According to an investigation published in the CDC Morbidity & Mortality Weekly Report, a multistate mumps outbreak resulted from extensive social contact with an asymptomatic, fully vaccinated index patient at a wedding, resulting in a total of 62 cases.
On August 26, 2019, the Nebraska Department of Health and Human Services (DHHS) was notified by a hospital in South Dakota that 3 patients suspected of having mumps had attended a wedding in Nebraska approximately 3 weeks earlier. At the time of notification to the Nebraska DHHS, laboratory confirmation of mumps was pending. To identify further cases, an online questionnaire was developed by investigators; of the approximately 325 people who attended the wedding, 148 completed the questionnaire.
Overall, 31 secondary cases — 13 confirmed and 18 probable — were identified, 30 of whom attended the wedding and 1 who was exposed to the index patient elsewhere. Fourteen of these 31 individuals lived in the same community (labeled community A) in northeastern Nebraska. A further 27 tertiary cases were identified — 23 confirmed and 4 probable — 17 of whom resided in community A. Of the 27 tertiary cases, 6 were linked to secondary cases and 18 were linked to community events; links for the remaining 3 cases were unknown. Three quaternary cases were identified all of whom resided in community A and were linked to a tertiary case.
In total, 62 cases were identified, 54 of whom were Nebraska residents and 8 resided in other states. Non-Nebraska cases included 3 secondary cases among wedding attendees from South Dakota, 1 tertiary case from South Dakota, and 4 secondary cases, one each from Idaho, Minnesota, North Dakota, and Wyoming. Median patient age was 35 years (range, 6-59) and all were old enough to have received 2 doses of measles, mumps, and rubella (MMR) vaccination; 41 individuals reported receiving ≥2 doses of MMR. No serious complications or hospitalizations associated with mumps were reported.
According to the investigators, “asymptomatic transmission of mumps in a conducive environment is capable of producing a widespread outbreak.” The isolation of ill people and a community-wide MMR vaccination campaign helped to end the outbreak. As of December 1, 2019, no additional cases were reported. The investigators also noted that “collaborative efforts, including early and regular communication between local, state, and national public health authorities, local health care providers, and community officials proved crucial for efficient resource mobilization, strengthened preparedness, and resulted in effective disease containment.”
Donahue M, Hendrickson B, Julian D, et al. Multistate mumps outbreak originating from asymptomatic transmission at a Nebraska wedding – six states, August-October 2019. MMWR Morb Mortal Wkly Rep. 2020;69(22):666-669.