Virological and clinical characterization of respiratory infections in children attending an emergency department during the first autumn-winter circulation of pandemic A (H1N1) 2009 influenza virus.

To characterize respiratory virus infections during the first autumn-winter season of pandemic A (H1N1) 2009 influenza virus (A/H1N1/2009) circulation, a prospective study in children attending a paediatric emergency department at the Sapienza University hospital, Rome, was conducted from November 2009 to March 2010. By means of both nasal washings and pharyngeal swabs, enrolled children were checked for 14 respiratory viruses. The majority of acute respiratory infections resulted from viral pathogens (135/231, 58%). Overall, the most common was respiratory syncytial virus (RSV), in 64% of positive samples; A/H1N1/2009 was the only influenza virus found in 16% and rhinovirus (RV) in 15%. Virus-positive children did not differ significantly from virus-negative children in signs and symptoms at presentation; of the virus groups, RSV-infected children were younger and more frequently admitted to intensive-care units than those infected with A/H1N1/2009 and RV. Of the hospitalized children, stratified by age, both infants and children aged >1 year with RSV were most severely affected, whereas A/H1N1/2009 infections were the mildest overall, although with related pulmonary involvement in older children. Children with RV infections, detected in two flares partially overlapping with the A/H1N1/2009 and RSV peaks, presented with bronchiolitis, wheezing and pneumonia. Leukocytosis occurred more frequently in RV-infected and A/H1N1/2009-infected children, and numbers of blood eosinophils were significantly elevated in RV-infected infants. Given the fact that clinical and epidemiological criteria are not sufficient to identify viral respiratory infections, a timely virological diagnosis could allow different infections to be managed separately.