Risk factors for hospitalization and severe outcomes of 2009 pandemic H1N1 influenza in Quebec, Canada

Abstract

Please cite this paper as: Gilca et al. (2011) Risk Factors for Hospitalization and Severe Outcomes of 2009 Pandemic H1N1 Influenza in Quebec, Canada. Influenza and Other Respiratory Viruses 5(4), 247–255 Background/ Objective This case–control study was carried out to estimate risk factors associated with hospitalizations and severe outcomes [intensive care unit (ICU) admission or death] among patients with illness because of laboratory‐confirmed 2009 pandemic A/H1N1 virus (pH1N1) during the first wave of pH1N1 activity in the province of Quebec, Canada. Patients/ Methods We collected epidemiologic information by phone using a standardized questionnaire from patients with laboratory‐confirmed pH1N1 illness during the first spring/summer pandemic wave in Quebec, Canada. Risk factors associated with hospitalization were assessed by comparing hospitalized to community cases and for ICU admission or death through comparison with hospitalized cases. Results Cases (321 hospitalized patients including 47 ICU admissions and 15 deaths) were compared to controls (395 non‐hospitalized patients) by using multivariable logistic regression adjusted for gender, age, education, being a health care worker, smoking, seasonal influenza vaccination, delay to consultation, antiviral use before admission, pregnancy, underlying medical conditions, and obesity. Age <5 years, underlying medical conditions (neuromuscular, cardiac, pulmonary, and renal conditions, diabetes, asthma, and other), and delayed consultation were associated with hospitalization. The strongest association with hospitalization was observed for neuromuscular disorders. Antiviral medication before hospital admission protected against severe disease. Association of obesity with hospitalization was not significant after adjustment in multivariable analysis. Among hospitalized patients, age ≥60 years and immune suppression were associated with death. Conclusions Previously identified risk factors for seasonal influenza were also associated with increased risk of severe pH1N1 outcomes. The independent role of obesity needs to be further defined.

Description of Hospitalized Cases of Influenza A(H1N1)pdm09 Infection on the Basis of the National Hospitalized-Case Surveillance, 2009&ndash;2010, Japan

“…CFR in those aged 20 years and older was significantly higher than that in those aged under 20 years. These results were consistent with the results from previous reports and reaffirmed that A(H1N1)pdm09 virus infection led to high morbidity in the young population and a high CFR in the elderly population (4,(7)(8)(9)(10)(11).…”

“…This rate is similar to those found in Mexico, Chile, and Brazil and 50z of the rate observed in Australia, the Unites States, and Argentina during the same period (6,7). Consistent with the results described in other reports, over 80z of hospitalized cases in the present study were young (＜20 years) (4,(7)(8)(9)(10)(11)35). It is interesting to note that the results from several studies have indicated that the elderly were not disproportionately affected by the virus, perhaps because of cross immunity to A(H1N1)pdm09 in this population (12)(13)(14).…”

Neuraminidase inhibitors for influenza: a systematic review and meta-analysis of regulatory and mortality data

“…[113][114][115][116][117][118] The included trials were predominantly conducted in adults during influenza seasons in both hemispheres. A small number of studies were conducted in older people who were residing in care homes and in people with underlying respiratory diseases.…”

Eosinophils Promote Antiviral Immunity in Mice Infected with Influenza A Virus

“…Patients with chronic lung disease (including asthma), heart disease, diabetes, and obesity were among the most commonly hospitalized during the 2009 influenza pandemic (2-4), emphasizing the importance of understanding influenza pathogenesis in patients with underlying chronic conditions. Paradoxically, retrospective studies investigating the 2009 influenza pandemic demonstrated that although asthmatics were more likely to be hospitalized, they were less likely to have complications or die of influenza compared with non-asthmatics (5)(6)(7)(8)(9). Although the use of corticosteroids has been proposed as one reason for this confounding observation (10), information on steroid therapy was not available in all reports surrounding the 2009 influenza pandemic, nor have steroids been found to be effective against influenza infections (11,12).…”