Correlates of severe disease in patients with 2009 pandemic influenza (H1N1) virus infection

• Published in: Canadian Medical Association journal 2010-02, Vol.182 (3), p.257-264
• Main Authors: Zarychanski, Ryan, Stuart, Tammy L, Kumar, Anand, Doucette, Steve, Elliott, Lawrence, Kettner, Joel, Plummer, Frank
• Format: Article
• Language: English
• Subjects: Adult; Analysis; Antiviral agents; Antiviral Agents - therapeutic use; Antiviral drugs; Canada - epidemiology; Care and treatment; Case-Control Studies; Chronic Disease - ethnology; Comorbidity; Disease Outbreaks; Female; Guidelines as Topic; Hospitalization; Humans; Immunization; Indians, North American - statistics & numerical data; Influenza; Influenza A Virus, H1N1 Subtype - isolation & purification; Influenza viruses; Influenza, Human - ethnology; Influenza, Human - rehabilitation; Influenza, Human - virology; Intensive Care Units - statistics & numerical data; Male; Manitoba - ethnology; Medical research; Medicine, Experimental; Pandemics; Prospective Studies; Severity of Illness Index; Swine flu
• ISSN: 0008-4409; 0820-3946; 1488-2329
• DOI: 10.1503/cmaj.091884

In the context of 2009 pandemic influenza (H1N1) virus infection (pandemic H1N1 influenza), identifying correlates of the severity of disease is critical to guiding the implementation of antiviral strategies, prioritization of vaccination efforts and planning of health infrastructure. The objective of this study was to identify factors correlated with severity of disease in confirmed cases of pandemic H1N1 influenza. This cumulative case-control study included all laboratory-confirmed cases of pandemic H1N1 influenza among residents of the province of Manitoba, Canada, for whom the final location of treatment was known. Severe cases were defined by admission to a provincial intensive care unit (ICU). Factors associated with severe disease necessitating admission to the ICU were determined by comparing ICU cases with two control groups: patients who were admitted to hospital but not to an ICU and those who remained in the community. As of Sept. 5, 2009, there had been 795 confirmed cases of pandemic H1N1 influenza in Manitoba for which the final treatment location could be determined. The mean age of individuals with laboratory-confirmed infection was 25.3 (standard deviation 18.8) years. More than half of the patients (417 or 52%) were female, and 215 (37%) of 588 confirmed infections for which ethnicity was known occurred in First Nations residents. The proportion of First Nations residents increased with increasing severity of disease (116 [28%] of 410 community cases, 74 [54%] of 136 admitted to hospital and 25 [60%] of 42 admitted to an ICU; p