Human Metapneumovirus in the Community: How Often It Strikes, Whom and When

Human metapneumovirus (hMPV) causes respiratory illness in children and adults and many hospitalizations worldwide. But doctors rarely test for it, treatment is only supportive, there is no approved vaccine or treatment in the United States (several are in development), and little was known about how often it makes people ill outside health care settings.

The CASCADIA study followed Oregon and Washington residents aged 6 months to 49 years, favouring whole households, from June 2022 to March 2024. Participants sent in weekly nasal swabs and weekly illness surveys; swabs linked to a new illness were tested for hMPV and other respiratory viruses. A symptomatic infection was new or worsening symptoms reported 0–3 days after an hMPV-positive swab.

Who took part

3,549 people, followed for a median of 1.3 years (4,072 person-years in all). Median age at enrolment was 17; 58.4% were female, 70.3% non-Hispanic White, 69.0% had household incomes of $100,000 or more, and 93.2% lived in households of three or more.

How common

There were 306 symptomatic infections — 221 in children, 85 in adults. 60.8% were hMPV alone; 39.2% came with another pathogen. Nobody was infected twice.

Monthly symptomatic human metapneumovirus cases and incidence, CASCADIA cohort, Oregon and Washington, June 2022–March 2024. CDC / MMWR

Compared with adults 40 and older, the risk was about 5.8 times as high at ages 2–4, 3.7 at 6–23 months, 3.1 at 5–11 and 2.0 at 12–17. Compared with October–December, it was 4.3 times as high in January–March and lower in July–September (0.4).

It clusters in households. Of 293 infections in homes with several members taking part, 101 (34%) came within 7 days of another case in the same home. Underlying health conditions and household size were not linked to getting sick.

What it felt like

• Cough (80.4%), nasal congestion (71.9%), sore throat (38.6%) and shortness of breath (7.2%) — signs that it reaches both upper and lower airways.
• Children were more likely than adults to have cough and fever, and less likely to report congestion, sore throat, fatigue or aches.
• Of 252 people who answered a 14-day follow-up, 68 (27.0%) missed work, school or child care, 17 (6.8%) sought medical care, and 2 went to a hospital or emergency department.

What it means

hMPV is a common late-winter-to-spring respiratory illness, especially in young children, and even mild cases disrupt daily life. The overall rate matches other population studies, which mostly looked at particular ages or at medically attended illness. hMPV is a leading cause of severe respiratory illness in young children and older adults, and children's hospitalization rates are comparable to influenza's; children under 2 may be hospitalized more because they are more prone to severe disease. Lower incidence in early 2024 than in 2023 may fit reports of a two-year cycle.

More testing for hMPV could open the way to infection control and better surveillance, and knowing its burden can guide vaccines, antibodies, antivirals and other prevention.

Limits

• Follow-up was under 24 months; April–June appears only for 2023, and seasons may have shifted after the COVID-19 pandemic.
• Not every household member enrolled, and some infections have no symptoms, so household spread may be underestimated; missed swabs or test sensitivity may have missed cases.
• Finding hMPV does not prove it caused an illness, though it usually does.
• Younger infants and older adults were not included, and participants may not represent the U.S. population.

Sources

Based on Shakya M, Chu HY, Englund JA, et al., "Epidemiology of Symptomatic Human Metapneumovirus Infection in the CASCADIA Community-Based Cohort — Oregon and Washington, 2022–2024," MMWR Morbidity and Mortality Weekly Report, volume 74, Centers for Disease Control and Prevention; a work of the United States government in the public domain.