An Unusual Outbreak of Mumps in Northwest Arkansas, August-December 2016

BACKGROUND: Mumps is a viral infection spread by respiratory droplets, characterized by parotitis or inflammation of the salivary glands, and prevented by the Measles, Mumps, and Rubella (MMR) vaccine. In the past 15 years, the Arkansas Department of Health (ADH) investigated between 1 and 6 cases of mumps per year. Since August 2016, ADH has been investigating an outbreak of mumps primarily concentrated in Northwest Arkansas.

METHODS: Mumps cases are reported to ADH by healthcare providers, school nurses, and laboratories. ADH interviews all reported cases to determine exposure, travel, and vaccination history and to identify close contacts. Cases are confirmed through polymerase chain reaction (PCR) or virus isolation of buccal swabs.

RESULTS: As of January 3, 2017, ADH identified 2,416 cases associated with the outbreak, of which 1,416 were laboratory confirmed. The majority of cases are within the Marshallese (64%) who are believed to have common exposures within local churches. An estimated 6,000 to 12,000 Marshallese live in Northwest Arkansas, which is the largest population of Marshallese in the continental United States. Transmission has spread to 65 schools in 10 different school districts, 11 colleges/vocational schools, 8 private schools, 133 workplaces and 83 churches. Median age of cases is 14 years with an age range of 6 months-82 years. The majority of cases are 5-17 years old (60%). Approximately 91% of cases in children are up-to-date on vaccine. In contrast, only 46% of adult cases are up-to-date. Control measures have included offering MMR vaccines to get anyone up-to-date with the routine vaccination schedule. Offsite vaccination clinics have occurred in workplaces, churches, and housing. To date, approximately 6,737 doses of MMR have been given at 48 vaccination clinics and at our local health units. Eighteen 3^rddose MMR clinics in schools with ongoing transmission have occurred.

CONCLUSIONS: While multiple mumps outbreaks occurred across the United States in 2016, Arkansas accounted for more than half of the national cases, with a large percentage of cases being fully immunized. The challenges in Arkansas stem from the unique population of those affected. Culturally, the Marshallese are community-oriented, gathering in large settings and living in dense quarters where infections can easily spread. Language barriers as well as some vaccine hesitancy have been ongoing challenges. An evaluation of the efficacy of a 3^rd dose is currently underway through a partnership with the Centers for Disease Control and Prevention (CDC).