Human metapneumovirus infections cause similar symptoms and clinical severity as respiratory syncytial virus infections

Human metapneumovirus (hMPV) is a recently discovered pathogen in respiratory tract infection. The published literature suggests milder illness severity in hMPV compared with respiratory syncytial virus (RSV) infection. In two consecutive seasons, 637 nasopharyngeal aspirates from pediatric patients were tested by hMPV polymerase chain reaction, and risk factors and clinical and laboratory items were analyzed. The hMPV patients were compared with hMPV-negative but RSV-positive patients by matched pair analysis. HMPV was detected in 17.9% of all samples. In total, 88 hMPV-infected patients with complete datasets were considered. More than half of all hMPV patients were older than 12 months, 45.5% had at least one risk factor for a severe course of viral respiratory tract infection, and 27.3% were born prematurely, 15.9% with a birth weight < 1,500 g. At least one other virus was also detected in 39 patients (44.3%; RSV in 29.5%). Coinfection did not result in greater severity of illness. On matched pair analysis (hMPV-positive/RSV-negative vs. hMPV-negative/RSV-positive), the epidemiological and clinical features of hMPV infection were similar to those of RSV infection, as in the hMPV group higher proportions of patients with hypoxemia on admission (33% vs. 21%) and of intensive care treatment (20.8% vs. 10.4%) were observed. More hMPV patients showed lobar infiltrates in radiological chest examination. In 60% of all hMPV infections, the attending physicians prescribed antimicrobial chemotherapy. We conclude that in hospitalized children, hMPV infection is as serious as RSV infection and therefore deserves the same attention. Virologic diagnosis from respiratory secretions is mandatory because clinical, laboratory, and radiological signs cannot sufficiently discriminate between viral and bacterial respiratory tract infection in infants and children.