title: Human Metapneumovirus Circulation in the United States, 2008 to 2014.
abstract: Human metapneumovirus (HMPV) infection causes respiratory illness, including bronchiolitis and pneumonia. However, national HMPV seasonality, as it compares with respiratory syncytial virus (RSV) and influenza seasonality patterns, has not been well described.
  
  
  
  Hospital and clinical laboratories reported weekly aggregates of specimens tested and positive detections for HMPV, RSV, and influenza to the National Respiratory and Enteric Virus Surveillance System from 2008 to 2014. A season was defined as consecutive weeks with ≥3% positivity for HMPV and ≥10% positivity for RSV and influenza during a surveillance year (June through July). For each virus, the season, onset, offset, duration, peak, and 6-season medians were calculated.
  
  
  
  Among consistently reporting laboratories, 33 583 (3.6%) specimens were positive for HMPV, 281 581 (15.3%) for RSV, and 401 342 (18.2%) for influenza. Annually, 6 distinct HMPV seasons occurred from 2008 to 2014, with onsets ranging from November to February and offsets from April to July. Based on the 6-season medians, RSV, influenza, and HMPV onsets occurred sequentially and season durations were similar at 21 to 22 weeks. HMPV demonstrated a unique biennial pattern of early and late seasonal onsets. RSV seasons (onset, offset, peak) were most consistent and occurred before HMPV seasons. There were no consistent patterns between HMPV and influenza circulations.
  
  
  
  HMPV circulation begins in winter and lasts until spring and demonstrates distinct seasons each year, with the onset beginning after that of RSV. HMPV, RSV, and influenza can circulate simultaneously during the respiratory season.
authors.affiliation: Divisions of Viral Diseases, and ahaynes1@cdc.gov.
authors.forename: Amber K
authors.initials: AK
authors.lastname: Haynes
authors.affiliation: Influenza, National Center for Immunization and Respiratory Diseases, and.
authors.forename: Ashley L
authors.initials: AL
authors.lastname: Fowlkes
authors.affiliation: Divisions of Viral Diseases, and.
authors.forename: Eileen
authors.initials: E
authors.lastname: Schneider
authors.affiliation: Divisions of Viral Diseases, and.
authors.forename: Jeffry D
authors.initials: JD
authors.lastname: Mutuc
authors.affiliation: Office of Advanced Molecular Detection, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Armstrong
authors.affiliation: Divisions of Viral Diseases, and.
authors.forename: Susan I
authors.initials: SI
authors.lastname: Gerber
mesh_terms: D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification; D007251:Influenza, Human / Q000453:epidemiology; D029121:Metapneumovirus / Q000302:isolation & purification*; D018184:Paramyxoviridae Infections / Q000453:epidemiology*; D016133:Polymerase Chain Reaction; D011159:Population Surveillance; D018357:Respiratory Syncytial Virus Infections / Q000453:epidemiology; D012136:Respiratory Syncytial Viruses / Q000302:isolation & purification; D012621:Seasons; D014481:United States / Q000453:epidemiology