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.

Figure 1

Epidemic pattern of symptomatic hMPV infections in combined prospective and hospitalized cohorts during four consecutive winters.

Figure 2

Comparison of clinical presentation for hMPV (n=91), RSV (n=109) and influenza A (n=138) in hospitalized patients, exclusive of mixed viral infections. RSV and influenza data from reference 2. *, P=.006 for hMPV compared to influenza A; †, P=.06 for hMPV compared to influenza A