Epidemiology of HMPV and Other Respiratory Viral Infections Among Outpatients, 2016-2022

Most studies of human metapneumovirus (HMPV) epidemiology have been among inpatients. This study examined the epidemiology of HMPV compared with other common viruses among outpatients seeking care for an acute respiratory illness (ARI) during 5 influenza seasons (2016-2017 to 2019-2020, before the coronavirus disease 2019 pandemic, and in 2021-2022, during the pandemic).

Outpatients ≥6 months old seeking care for ARI and presenting with cough of ≤7 days' duration provided nasal and pharyngeal swab samples, demographic data, and access to electronic medical record data. Samples were tested with reverse-transcription polymerase chain reaction assays for HMPV, influenza, parainfluenza virus (PIV) 1-4, respiratory syncytial virus (RSV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Student's t and χ² tests were used to compare HMPV cases with other ARIs.

After exclusion of 68 coinfections, 7143 patients remained; 2017 had influenza, 762 had RSV, 423 had HMPV, 83 had PIV, 352 had SARS-CoV-2, and 3506 tested polymerase chain reaction negative for all of these viruses. Of all patients with ARI each influenza season, 30.2%-37.1% tested positive for influenza, 11.3%-13.6% for RSV, 4.7%-7.3% for HMPV, and 0.1%-1.9% for PIV. Compared with patients with RSV, those with HMPV less often had congestion, dyspnea, and sore throat. Compared with patients with influenza, those with HMPV were less likely to have fever but more often had congestion or dyspnea and felt worse at 7-14-day follow-up. Children recovered from HMPV faster than adults.

HMPV is an important cause of outpatient ARI during influenza season. Patients with HMPV had slightly different demographic characteristics and symptoms from those with other ARIs.