Seasonal Incidence of Human Metapneumovirus in High-Risk Adults With Medically Attended Acute Respiratory Illness in a Rural US Community

Background

The burden of human metapneumovirus (hMPV) among community-dwelling high-risk adults is understudied. We calculate the cumulative incidence of outpatient hMPV in high-risk adults, over five consecutive winter respiratory virus seasons (2015–2016 through 2019–2020), and describe clinical characteristics of their illnesses.

Methods

We conducted a retrospective analysis of data and respiratory specimens from adults ≥ 18 years old originally participating in a test-negative study of influenza vaccine effectiveness. We included adults with ≥ 1 high-risk condition in 2015–2016 through 2019–2020 seasons. Residual respiratory specimens were retested for hMPV using a multiplex viral panel. We calculated seasonal incidence using Poisson regression and population weighting, with the sum of observed and extrapolated hMPV cases in the study cohort divided by the number of adults with high-risk conditions in the underlying source population.

Results

We tested 3601 respiratory samples; the mean (SD) age of individuals contributing samples was 53 (19) years. We identified 289 individuals (8.0%) with a respiratory sample positive for human metapneumovirus. The estimated seasonal incidence of outpatient hMPV-associated acute respiratory illness was 95.6 (95% CI: 80.5–113.4) cases per 10,000 high-risk adults. These values varied by season, with the highest incidence in 2015–2016 (276.8 cases per 10,000; 95% CI: 210.7–363.5) and lowest in 2016–17 (55.0 cases per 10,000; 95% CI: 31.2–97.0).

Conclusions

We identified substantial seasonal incidence of hMPV cases in community-dwelling high-risk adults in a Wisconsin population cohort.