Contribution of respiratory syncytial virus (RSV) among patients <15 years hospitalized with severe acute respiratory infection (SARI) in Milan, 2014-2017

Aim: Respiratory syncytial virus (RSV) infections may range from cold to severe acute respiratory infection (SARI) and are responsible for substantial pediatric morbidity. We describe the results of RSV molecular detection in respiratory samples collected from children <15 years hospitalized with SARI in Milan (Italy) during four consecutive years. Method: From January 1st, 2014, to December 31st, 2017, 3013 respiratory samples (2826 upper-respiratory-tract [UTR] and 187 lower-respiratory-tract [LTR] specimens) collected from as many children <15 years hospitalized with SARI at an University hospital in Milan were analysed. After DNA/RNA extraction, samples were tested by a multiplex real-time PCR to detect RSV and other respiratory viruses. Results: 571 (19%) respiratory samples tested RSV-positive. RSV-positivity rate by sample type was similar (URT vs LRT: 19.2% vs 14.4%; p=0.09). The median age of RSV-positive cases was 6.6 months (inter-quartile range: 17.2 months); 52.2% were males. 62.2% (355/571) of RSV-positive samples were identified in children <1 year and 12.4% (71/571) in those <1 month. RSV was detected throughout the study period; 59.2% (338/571) cases were identified during seasonal peaks (December-February). In 49.9% (285/571) of RSV-positive samples at least another virus (mainly Rhinovirus: 45.9%) was detected, particularly (60%; 171/285) in samples collected from children >1 year. Conclusions: Accordingly to other studies, RSV was detected in 19% of hospitalized-SARI cases <15 years, mainly in children <1 year and in December-February. Sampling of upper or lower airways resulted in similar RSV-positivity rate. Routine molecular testing to detect RSV is warranted to improve clinical management of pediatric patients.