Contagious period for pandemic (H1N1) 2009

DOI: 10.3201/eid1605.091894
Suggested citation for this article: De Serres G, Rouleau I, Hamelin M-E, Quach C, Skowronski D, Flamand L, et al. Contagious period for pandemic (H1N1) 2009. Emerg Infect Dis. 2010 May; [Epub ahead of print]

Contagious Period for Pandemic (H1N1) 2009

Gaston De Serres, Isabelle Rouleau, Marie-Eve Hamelin, Caroline Quach, Danuta Skowronski, Louis Flamand, Nicole Boulianne, Yan Li, Julie Carbonneau, Anne-Marie Bourgault, Michel Couillard, Hugues Charest, and Guy Boivin
Author affiliations: Institut National de Santé Publique du Québec, Quebec City, Quebec, Canada (G De Serres, I. Rouleau, N. Boulianne, A.M. Bourgault, M. Couillard, H. Charest), Laval University, Quebec City (G. De Serres, M.-E. Hamelin, L. Flamand, J. Carbonneau, G. Boivin); McGill University–Montreal Children's Hospital, Montreal, Quebec, Canada (C. Quach); British Columbia Centers for Disease Control, Vancouver, British Columbia, Canada (D. Skowronski); and Public Health Agency of Canada, Winnipeg, Manitoba, Canada (Y. Li)

We estimated the proportion of persons with pandemic (H1N1) 2009 who were shedding infectious virus at diagnosis and on day 8 of illness. In households with confirmed cases, nasopharyngeal swabs were collected on all members and tested by PCR and virus culture. Of 47 cases confirmed by PCR at <7 days of illness, virus culture was positive in 92% (11/12) of febrile and 63% (22/35) of afebrile persons. Of 43 persons with PCR-confirmed pandemic (H1N1) 2009 from whom a second specimen was collected on day 8, 74% remained PCR positive and 19% were culture positive. If the 73 symptomatic household members without PCR-confirmed illness are assumed to have pandemic (H1N1) 2009, a minimum of 8% (6/73) of case-patients shed replicating virus on day 8. Self-isolation only until fever abates appears insufficient to limit transmission. Self-isolation for a week may be more effective, although some case-patients still would shed infectious virus.

Since April 2009, an influenza A virus, pandemic (H1N1) 2009, has spread to most countries of the world. Widespread susceptibility of persons <60 years of age may have facilitated rapid dissemination (1). Transmissibility of influenza viruses depends on duration of shedding, amount of virus shed, and other factors that may facilitate projection of virus into the environment, such as coughing or sneezing. Challenge studies in healthy volunteers inoculated
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