Human respiratory syncytial virus and other viral infections in infants receiving palivizumab

BACKGROUND: Palivizumab is a humanized monoclonal antibody that prevents severe human respiratory syncytial virus (HRSV) infections. OBJECTIVES: We determined the etiology of respiratory viral infections in palivizumab recipients, and monitored the clinical outcome and HRSV genotype in HRSV-infected infants. STUDY DESIGN: Nasopharyngeal aspirates (NPAs) were collected from children receiving palivizumab who consulted or were hospitalized for acute respiratory tract infection (ARTI) during the 2004–2005 season. Viral cultures and multiplex RT-PCR for influenza A/B, HRSV and human metapneumovirus were performed. The fusion (F) gene of HRSV amplicons was also sequenced. RESULTS: Among 116 enrolled patients, 51 (44%) had ≥1 episode of ARTI for a total of 93 visits. At least one virus was identified in 33 (36%) of the 93 NPA samples; HRSV accounted for 11 (33%) of confirmed viral etiologies. Compared to subjects who had other viral ARTI, HRSV-positive subjects had less fever (p = 0.01) and tended to have more bronchiolitis (p = 0.07). Ten subjects (11 visits) developed HRSV infection, although only one was hospitalized. HRSV was detected after a median of 5.5 palivizumab doses and a median of 14 days after the last dose. One of the 11 HRSV strains tested had a F mutation located in the palivizumab-binding site. CONCLUSION: HRSV is still a major cause of ARTI in children receiving palivizumab, although the outcome of infected children appears mild.