Contagious Period for Pandemic (H1N1) 2009 | CDC EID

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Volume 16, Number 5–May 2010
Research
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)

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Abstract
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 with seasonal influenza viruses have shown that shedding generally coincides with symptom onset starting 1 day after inoculation, peaks on the second day, and generally ends 1 week after disease onset, on day 8 (2). Duration of shedding is greatly affected by age, and for seasonal influenza viruses is longer in young children than in adults (3–5). Since the emergence of pandemic (H1N1) 2009, the recommended duration of self-isolation has varied from complete resolution of symptoms to 1 day after fever has subsided (6,7). The objective of this study was to estimate the proportion of pandemic (H1N1) 2009–infected persons shedding infectious virus 1 week after illness onset.

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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 [serial on the Internet]. 2010 May [date cited]. http://www.cdc.gov/EID/content/16/5/783.htm

DOI: 10.3201/eid1605.091894