Background: It is necessary to analyse the severe cases of pandemic influenza infection in order to identify vulnerable populations and adapt prevention and control policies accordingly. We analysed the clinical and epidemiological characteristics and risk factors associated with death in patients with 2009 pandemic influenza A (H1N1) infection hospitalised in intensive care units (ICUs) in Spain and reported from 24 April 2009 to 31 January 2010.
Methods: As part of the national strategy for surveillance of hospitalized cases with pandemic influenza, cased-based clinical and epidemiological information on all cases admitted to an ICU with 2009 pandemic virus (H1N1) infection was collected nationwide.
Results: Of 1,231 cases admitted to ICU, 271 died (case fatality ratio, 22%). The median age was 40 years (range: 0-90). A total of 838 (76.3%) patients had an underlying risk condition, being respiratory disease the most frequently reported (34.1%), followed by morbid obesity (18.8%), in adults. Antiviral treatment was given in 93.1% patients and in 25.6% (n = 231) it was initiated within 48 hours of symptoms onset. In a multivariate analysis, cancer (OR 2.71, 95%CI 1.44 to 5.1), immunodeficiency (OR 2.25, 95%CI 1.29 - 3.92) and morbid obesity (OR 1.79, 95%CI 1.13 to 2.85) were significantly associated with death in adults.
Conclusions: The characterization of severe pandemic influenza cases has been crucial in identifying as risk factors of complications and death from influenza the presence of cancer and immunodeficiencies and for the first time, morbid obesity in adults.