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Laboratory-confirmed pandemic H1N1 influenca in hospitalized adults – findings from the Canadian Nosocomial Infection Surveillance Program (CNISP), 2009-10

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Introduction / objectives

To describe laboratory-confirmed pandemic H1N1 (pH1N1) influenza in adult inpatients at participating Canadian hospitals between June 2009 and May 2010 and compare to previous years’ seasonal surveillance.


Adult inpatients (>=16 years) with lab confirmed influenza were enrolled. Variables collected included ICU admissions and death attributed to influenza assessed 30 days after initial diagnosis.



Thirty-seven hospitals submitted data on 701 cases. The median age of was 49 years (range 16 - 94). Vaccine history was available for 314 cases, and 21% (n=65) reported receiving vaccine. Oseltamivir was given to 90% of the cases a median of 3 days after symptom onset (range 0 - 24). Influenza-associated admission to ICU was required for 28% (n=197). The 30 day all-cause mortality was 7%; influenza was the primary cause of 20 deaths and contributed to death in a further 22 cases for an influenza-attributed mortality of 6%. The mean age at death was 50 years (SD 13.8).


The ICU admission rate and influenza-attributed mortality were similar to three preceding influenza years, but mean age at death was significantly younger (p<0.01). Antivirals were prescribed for more patients with influenza (90%) than in previous seasons (35-47%). The pH1N1 virus appeared outside the traditional influenza season and impacted a different age group than seasonal viruses circulating in previous years, highlighting the importance of ongoing influenza surveillance.

Disclosure of interest

None declared.

Author information

Correspondence to G Taylor.

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This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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About this article


  • Influenza
  • Initial Diagnosis
  • Symptom Onset
  • Oseltamivir
  • Influenza Season