Influenza Virus Infection in Infants Less Than Three Months of Age

Objective: We evaluated the presentation, outcomes, and the risk of serious bacterial infection (SBI) in infants <3 months old with influenza virus infection. Patients and Methods: We identified demographic, hospitalization, and microbiologic data from computerized medical records for all infants and children <24 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 those <3 months of age with older groups. Results: We identified 833 children <24 months of age with laboratory-confirmed influenza. Of those, 218 were <3 months old. Influenza accounted for 3.6% of all evaluations of febrile infants and 12% of febrile infant encounters during winter. Infants <3 months of age were less likely to have a high risk chronic medical condition, but were more likely to be hospitalized than children 3 to <24 months old (P < 0.005). Infants <3 months with influenza had fewer prolonged hospital stays than those 3 to <6 months old [P = 0.056; OR: 0.5 (0.24-1.0)] and 6 to <12 months old [P = 0.011; OR: 0.43 (0.24-0.83)]. Five (2.3%) infants <3 months old had SBI. Conclusions: Infants <3 months of age with influenza virus infection often present with fever alone. Although they are more likely to be hospitalized than those 3 to <24 months old, hospital stays are short and outcomes generally good. Infants with influenza virus infection have a low risk of concomitant SBI.