Assessment of the International Risk Scoring Tool for Identifying Moderate-to-Late Preterm Infants at Greatest Risk of Severe Respiratory Syncytial Virus Infection Using Data From Singapore

Background: The International Risk Scoring Tool (IRST) uses three risk factors (birth 3 months before to 2 months after the respiratory syncytial virus (RSV) season start date; smoking in the household and/or smoking while pregnant; siblings and/or daycare attendance) to categorise the risk of RSV hospitalisation (RSVH) in 32-35 weeks’ gestational age (wGA) infants. Risk factor data from countries predominantly located in the Northern Hemisphere were used to build and validate the IRST. We undertook the first assessment of the applicability of the IRST in moderate-to-late preterm infants in Singapore. Method: Retrospective risk factor data were assembled in one Singaporean hospital for healthy 32–35 wGA infants without comorbidities who had RSVH in the first year of life (cases) and chronologically and gestationally age-matched controls without RSVH. Data collected included the three validated IRST risk factors, wGA, plus one additional factor, breastfeeding (defined as exclusive and given or planned from birth to 3 months of age), that was considered important in the determination of RSVH in Singapore. Predictive accuracy for RSVH was assessed by calculating the area under the receiver operating characteristic curve (AUROC). Results: Data on 50 cases and 30 controls were collected. A risk scoring tool (RST) combining maternal smoking plus other smokers in the household plus siblings plus daycare resulted in an AUROC of 0.695. Adding wGA to the RST increased the AUROC to 0.715. Substituting wGA for the risk factor of breastfeeding, however, did not improve the predictive accuracy of the RST (AUROC 0.702). The most predictive RST for RSVH included maternal smoking combined with other smokers in the household plus siblings plus daycare plus wGA plus breast feeding, which generated an AUROC of 0.730 (Figure). Conclusion: This analysis supports that the IRST is predictive of RSVH in Singaporean moderate-to-late preterm infants and that breastfeeding should be additionally included as a risk factor. Consideration should be given to substituting chronological age with wGA, as the RSV seasonality is known to be variable in Singapore. A localised version of the IRST may provide a mechanism to target existing and new monoclonal antibodies to 32–35 wGA Singaporean infants who are most likely to benefit from RSV prophylaxis.