BACKGROUND: Since 2006, mumps cases and outbreaks have been increasingly associated with university students and college campuses. Most cases are occurring in students who have completed the two-dose measles-mumps-rubella (MMR) vaccine series appropriately. Further understanding of exposures and risk factors for mumps infection in this population is needed to identify potential target areas for messaging and intervention.
METHODS: Data were collected on students who attended two outbreak vaccination clinics and those who were cases during an outbreak of mumps at a small, private university in Indiana in 2016. Clinic attendees who were not known outbreak cases were surveyed about known exposures (defined as direct contact with or notification of exposure from a confirmed or probable case), living conditions, extracurricular activities, and vaccination status. Data for mumps cases was abstracted from investigations in the Indiana National Electronic Disease Surveillance System. Associations were analyzed using chi-square and Fisher’s exact tests, and measured using odds ratios.
RESULTS: Completed survey information or case data was collected for 1,427 individuals. Of these, 25 (1.8%) individuals were identified as confirmed or probable cases of mumps. Responders were aged from 17 years to 66 years (mean: 23 years; median: 20 years). A history of two or more doses of mumps-containing vaccine was self-reported by 1100 (77.1%) individuals. Thirty (2.1%) respondents reported mumps infection during childhood. Of 1,427 individuals studied, 48.9% reported sorority or fraternity affiliation, 22.0% reported dormitory residence, 23.0% reported participation in an athletic team or group, and 29.9% reported participation in another club or group. Known exposure to a confirmed or probable case was significantly associated with becoming a mumps case (OR: 28.8; 95%CI: 11.8-70.3) as was sorority or fraternity affiliation (OR: 2.7; 95% CI: 1.1-6.6). One particular fraternity was identified as a possible source by 56% of cases, independent of membership in that organization. Participation in college athletics, number of MMR vaccine doses, residence in a dormitory, and other club participation were not significantly associated with developing mumps in this population.
CONCLUSIONS: This university outbreak occurred in a highly vaccinated population. Sorority or fraternity affiliation was significantly associated with developing mumps in this outbreak, however, much of this association may be accounted for by the large involvement of one fraternity. These results indicate a continued need to focus on control measure strengthening and enforcement for known contacts of cases and groups for whom risk is high in collegiate mumps outbreaks.