(C-056) Incidence and Severity of Human Metapneumovirus Infection in Adult Populations: A Literature Review

Background: Infections caused by human metapneumovirus (hMPV), a part of the same family as Respiratory Syncytial Virus, have a wide range of manifestations from mild acute respiratory illness (ARI) to severe pneumonia and death. Evidence regarding the epidemiology of hMPV in adults is limited. A better understanding of the impact of this virus is needed for to support the launch of hMPV vaccines in development.

Objectives: To review the literature on hMPV infection incidence and severity in adults and evaluate differences in these outcomes by age group.

Methods: Pragmatic reviews of PubMed and EMBASE (Ovid) literature databases limited to English language and human studies were conducted separately for hMPV incidence and severity. Reports that exclusively focused on high-risk populations were not included in these reviews. Editorials, letters, and case reports were removed. Titles and abstracts were screened for eligibility, and eligible records underwent full text review.

Results: Of the 15 studies identified for the adult incidence review, 6 reports focused on the United States, the only country with multiple studies identified. Other countries represented were Australia, Canada, Guatemala, India Japan, Kenya, the Netherlands, New Zealand, and South Africa. Most studies were set before the COVID-19 pandemic period (n=13). Seven studies used cohort designs that assessed rates of detectable infection and/or ARI. The remaining studies were based on laboratory or healthcare surveillance and primarily focused on hMPV related hospitalization. Reported hMPV hospitalization rates 100,000 per person-years ranged from 0.8 to 36 in adults aged 18 to 49 years, 5.4 to 176 in those aged 50 to 64 years, and 13 to 593 in adults aged 65 years and older, although age cutoffs used were inconsistent across studies.

In the severity review, of the 35 publications identified, 4 reported on outcomes for adults including hospitalization, hypoxia, pneumonia, ICU admission, mechanical ventilation, respiratory failure and death. Only one study based outcome prevalence on age-stratified groups including more than 25 individuals each. In this study, more older adults experienced hypoxia than younger adults (79% vs 51%), whereas ICU admission was higher in younger adults (1% vs 6%).

Conclusions: The severity and burden of hMPV in adults both generally increased with age across identified reports. Additional studies of hMPV incidence and severity in adults, particularly in the post-COVID-19 pandemic years, are needed. Improved alignment of critical study design elements, such as testing practices, case definitions, age cutoffs, and outcomes measures, can assure better comparability across studies.