Epidemiology of Symptomatic Human Metapneumovirus Infection in the CASCADIA Community-Based Cohort - Oregon and Washington, 2022-2024.

Human metapneumovirus (hMPV) is an important cause of respiratory illness. However, information about hMPV incidence, patient characteristics, and symptoms outside hospital settings is limited. During June 2022-March 2024, participants aged 6 months-49 years who were enrolled in the CASCADIA community-based cohort study submitted weekly illness surveys and nasal swabs, and completed follow-up illness surveys. Swabs collected 0-3 days before reporting new or worsening symptoms were tested for hMPV and other respiratory viruses by multiplex polymerase chain reaction. Incidence was analyzed using an exponential survival model. Among 3,549 participants, 306 had symptomatic hMPV infection, representing an average of 7.5 cases per 100 persons per year (95% CI = 6.7-8.4). Incidence was highest during January-March (adjusted hazard ratio [aHR] = 4.3; 95% CI = 3.0-6.0) compared with October-December, and among those aged 2-4 years (aHR = 5.8; 95% CI = 3.8-9.0) compared with those aged ≥40 years. The most frequently reported symptoms were cough (80.4%) and nasal congestion (71.9%). Among 252 (82.4%) participants who completed a post-illness follow-up survey, 68 (27.0%) missed work, school, or child care facility attendance. Together, these findings indicate that hMPV is a common cause of respiratory illness during late winter to spring, particularly among young children, and frequently disrupts daily activities. Understanding hMPV epidemiology can guide surveillance definitions, clinical testing, and prioritization of prevention strategies.