The impact of the H1N1 influenza pandemic on clinical presentations and viral epidemiology of acute respiratory infection in preschool children in Brazil.

We assessed the impact of the H1N1 influenza pandemic on acute respiratory infection in young children from low-income families in Brazil. Influenza (specifically H1N1) detection in acute respiratory infection quintupled during the pandemic and, during its peak, it was associated with 30% of all acute respiratory infection visits to the emergency department. H1N1 was also associated with increased risk of hospitalization and coinfection.