Influenza Virus Infection in Infants Less Than Three Months of Age

We evaluated the presentation, outcomes, and the risk of serious bacterial infection (SBI) in infants3 months old with influenza virus infection.We identified demographic, hospitalization, and microbiologic data from computerized medical records for all infants and children24 months of age, with laboratory confirmed influenza infection cared for at a tertiary care children's hospital during 4 winter seasons (2004-2008). We compared those3 months of age with older groups.We identified 833 children24 months of age with laboratory-confirmed influenza. Of those, 218 were3 months old. Influenza accounted for 3.6% of all evaluations of febrile infants and 12% of febrile infant encounters during winter. Infants3 months of age were less likely to have a high risk chronic medical condition, but were more likely to be hospitalized than children 3 to24 months old (P0.005). Infants3 months with influenza had fewer prolonged hospital stays than those 3 to6 months old [P = 0.056; OR: 0.5 (0.24-1.0)] and 6 to12 months old [P = 0.011; OR: 0.43 (0.24-0.83)]. Five (2.3%) infants3 months old had SBI.Infants3 months of age with influenza virus infection often present with fever alone. Although they are more likely to be hospitalized than those 3 to24 months old, hospital stays are short and outcomes generally good. Infants with influenza virus infection have a low risk of concomitant SBI.