*AZ, AR, CA, CO, CT, FL, IL, MO, NY, OH, OR, PA, SC, VT, VA, WI **Preliminary data reported to CDC. Mumps outbreaks are not reportable.

* Case count is preliminary and subject to change.

**Cases as of January 31, 2019. Case count is preliminary and subject to change.

Source: Morbidity and Mortality Weekly Report (MMWR), Notifiable Diseases and Mortality Tables

Mumps Cases

From January 1 to January 25, 2020, 16 states* in the U.S. reported mumps infections in 70** people to CDC.

Before the U.S. mumps vaccination program started in 1967, about 186,000 cases were reported each year, but the actual number of cases was likely much higher due to underreporting. Since the two-MMR dose vaccination program was introduced in 1989, U.S. mumps cases decreased more than 99%, with only a few hundred cases reported most years. However, since 2006, there have been several increases in cases and outbreaks (see below).

Outbreaks

Mumps outbreaks can still occur in U.S. communities of people who previously had one or two doses of MMR vaccine. This is particularly common in close-contact settings. High vaccination coverage helps limit the size, duration, and spread of mumps outbreaks.

From 2015 to 2017, the U.S. saw a range of different mumps outbreak settings and sizes. Cases started to increase in late 2015. From January 2016 to June 2017, health departments reported 150 outbreaks (9,200 cases), including households, schools, universities, athletics teams and facilities, church groups, workplaces, and large parties and events. The largest outbreak occurred in a close-knit community in northwest Arkansas that resulted in nearly 3,000 cases. Two large outbreaks from Iowa and Illinois each involved several hundred university students. About half of outbreaks involved greater than 10 cases.

From 2009 to 2010, two large outbreaks occurred. One outbreak involved over 3,000 people and mostly affected students who were part of a close-knit religious community in New York City and attended schools in which they participated in activities that involved very close contact. The outbreak started when an infected student returned from the United Kingdom where a large mumps outbreak was occurring. The second outbreak involved about 500 people, mostly school-aged children, in the U.S. Territory of Guam.

In 2006, the United States experienced a multi-state mumps outbreak involving more than 6,500 reported cases. This resurgence predominantly affected college-aged students living in the Midwest, with outbreaks occurring on many different Midwestern college campuses.

For more information about mumps outbreaks see Mumps Outbreak Articles.

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