The burden of human metapneumovirus (HMPV) in young children at various locations in the United States is unknown. A prospective, population-based surveillance study looking at children under 5 years of age admitted to hospitals with acute respiratory illness in the counties around Nashville, TN., Cincinnati, and Rochester, N.Y. during the winters of 2003 through 2009 is summarized herein. Children with low white blood cell counts from chemotherapy were not studied.
Clinical data were obtained from parents and medical records. Children under five with coughing, wheezing, or fever within 48 hours of admission, or during outpatient or emergency department (ED) visits, were tested for HMPV by a PCR assay. The incidence of HMPV detection in symptomatic pediatric hospitalization and outpatient visits was recorded.
HMPV infection was found in 6% of hospitalized children (200 of 3490 symptomatic admissions). HMPV-positive children were diagnosed with pneumonia more often than HMPV-negative children (N=99 or 50%, vs. N=731 or 22%; P
Since they had pneumonia, children under 5 years of age with HMPV required more chest x-rays, supplemental oxygen therapy, and stayed longer in the intensive care unit than children without HPMV infection.
HMPV was found in 7% of children in outpatient clinics (222 of 3257), and seven percent of children in the emergency department (221 of 3001) were also found to be positive for HMPV, while it was detected in only 1% of controls (children tested during well-child check-ups).
The annual rate of hospitalization associated with HMPV infection was 1 admission per 1000 children less than 5 years of age, 2 admissions per 1000 children aged 6 to 11 months, and 3 admissions per 1000 infants less than 6 months of age.
Annual outpatient visits associated with HMPV were estimated to be 55 clinic visits per 1000 children under 5 years of age, and 13 ED visits were projected per 1000 children annually. 
Symptoms of pediatric HMPV include coughing, rhinitis, fever, wheezing, and laryngitis. Acute otitis media (AOM or acute middle ear infection) was the complication seen in 61% of children under the age of 3 years with HMPV. 
Most HMPV-positive inpatient and outpatient children have no underlying medical conditions, except inpatients more often have a history of premature birth and asthma. HMPV ran a more severe course in children who had neutropenia (low white blood cell count) due to chemotherapy, with some mortality risk. 
Children in the first five years of life, living in the counties of Davidson in Tennessee, Hamilton in Ohio, and Monroe in New York, had increased rates of hospital admissions and pneumonia when infected by human metapneumovirus (HMPV), a virus discovered in 2001, and now known to be global in scope.  A history of premature birth or asthma predisposes a child to HMPV infection. This study, based in the United States, reflects cases infected by the target organism, i.e. HMPV, which at times are found to have infection by other organisms, e.g. RSV, influenza virus, and others.
In good measure, this study reveals worrisome features concerning HPMV infection in young children, making consideration of vaccine development possibly worthy of further research, for this study is one of surveillance. A study with the power to ascribe causation of an illness, such as pneumonia, to an organism, i.e . HMPV, would be helpful in this regard.
 Burden of Human Metapneumovirus in Young Children, Kathryn Edwards, Yuwei Zhu, Marie Griffin, e. al., N.Engl.J.Med. 2013;368:633-43.
 Human Metapneumovirus Infections in Children, Terho Heikkinen, Riikka Österback, Ville Peltola, et al., Turku University Hospital, Turku, Finland Emerging Infectious Diseases Volume 14, Number 1-January 2008;ISSN:1080-6059.