New data shows that human metapneumovirus demonstrated seasonality by beginning in the winter and lasting until spring when compared with influenza and RSV.

“This is the first published summary of [human metapneumovirus (HMPV)] national data from [National Respiratory and Enteric Virus Surveillance System (NREVSS)] and demonstrates several unique features,” Amber K. Haynes, of the division of viral diseases at the CDC, and colleagues wrote. “From 2008 to 2014, the national HMPV data suggest that HMPV seasons occur later than RSV seasons, and based on the six-season median onset, the RSV season occurred first, followed by influenza and then HMPV.”

Due to infrequent testing and low index of suspicion, there has been limited assessment of the seasonality of HMPV, the researchers wrote. In addition, the disease can cause a respiratory tract infection that is clinically identical to RSV and influenza. The researchers utilized data from NREVSS that tracks several respiratory viruses annually throughout the United States.

From 2008 to 2014, hospital and clinical laboratories reported all specimens and positive detections of HMPV, RSV and influenza to the NREVSS. The researchers defined a season as at least 3% positivity for HMPV and at least 10% positivity for RSV and influenza during a surveillance year from June through July. The researchers calculated the season, onset, offset, duration, peak and 6-season medians for each virus.

They determined that 3.6% of all specimens were positive for HMPV, 15.3% for RSV and 18.2% for influenza. Six distinct HMPV seasons occurred during the study period, with onsets ranging between November and February and offsets from April to July. Based on these seasonal medians, RSV, influenza and HMPV occurred sequentially, with season durations ranging from 21 to 22 weeks.

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