Human metapneumovirus pneumonia in children: results of an Italian study and mini-review.

Human metapneumovirus (hMPV) is a newly identified paramyxovirus causing lower respiratory tract infections (LRTI). Current knowledge on hMPV is mainly based on retrospective studies performed in stored respiratory and serum samples. We found 15 previous prospective clinical studies on LRTI (11 clinical and 4 epidemiological studies) that have been reviewed. Our aims were to analyse the role of hMPV in community acquired pneumonia (CAP) and the seroconversion rate to hMPV in a prospective study in North Italian children. During a 15-month study period, 124 children were admitted due to presumptive CAP and, in 116 of them, CAP was radiologically confirmed. The aetiology of CAP was assessed by serology to 15 microorganisms, including enzyme immunoassay to hMPV. hMPV infection was found in 5 children (4.9%), being single in 2 and mixed in 3 cases. The seroconversion rate to hMPV increased with age, reaching nearly 100% seropositivity rate at school age. In conclusion, hMPV caused 0% to 17.5% of LRTI cases in children in the mini-review. The figure was about 5% in the present and in the only earlier paediatric CAP study. Thus, hMPV is a real but rare cause of paediatric CAP, although seroconversion to hMPV in most children takes place in early childhood.