Effectiveness of Palivizumab against Respiratory Syncytial Virus: Cohort and Case Series Analysis.

OBJECTIVE: To measure the real-world effectiveness of palivizumab immunoprophylaxis against respiratory syncytial virus (RSV)-confirmed infection before age 2 years in a population-cohort of high-risk infants. STUDY DESIGN: Palivizumab is funded for high-risk infants in Western Australia. We used probabilistically linked administrative data encompassing RSV laboratory-confirmed infections, hospital admissions, and palivizumab dispensing records for a cohort of 24 329 high-risk infants admitted to neonatal intensive care units, born 2002-2013 with follow-up to 2015. We used a traditional cohort method with Cox proportional hazards regression and a self-controlled case series analysis to assess effectiveness of palivizumab in reducing RSV-confirmed infection by number of doses. RESULTS: From the cohort of 24 329 infants, 271 (1.1%) received at least 1 dose of palivizumab and 1506 (6.2%) had at least 1 RSV-confirmed infection before age 2 years. Using the traditional cohort approach, we found no protective association of palivizumab receipt with RSV detection (adjusted hazard ratio = 0.99 [95% CI 0.5, 1.9] for 1 dose). However, using a self-controlled case series to eliminate confounding by indication, a protective association was seen with a 74% lower RSV incidence (relative incidence = 0.26; 95% CI 0.11, 0.67) following any dose of palivizumab compared with control (nonexposed) periods. CONCLUSIONS: After accounting for confounding by indication through a self-controlled analysis, palivizumab appeared effective for reducing virologically confirmed RSV in this high-risk cohort.

Maternal Chorioamnionitis and Postneonatal Respiratory Tract Infection in Ex-Preterm Infants.

OBJECTIVE: To assess whether exposure to histologically confirmed chorioamnionitis (ie, histologic chorioamnionitis [HCA]) is associated with altered risk of infection-related hospitalization (IRH) during the first 24 months of life in very preterm infants. STUDY DESIGN: This single-center retrospective cohort study analyzed data on 1218 infants born at <30 weeks gestational age (GA). Semiquantitative placental histology, obstetric, and neonatal data were extracted from hospital databases and linked with discharge diagnoses on rehospitalization until age 24 months from statewide statutory data. The associations between HCA and overall and clinical categories of IRH were analyzed by Cox proportional hazards regression with left-truncated failure times. RESULTS: Mean GA was 27 weeks, and HCA was present in 577 placentas (47.4%). Among the 1088 infants surviving until the birth-related discharge, 684 (62.9%) of had at least 1 IRH by age 24 months, of whom 287 included a diagnosis of acute lower respiratory tract infection (ALRTI). Following adjustment for sex, birth weight z-score, GA, early-onset sepsis, late-onset sepsis, previous antibiotic use, age at birth-related discharge, and chronic lung disease, HCA was associated with a 32% increased risk of hospitalization with ALRTI (HR, 1.32; 95% CI, 1.02-1.70; P = .033). There was no association with infection overall or with other infection categories. CONCLUSIONS: HCA is associated with a significantly increased risk of hospitalization with ALRTI that is independent of known risk factors, including chronic lung disease.