title: Human metapneumovirus infections in adults: another piece of the puzzle.
abstract: BACKGROUND
  Each winter respiratory viruses account for a significant proportion of serious respiratory illness, including hospitalization, in older adults and those with underlying medical conditions. We describe the incidence and clinical impact of human metapneumovirus (HMPV), a newly identified virus, in adults.
  
  
  METHODS
  Infection with HMPV was identified in 3 prospectively enrolled adult cohorts (young persons 19-40 years old, healthy adults > or =65 years old, and high-risk adults) and a hospitalized cohort for 4 consecutive winters (November 15 through April 15 for the years 1999 through 2003). The incidence and clinical impact were compared with those of influenza A and respiratory syncytial virus infection in the same groups.
  
  
  RESULTS
  Using reverse transcriptase-polymerase chain reaction and serologic testing, we identified HMPV infection in 2.2% to 10.5% of the 3 prospectively followed-up outpatient cohorts annually. Asymptomatic infection was common, accounting for at least 38.8% of infections in each of the cohorts. Symptoms, when they occurred, were typical of an upper respiratory tract illness, although a few high-risk persons required hospitalization. Among 1386 hospitalized patients, HMPV was identified in 8.5% (range, 4.4%-13.2%), depending on the year. Dual viral infection was identified in 22.9%. Wheezing was frequent (80%) and more common than with influenza. Twelve percent required intensive care unit admission and 11% ventilatory support, rates similar to those for influenza and respiratory syncytial virus infection.
  
  
  CONCLUSIONS
  In adults of all ages, HMPV is a common infection, and, although often asymptomatic, it can result in serious infection that requires hospitalization. Like influenza A and respiratory syncytial virus, HMPV is also a major contributor to the burden of wintertime respiratory illnesses in older adults.
authors.affiliation: Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA. Edward.walsh@viahealth.org
authors.forename: Edward E
authors.initials: EE
authors.lastname: Walsh
authors.forename: Derick R
authors.initials: DR
authors.lastname: Peterson
authors.forename: Ann R
authors.initials: AR
authors.lastname: Falsey
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D029121:Metapneumovirus; D008875:Middle Aged; D018184:Paramyxoviridae Infections / Q000175:diagnosis / Q000453:epidemiology*; D011446:Prospective Studies; D055815:Young Adult