Characteristics of reported mumps cases in the United States: 2018–2023.

• There has been a substantial decline in confirmed mumps cases since 2020. • PCR testing decline and IgM testing uptake present reporting challenges. • Only 9 outbreak-associated cases of mumps reported from 2021 to 2023. • 3% of mumps cases were imported, suggesting mumps remains endemic in the US. • Maintaining high MMR coverage is important to prevent future outbreaks. This paper highlights recent clinical complications of mumps reported in the United States and summarizes appropriate confirmatory testing for mumps, encouraging vigilance for mumps disease, an endemic vaccine-preventable illness. Surveillance data from jurisdictions reporting confirmed and probable cases of mumps in the United States were descriptively analyzed to assess epidemiologic trends from January 1, 2018 – December 31, 2023. Data were reported to the National Notifiable Disease Surveillance System and the Epidemiology and Laboratory Capacity Project O. Cases were classified according to the Council of State and Territorial Epidemiologists 2011 mumps case definition. From 2018–2023, United States health departments reported 8,006 confirmed and probable mumps cases to the National Notifiable Disease Surveillance System, of which 85.4% occurred during January 1, 2018–April 4, 2020 and 14.6% during April 5, 2020–December 31, 2023. The incidence of mumps was highest among those aged 18–24 years during 2018–2020 (maximum of 4.54 cases per 100,000 persons in 2019), and highest among those aged 1–4 years during 2021–2023 (maximum 0.67 per 100,000 persons in 2023). Incidence among all age groups during 2021–2023 remained below levels during 2018–2020. Fewer than 12% of mumps cases were confirmed during 2021–2023, compared to >50% during 2018–2019. Although incidence has declined since the COVID-19 pandemic, these surveillance data highlight that mumps remains endemic in the United States. Therefore, maintaining high MMR vaccination coverage is essential to prevent future vaccine-preventable outbreaks and minimize severe complications from infection. [ABSTRACT FROM AUTHOR]