Epidemiology of RSV and hMPV in Belgium: a 10-year follow-up.

: Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) are important respiratory pathogens. Both viral pathogens have similar clinical manifestations. The epidemiology of RSV is well known, that of hMPV is less clear. We reviewed the results of 10 consecutive years of molecular testing for RSV and hMPV in respiratory samples of Flemish patients. : In the laboratory of the OLV hospital Aalst, Belgium, multiplex RT-PCR assays are used for the detection of RSV and hMPV. The lab receives invasive and noninvasive respiratory samples of patients from all over Flanders. : Between September 2006 and August 2016, 16,826 respiratory samples were analyzed for RSV and hMPV. Of these samples, 18% tested positive for RSV and 7.3% for hMPV. RSV consistently peaked in November/December each year within a very narrow time frame. The occurrence of hMPV was less predictable and spreaded more widely throughout the winter and spring. Both viruses were mainly found in samples from young children. RSV was most frequently detected in samples from infants <3 months, while hMPV peaked between 6 and 9 months. After the age of 1 year, RSV rapidly dropped. hMPV dropped a little later and slower. Both viruses slightly increased again at older age (>50 years). : Despite their similarities, some of the epidemiologic characteristics of hMPV and RSV differ. The most striking difference is the annual distribution of RSV and hMPV infections.