Molecular characterization of respiratory syncytial viruses infecting children reported to have received palivizumab immunoprophylaxis

BACKGROUND: Respiratory syncytial virus (RSV) is a major cause of respiratory infections in children. Palivizumab (PZ) is the only RSV-specific immunoprophylaxis approved by the U.S. Food and Drug Administration. Mutations leading to amino acid substitutions in the PZ binding site of the RSV F protein have been associated with breakthrough RSV infections in patients receiving PZ. OBJECTIVE: To detect PZ resistance conferring mutations in RSV strains from children who received PZ. STUDY DESIGN: Children aged ≤24 months on October 31 who were hospitalized or had outpatient visits for respiratory illness and/or fever during October–May 2001–2008 in 3 US counties were included. PZ receipt was obtained from parent interviews and medical records among children subsequently infected with RSV. Archived nasal/throat swab specimens were tested for RSV by real-time RT-PCR. The coding region of the PZ binding site of the RSV F protein was sequenced using both Sanger and pyrosequencing methods. RESULTS: Of 8762 enrolled children, 375 (4.3%) were tested for RSV and had a history of PZ receipt, of which 56 (14.9%) were RSV-positive and 45 of these had available archived specimens. Molecular typing identified 42 partial F gene sequences in specimens from 39 children: 19 single RSV subgroup A, 17 subgroup B and 3 mixed infections. Nucleotide substitutions were identified in 12/42 (28.6%) RSV strains. PZ resistance mutations were identified in 4 (10.2%) of the 39 children, of which one had documented PZ receipt. CONCLUSIONS: Although RSV PZ resistance mutations were infrequent, most RSV-associated illnesses in children with a history of PZ receipt were not due to strain resistance.