Human Metapneumovirus: Important but Not Currently Diagnosable

In 2001, van den Hoogen and colleagues (1) isolated human metapneumovirus (hMPV) from 28 children by using nasopharyngeal samples collected over 20 years. Human metapneumovirus was invisible before 2001, in part because the virus did not infect standard cell lines used to isolate respiratory virus pathogens. Five years later, we have a flurry of research activity as investigators try to establish the clinical significance of this paramyxovirus. In this editorial, I will describe the virus and its clinical effects and then address 2 relevant clinical questions: whom to test for infection and which diagnostic test to use.

Human metapneumovirus has circulated worldwide in humans for at least 50 years (1). In a macaque primate animal model, this RNA virus was excreted from 4 to 10 days following inoculation (2). The mean age of hMPV-infected children is 11.6 months (3). Respiratory tract infections associated with this virus may include a self-limited clinical illness, croup, asthma exacerbations, bronchiolitis, and pneumonia (3). Among immunologically healthy people, the exact prevalence is unknown, but several studies suggest more than 70% prevalence of antibodies to the virus (1, 4, 5) and a 6% to 25% prevalence of viral shedding during respiratory illness in the community (5-8).

Among immunocompetent hosts older than 1 year of age, hMPV is a “nuisance” virus. The time and cost required to diagnose hMPV-related respiratory tract infection in otherwise healthy people do not seem …