Epidemiological and molecular surveillance of influenza and respiratory syncytial viruses in children with acute respiratory infections (2004/2005 season)

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Objective. During the 2004/2005 influenza season an active virological surveillance of influenza viruses and respiratory syncytial virus (RSV) was carried out to monitor the epidemiologic trend of acute respiratory infections (ARI) in the paediatric community. Materials and methods. 100 patients (51 males, 49 females; mean age: 19 months), either treated at the Emergency Unit or hospitalized in the Pediatric Unit of “San Carlo Borromeo Hospital” (Milan), reporting symptoms related to ARI were enrolled. Pharyngeal swabs were collected for virological investigation by: 1) multiplexnested- PCR for the simultaneous identification of both influenza A and B viruses and RSV; 2) multiplex-nested- PCR for the subtyping of influenza A viruses (H1 and H3). Results. 12% (12/100) subjects were infected with influenza A virus, 4% (4/100) with influenza B virus and 14 (14%) with RSV. Of all the 12 influenza A positive samples 4 (33.3%) belonged to subtype H1 and 8 (66.7%) to subtype H3. Bronchiolitis and bronchitis episodes were significantly higher among RSV-infected subjects than among influenza- infected subjects (42.8% vs 6.2%; p<0.05 and 35.7% vs 6.2%; p<0.05, respectively). Pneumonia episodes occurred similarly both in influenza-infected children and in RSV-infected ones. Conclusions. During the 2004/2005 influenza season, influenza viruses and RSV were liable for high morbidity among paediatric subjects.The present study underlies the importance of planning an active surveillance of respiratory viral infections among paediatric cases requiring hospitalization due to ARI.A thorough analysis of target population features, of viruses antigenic properties and seasonality will be decisive in the evaluation of each clinical event.