Observational study of respiratory syncytial virus-associated hospitalizations and use of palivizumab in premature infants aged 29–32 weeks

Abstract

The national observational multicenter cohort study presented here was conducted over two respiratory syncytial virus (RSV) seasons (2001–2003) in Austria to collect data on RSV-related rehospitalizations in premature infants of 29 –32-weeks’ gestational age. The results revealed an overall RSV hospitalization rate of 4.5% (36/801). Risk factors were discharge from the neonatal intensive care unit between the months of October and December, birth between June and December 2002, and neurological disease. Palivizumab prophylaxis was given to 238 (29.7%) infants, and 148 infants received inadequate or incomplete courses. Respiratory syncytial virus (RSV) infection represents a major cause of rehospitalization during the first year of life in preterm infants [1]. Recommendations for RSV prophylaxis with palivizumab [2] have been adopted without major modifications in Austria [3], and they suggest that decisions regarding this drug’s administration should be based on local epidemiological data. Currently, very limited data are available on the risk of RSV-related rehospitalization in Austria [4]. Due to the fact that insurance companies allocate and reimburse prophylaxis with palivizumab in this group of premature infants differently from published recommendations and with great local variation, we initiated a nationwide observational cohort study. The study was aimed at collecting data on RSV-related rehospitalization of premature infants of 29–32-weeks’ gestational age in order to analyze associated risk factors and to assess the use of palivizumab prophylaxis in this population. Infants were included if their gestational age was between 29 (29+0) and 32 (32+6) weeks and if they were born between 1 June 2001 and 31 December 2002. All infants were followed up until 1 June 2003. For the first RSV season, data on all rehospitalizations were collected retrospectively from medical charts and by telephone calls: for the second RSV season, which occurred after the study was initiated in February 2002, data were collected prospectively. In cases of rehospitalization due to respiratory illness, the following data were collected: patient age in months, the month in which rehospitalization occurred, severity of respiratory illness (determined using the modified clinical lower respiratory illness/infection score [5]), length of stay, number of days with supplemental oxygen, number of days at the intensive care unit, and number of days with mechanical ventilation including nasal continuous positive airway pressure. RSVantigen detection was performed on nasopharyngeal aspirates using either enzyme-linked immunosorbent assays or immunofluorescence techniques. Viral cultures were not performed. Prophylaxis with monthly administered intramuscular injections of palivizumab was usually started at the end of October or beginning of November, with the last injection in March. Recommendations for prophylaxis were influenced by local differences in allocation and reimbursement of prophylaxis by the insurance companies. Prophylaxis administration was not influenced by the study protocol. The study was approved by the local ethics committee, and informed consent was given by the parents of those infants prospectively enrolled into the study. Statistical analyses were performed using the Pearson chi-square and Yate’s corrected chi-square test, as appropriate for categorical data, and the t-test and Fisher’s exact test, as appropriate for numerical data. Multivariate analysis was performed using a logistic regression model with backward elimination and the Wald criterion. Analysis was done with SPSS (SPSS, Chicago, IL, USA), and StatXact4 (Cytel, Cambridge, MA, USA) software. B. Resch (*) . W. Gusenleitner . W. D. Muller Division of Neonatology, Department of Paediatrics, Medical University Graz, Auenbruggerplatz 30, 8036 Graz, Austria e-mail: bernhard.resch@meduni-graz.at Tel.: +43-316-3852605 Fax: +43-316-3852678