Background: Human metapneumovirus (HMPV) is considered an important respiratory pathogen in young children. To gain insight into the seasonality and epidemiologic characteristics of HMPV infection, this study determined the frequency of HMPV infections in hospitalized infants during a 7-year period.
Methods: By use of real-time reverse-transcriptase polymerase chain reaction, nasopharyngeal aspirates from 1612 infants less than 2 years of age who were hospitalized for acute respiratory tract illness were tested for the presence of HMPV. Weekly HMPV testing data were analyzed to assess the timing of HMPV activity. Season variability was estimated by comparing the onset, duration, peak, and end of outbreaks from October 2000 through October 2007.
Results: Overall, 109 (6.8%) of 1612 cases of acute respiratory illness were associated with HMPV infection. Seasonal HMPV activity varied substantially from year to year, both in prevalence rates of HMPV cases and in seasonal timing of outbreaks. HMPV activity was characterized by a biennial rhythm, with spring seasons occurring every second year, and these accounted for a substantial proportion, up to 30%, of hospitalized cases of acute respiratory tract illness.
Conclusions: HMPV activity varies substantially from year to year, both in the frequency and timing of illness and shows a biennial pattern of alternating winter and spring activity.