Introduction There is very little data available on the impact that viral respiratory tract infections (VRTIs) have on neonatal morbidity during their NICU stay.

Hypothesis NICU patients with proven VRTIs have significantly worse respiratory outcomes until the time of discharge from hospital.

Methods We conducted a retrospective case-control study, at two large UK tertiary centres, of all NICU patients with multiplex PCR confirmed VRTIs between 2007 and 2013. Two controls per case were matched for centre and gestation.

Results 255 babies (86 cases and 169 controls) were identified with a median gestation of 29 weeks (IQR 26–34) for both groups. No differences were noted between groups in birth weight, antenatal steroids, maternal smoking or number of siblings. 71% of cases had rhinovirus, 8% RSV and 6% H1N1. Fewer cases had positive blood cultures during their admission (11/86 vs 65/169, p < 0.0001). Almost half (46%) of all VRTI positive babies required escalation of respiratory support especially those <28 weeks gestation who required re-ventilation (38%). Cases required a significantly greater number of days of respiratory support (median 21 vs 7, p < 0.001 see table) and more were discharged on home oxygen (35% vs 18%, OR 2.54 95% CI 1.4–4.7, p < 0.01). Mortality did not differ between groups (3/86 and 11/169).

Discussion This is the largest study of VRTIs in this population to date and demonstrates significant respiratory morbidity with rhinovirus being the dominant pathogen. We need to explore better ways of minimising the impact of VRTIs in this vulnerable population.