Acute bronchiolitis: Influence of viral co-infection in infants hospitalized over 12 consecutive epidemic seasons

Bronchiolitis is the first lower respiratory tract viral infection manifesting in infants younger than 12 months of age. Our aim was to evaluate clinical and serological differences in infants with bronchiolitis from a single or from multiple viruses. Our secondary aim was to investigate differences in recurrent wheezing episodes after 12-24-36 months of follow-up. We reviewed the clinical records for 486 full-term infants hospitalized for bronchiolitis with at least one virus detected in the nasopharyngeal aspirate. In 431 (88.7%) patients one virus was detected and in 55 (11.3%) infants more than one virus was found. No differences were observed in the length of hospitalization, clinical severity score, O-2 supplementation or admission to the intensive care unit. Single virus was associated with higher serum C-reactive protein (C-RP) than infants with multiple viruses and higher blood neutrophil counts. Respiratory syncytial virus (RSV) was the most frequently detected virus. RSV alone was associated with higher C-RP (P=0.007), compared to RSV coinfection. Infants with human rhinovirus (hRV) alone had higher white blood cell counts, higher blood neutrophils, and higher serum C-RP levels than hRV co-infection (P=0.029, P=0.008, P=0.008). RSV+hRV, the most frequent co-infection, was associated with lower neutrophil count and lower C-RP levels (P=0.008, P=0.016) and less fever (P=0.012), when comparing RSV versus hRV versus RSV+hRV. No differences were found in the frequency of recurrent wheezing between single versus multiple viruses after bronchiolitis. Our findings suggest that in infants with bronchiolitis multiple viral co-infections can occur, without influence in the clinical severity of the disease. Infants with co-infection seems to mount a lower inflammatory response.