The impact of H1N1 influenza on acute respiratory infection in pre-school children in north east brazil

Introduction Acute respiratory infection (ARI) is a major cause of mortality and morbidity in children, particularly in the developing world. In June 2009 the WHO declared a new strain of swine-origin H1N1 influenza virus as a pandemic. The aim of this study was to assess the impact of H1N1 on ARI presentations to A&E in preschool children over a year in a resource-poor setting in Brazil. Methods Children Results Samples were collected from 223 children from a resource-poor setting. 57% (127/223) were subsequently hospitalised and at least one pathogen was detected in 91.5% (204/223) of samples. The most commonly detected pathogens were Adenovirus (36%; n=80), Bocavirus (35%; n=78), Respiratory Syncytial Virus (18%; n=41), Rhinovirus (18%; n=41) and Influenza (15%; n=34). Influenza cases peaked during November 2009 with 79% (27/34) being H1N1 subtype. Co-infection was found frequently with 50% (111/223) participants being found positive for more than one pathogen. Co-infection with H1N1 was particularly common (78%) with Adenovirus and Bocavirus being the most common pathogens co-detected. Children with H1N1 infection were more likely to be admitted to hospital than those without H1N1 infection (78 vs 54%; p=0.021). At its peak, H1N1 was detected in approximately 20% of preschool children recruited to this study and attending A&E with ARI. Conclusions We have described particularly high rates of pathogen detection (91.5%) and co-infection (50%) compared to the published literature. Over the year, H1N1 was the fifth commonest virus detected. H1N1 had a significant impact given that it was detected in 20% of hospitalised preschool children with ARI during the pandemic peak.