Respiratory syncytial virus (RSV) in pediatric influenza-like illness
(ILI) cases in Lombardy, Northern Italy, during seven consecutive winter
seasons (from 2014-2015 to 2020-2021)
Abstract
INTRODUCTION. Respiratory syncytial virus (RSV) is the major cause of
lower respiratory tract illness in young children and can also cause
influenza-like illness (ILI). Here we investigated the epidemiological
features of RSV infection in pediatric ILI cases in Lombardy (a region
in Northern Italy accounting nearly 10-million inhabitants) from
2014-2015 to 2020-2021 winter seasons. MATERIAL AND METHODS. Data for
this study were retrieved and statistically analyzed from the database
of virological influenza surveillance of the regional reference
laboratory for Lombardy within the Italian influenza surveillance
network (InfluNet). RESULTS. RSV accounting for nearly 19% of pediatric
ILI with a risk of infection nearly 2-fold greater than that of
individuals ≥15 years. The RSV positivity rate increased to 28%
considering 0-5 years old children. Although in children ≤5 years the
risk of infection from influenza viruses resulted nearly 2-fold higher
than the risk of RSV infection, the age group 4-6 months and 7-12 months
showed 5-fold greater risk of infection from RSV than from influenza.
Children ≤5 years of age with presence of one or more comorbidities had
a nearly 5-fold greater risk of getting RSV infection than otherwise
healthy 0-5 years old children. DISCUSSION. The use of the ILI sentinel
surveillance allowed us to identify groups at higher risk of RSV and
influenza infection and to define the start, duration, timing and
intensity of the RSV and influenza community circulation, determining
thresholds based on historical data. This surveillance approach can be
implemented to assess the nearly real-time RSV circulation and impact.