The impact of influenza and respiratory syncytial virus on hospitalizations for lower respiratory tract infections in young children: Slovenia, 2006-2011

Background Influenza and respiratory syncytial viruses (RSV) are important viral pathogens in childhood. Objectives Our aim was to estimate the effect of influenza and RSV on excess hospitalizations for acute lower respiratory tract infections (ALRTI) in children aged <= 5. Methods Retrospective, population-based study was performed for five seasons (2006-2011). Slovenian national hospital discharge data and surveillance data were used to estimate the effect of influenza and/or RSV on ALRTI hospitalizations (acute bronchiolitis, pneumonia, and acute bronchitis) using rate difference method. Results An excess was observed in average weekly ALRTI hospitalizations per 100 000 among children aged <= 5 in all five seasons during influenza and/or RSV active period. During three seasons, there was higher excess in ALRTI hospitalizations in the period when influenza/RSV cocirculated compared with the RSV period. In pandemic season (2009/2010), the only one without influenza/RSV overlap, excess hospitalization was higher in RSV period. The highest excess of hospitalizations was found among the youngest children (0-5 months old). In all five seasons, acute bronchiolitis was the most common ALRTI recorded in hospitalized young children. Conclusions Respiratory syncytial viruses was leading viral pathogen associated with ALRTI hospitalizations in children aged <= 5. The cocirculation of influenza virus increased the burden of ALRTI hospitalizations especially in seasons with A(H3) predominance.