serres G, Boivin G.
Infectious Disease Research Center of the Centre Hospitalier Universitaire de Québec‐CHUL and Laval University and 2Institut National de Santé Publique du Québec, Quebec City, and 3Centre de Recherche du Centre Hospitalier Universitaire de Montréal et Département de Microbiologie et Immunologie de l’Université de Montréal, Montreal, Quebec, and 4British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada.
Abstract
Background.  Characterizing household transmission of the 2009 pandemic A/H1N1 influenza virus (pH1N1) is critical for the design of effective public health measures to mitigate spread. Our objectives were to estimate the secondary attack rates (SARs), the proportion of asymptomatic infections, and risk factors for pH1N1 transmission within households on the basis of active clinical follow‐up and laboratory‐confirmed outcomes. Methods.  We conducted a prospective observational study during the period May–July 2009 (ie, during the first wave of the pH1N1 pandemic) in Quebec City, Canada. We assessed pH1N1 transmission in 42 households (including 43 primary case patients and 119 contacts). Clinical data were prospectively collected during serial household visits. Secondary case patients were identified by clinical criteria and laboratory diagnostic tests, including serological and molecular methods. Results.  We identified 53 laboratory‐confirmed secondary case patients with pH1N1 virus infection, for an SAR of 45% (95% confidence interval [CI], 35.6%–53.5%). Thirty‐four (81%) of the households had ⩾1 confirmed secondary case patient. The mean serial interval between onset of primary and confirmed secondary cases was 3.9 days (median interval, 3 days). Influenza‐like illness (fever and cough or sore throat) developed in 29% (95% CI, 20.5%–36.7%) of household contacts. Five (9.4%) of secondary case patients were asymptomatic. Young children (<7 years of age) were at highest risk of developing laboratory‐confirmed influenza‐like illness. Primary case patients with both diarrhea and vomiting were the most likely to transmit pH1N1. Conclusion.  Household transmission of pH1N1 may be substantially greater than previously estimated, especially in association with clinical presentations that include gastrointestinal complaints. Approximately 10% of pH1N1 infections acquired in the household may be asymptomatic.
PMID: 20887206 [PubMed - as supplied by publisher]
Household Transmission of the 2009 Pandemic A/H1N1 Influenza Virus: Elevated Laboratory‐Confirmed Secondary Attack Rates and Evidence of Asymptomatic Infections.
Papenburg J, Baz M, Hamelin MX, Rh X00e9 Aume C, Carbonneau J, Ouakki M, Rouleau I, Hardy I, Skowronski D, Roger M, Charest H, De X00a0 Serres G, Boivin G.
Infectious Disease Research Center of the Centre Hospitalier Universitaire de Québec‐CHUL and Laval University and 2Institut National de Santé Publique du Québec, Quebec City, and 3Centre de Recherche du Centre Hospitalier Universitaire de Montréal et Département de Microbiologie et Immunologie de l’Université de Montréal, Montreal, Quebec, and 4British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada.
Abstract
Background.  Characterizing household transmission of the 2009 pandemic A/H1N1 influenza virus (pH1N1) is critical for the design of effective public health measures to mitigate spread. Our objectives were to estimate the secondary attack rates (SARs), the proportion of asymptomatic infections, and risk factors for pH1N1 transmission within households on the basis of active clinical follow‐up and laboratory‐confirmed outcomes. Methods.  We conducted a prospective observational study during the period May–July 2009 (ie, during the first wave of the pH1N1 pandemic) in Quebec City, Canada. We assessed pH1N1 transmission in 42 households (including 43 primary case patients and 119 contacts). Clinical data were prospectively collected during serial household visits. Secondary case patients were identified by clinical criteria and laboratory diagnostic tests, including serological and molecular methods. Results.  We identified 53 laboratory‐confirmed secondary case patients with pH1N1 virus infection, for an SAR of 45% (95% confidence interval [CI], 35.6%–53.5%). Thirty‐four (81%) of the households had ⩾1 confirmed secondary case patient. The mean serial interval between onset of primary and confirmed secondary cases was 3.9 days (median interval, 3 days). Influenza‐like illness (fever and cough or sore throat) developed in 29% (95% CI, 20.5%–36.7%) of household contacts. Five (9.4%) of secondary case patients were asymptomatic. Young children (<7 years of age) were at highest risk of developing laboratory‐confirmed influenza‐like illness. Primary case patients with both diarrhea and vomiting were the most likely to transmit pH1N1. Conclusion.  Household transmission of pH1N1 may be substantially greater than previously estimated, especially in association with clinical presentations that include gastrointestinal complaints. Approximately 10% of pH1N1 infections acquired in the household may be asymptomatic.
PMID: 20887206 [PubMed - as supplied by publisher]
