[Influenza: a four-year evolution of the pandemic. Prof. Alejandro Posadas National Hospital, Argentina].
As from January to August 2013, epidemiological weeks 1-35 (EW), Influenza incidence, case characteristics, types and subtypes of circulating influenza virus in the Nacional Profesor Alejandro Posadas Hospital were studied, and were compared to incidences during 2009-2012. From late May to the end of August 2013 (EW18-35), an increase was observed in the proportion of patients' visits for respiratory disease, influenza-like illness and hospitalizations due to pneumonia; of 207 cases diagnosed with influenza A virus, 153 were infected by H1N1pdm09, 46 by H3, and eight without subtype. The highest proportion of cases was found in children under five years of age, followed by the group 60-64. The chances of having the illness were three times greater among the group 40-64 years old compared to 15-39 or those older than 64. Mortality, which increased with age, was 7.2%, and the odds of death were six times higher among those older than 64. Vaccination rate among the cases was 11.6%. None of the fatal cases had received the vaccine. After the 2009 pandemic, the proportions of annual patients' visits decreased until 2012; in 2013, an increase of 52.0% during the winter period compared to 2012. The viral circulation started earlier in 2013 compared to previous years. FLU-A(H1N1pdm) was the predominant circulating virus in 2009 and 2013, FLU-A(H3) in 2011, FLU-A(H3) and FLU-B in both 2010 and 2012.