Pandemic influenza hospitalization in Spain (2009): incidence, in-hospital mortality, comorbidities and costs.

Based on data drawn from the national hospitalization discharge registry, we sought to describe the clinical and epidemiological characteristics of patients hospitalized with pandemic influenza H1N1 in Spain in 2009. Authors calculated national rates of hospitalization stratified by age and analyzed co-morbidities, in hospital mortality, average length of stay and associated medical costs. A total of 11,449 patients were hospitalized (24.9/100,000 inhabitants). Median age was 34 y and 50.28% were male. The highest incidence was observed in the group from 0 to 14 y (42.3/100000 inhabitants), 27.7% of hospitalized women of childbearing age were pregnant and overall in hospital mortality reached 2.46%. The average length of stay was 5 d, median costs per admission was €2,152 and total cost was €35.4 million. Among those patients, 5,791 (50.6%) had an underlying chronic disease: asthma (15.36%), diabetes (9.02%), obesity (8.47%), cancer (4.47%), epilepsy (2.24%), and HIV (2.22%). Suffering a chronic condition was an independent risk factor for dying (OR 13.31 95% for 0-14 y and OR 3.27 for 15-64 y). We conclude that hospitalization was higher in infants and in young adults with associated co-morbidities. Suffering a chronic condition increased the risk of dying as the age decreased. This information will be helpful to prepare vaccination strategies against next pandemic threats.