Respiratory viruses and acute respiratory tract infections in children under 15 years, Milan (Italy), 2015 and 2016

BACKGROUND-AIM Acute respiratory tract infections (ARI) are a major cause of children morbidity worldwide. Viruses are the leading etiologies of ARI. We describe the results of molecular detection of respiratory viruses in samples collected from children with ARI admitted to a University and research hospital in Milan (Italy) in 2015 and 2016. METHODS 1626 respiratory specimens collected from as many children <15 years with ARI were analysed. After DNA/RNA extraction (EZ1®DSP Kit, Qiagen), samples were tested by a multiplex real-time PCR (Anyplex™ II, RV16-Detection, Seegene) to detect: Adenovirus (AdV), Bocavirus (BoV), Coronavirus (CoV), Parainfluenza virus (PIV), Metapneumovirus (MPV), Enterovirus (EV), Respiratory syncytial virus (RSV), Rhinovirus (RV), and Influenza virus (IV). RESULTS 74.9% (1218/1626) of samples were positive for at least one of the viruses included in the panel; 35.8% (436/1218) of these tested positive for more than one virus. RV, RSV and AdV were the targets most frequently detected (51.9%, 26.7% and 15%, respectively), followed by BoV (13.9%), EV (11.8%) and PIV (10.2%). CoV, IV and MPV were the viruses identified less frequently (9.8%, 8.8%, and 5.3%, respectively). AdV and EV were co-detected with other viruses in 79.8% and 68.8%, respectively. Children who tested positive for at least one virus were younger than those who resulted negative (median age: 13.1 months [IQR: 34.3 months] vs 26.8 months [IQR: 46.36 months]; p=0.03). Most (57.3%) children with positive sample were <3 years. RSV was detected mainly in infants (median age 4.4 months; [IQR: 15.2 months]) whereas IV in very young children (median age 29.7 months; [IQR: 66.3 months]). 63.2% of positive cases occurred during fall and winter. MPV and EV were detected more frequently in spring and summer. CONCLUSIONS In our ARI series, at least one virus was identified in 75% of cases, with RV and RSV being the main contributors. Viruses were identified in ARI cases throughout the year, particularly in children <3 years. In 1 out of 3 positive-samples more than one virus was detected. The routine performance of molecular assays to detect a wide range of respiratory viruses can benefit clinical management of patients and can give information on the epidemiology of these viruses.