Investigation of an outbreak of influenza A in a neonatal intensive care unit (NICU) with examination of risk factors for infection and outcomes.

Retrospective cohort study of infants admitted to the unit during the outbreak period. Prospective survey of NICU staff and mothers of infants in the cohort study.

Level III nursery in a university-affiliated tertiary referral center.

Nineteen infants in the NICU were infected with influenza A. There were six symptomatic cases and one death who had evidence of virus-associated hemophagocytic syndrome at autopsy. Amantadine prophylaxis was offered to the NICU staff, and amantadine therapy was given to five of the six symptomatic infants. Mechanical ventilation, gestational age, birth weight, Clinical Risk Index for Babies score, and twin pregnancy were associated with acquisition of influenza A on univariate analysis. Mechanical ventilation (odds ratio [OR], 6.2; P=.02) and twin pregnancy (OR, 7.0; P=.04) remained as significant risk factors for infection on multiple logistic regression analysis. Only 15% of respondents to the NICU staff survey were vaccinated against influenza. There was no association between a history of an influenza-like illness during pregnancy and acquisition of influenza A by infants of mothers who responded to the maternal survey (OR, 0.91; P=1.0).

Influenza A is an important pathogen in the neonatal population and is readily transmissible in the NICU setting.