Mumps is highly infectious and spreads through congregate living/social settings causing sporadic outbreaks as has been demonstrated in recent outbreaks in the U.S.
In LA County and surrounding areas, there is currently a mumps outbreak involving over 40 patients. The majority of these cases are among MSM but some are women and heterosexual men with social connections to MSM cases. Most transmissions appear to have occurred at large venues such as athletic clubs, bars, theaters and nightclubs. The majority of cases have had no documentation of complete vaccination; however, some cases were fully vaccinated.
Many of the LA County mumps cases were initially misdiagnosed, most commonly as salivary duct stones and lymphadenopathy. In addition, some misdiagnoses occurred because of reliance on false negative IgM results.
Some guidance below has been updated since the March 9, 2017 Health Alert “Mumps Clusters in Adults in Los Angeles County”.