Epidemiology of HMPV and other respiratory viral infections among outpatients, 2016-2022

Background 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 five influenza seasons (2016-2017 to 2019-2020 – pre-COVID-19 pandemic and 2021-2022 peri-COVID-19 pandemic). Methods Outpatients ≥6 months old seeking care for (ARI) presenting with cough of ≤7 days’ duration provided nasal and pharyngeal swabs, demographic data and access to electronic medical record data. Samples were tested by RT-PCR for HMPV, influenza, parainfluenza viruses 1-4 (PIV), respiratory syncytial virus (RSV) and SARS-CoV-2. Chi-square and student’s t-tests compared HMPV cases with other ARIs. Results After excluding 68 co-infections, 7,143 patients remained; 2,017 had influenza, 762 had RSV, 423 had HMPV, 83 had PIV, 352 had SARS-CoV-2 and 3,506 tested negative for any of these viruses (PCR-negative). The percentage of total ARI patients each influenza season who tested positive for influenza was 30.2%-37.1%; RSV was 11.3%-13.6%; HMPV was 4.7%-7.3%; and PIV was 0.1%-1.9%. Compared to patients with RSV, HMPV patients less often had congestion, dyspnea and sore throat. Compared to patients with influenza, those with HMPV were less likely to have fever or but more often had congestion, dyspnea, and felt worse at 7-14 day follow-up. Children recovered from HMPV faster than adults. Conclusions HMPV is an important cause of outpatient ARI during influenza season. Those with HMPV had slightly different demographic characteristics and symptoms from those with other ARI.