Background: Influenza pandemics may cause more severe cases. The objective was to determine the characteristics of hospitalized severe cases of pandemic influenza in Catalonia and to study risk factors for admission to intensive care unit (ICU).
Methods: A prospective epidemiologic study of new cases of pandemic influenza hospitalized by their severity between June 2009 and May 2010. Hospitals were asked to declare laboratory confirmed pandemic influenza cases that met the case specific case definition for severe case. A standardized epidemiological survey was conducted to collect information on demographics, clinical characteristics, risk factors, treatment and outcome. Differences between the cases in ICU compared to other severe cases were studied with the odds ratio (OR), which were adjusted using a logistic regression model.
Results: We detected total of 773 pandemic influenza (H1N1) 2009 severe cases; 465 (60.2%) of them had at least one risk factor and the most prevalent were: pregnancy 19 (13%), asthma 87 (12%), chronic obstructive pulmonary disease 87 (11.4%) and heart disease 80 (10.5%). Required admission to ICU 293 patients (37.9%). Factors associated with ICU admission were obesity BMI>40 (adjusted OR = 2.5, 95% CI 1.4-4.5) and chronic liver disease (adjusted OR = 2.3, 95% CI 1.1-4.8).
Conclusions: This study confirms the high prevalence of pregnancy, chronic respiratory diseases, diabetes and obesity among pandemic influenza severe cases. Obesity acts as a risk factor for ICU admission and should therefore be considered as an indicator for influenza vaccination.