Factors associated with severe disease in hospitalized adults with pandemic (H1N1) 2009 in Spain

The risk factors for complications in patients with influenza A (H1N1)v virus infection have not been fully elucidated. We performed an observational analysis of a prospective cohort of hospitalized adults with confirmed pandemic influenza A (H1N1)v virus infection at 13 hospitals in Spain, between June 12 and November 10, 2009, to identify factors associated with severe disease. Severe disease was defined as the composite outcome of intensive‐care unit (ICU) admission or in‐hospital mortality. During the study period, 585 adult patients (median age 40 years) required hospitalization because of pandemic (H1N1) 2009. At least one comorbid condition was present in 318 (54.4%) patients. Pneumonia was diagnosed in 234 (43.2%) patients and bacterial co‐infection in 45 (7.6%). Severe disease occurred in 75 (12.8%) patients, of whom 71 required ICU admission and 13 (2.2%) died. Independent factors for severe disease were age <50 years (OR, 2.39; 95% CI, 1.05–5.47), chronic comorbid conditions (OR, 2.93; 95% CI, 1.41–6.09), morbid obesity (OR, 6.7; 95% CI, 2.25–20.19), concomitant and secondary bacterial co‐infection (OR, 2.78; 95% CI, 1.11–7) and early oseltamivir therapy (OR, 0.32; 95% CI 0.16–0.63). In conclusion, although adults hospitalized for pandemic (H1N1) 2009 suffer from significant morbidity, mortality is lower than that reported in the earliest studies. Younger age, chronic comorbid conditions, morbid obesity and bacterial co‐infection are independent risk factors for severe disease, whereas early oseltamivir therapy is a protective factor.