BACKGROUND: Mumps is an acute viral illness that classically presents with parotitis. Other presentations may include non-specific respiratory symptoms or asymptomatic infection. Mumps is transmitted by respiratory droplets and secretions, and requires close contact to spread from person-to-person. People are most contagious 2 days before until 5 days after parotitis onset; those with only non-specific respiratory symptoms or asymptomatic infections can still transmit disease. In recent years, mumps cases and incidence rates have increased, with most cases occurring among young adults (18-25 years) in close contact settings such as universities. In 2016, multiple university and close-knit community outbreaks all contributed to the high case count.
METHODS: The Centers for Disease Control and Prevention (CDC) assessed reports of confirmed and probable mumps cases transmitted from state health departments. We calculated overall and age-specific incidence rates (IR) by dividing the annual number of mumps cases by the corresponding U.S. Census Bureau’s Bridged Race population estimates.
RESULTS: From January – December 31st, 2016, 5,151 mumps cases from 47 states were reported to the Nationally Notifiable Disease Surveillance System (overall incidence rate = 16.15 per 1,000,000 persons). Two states, Arkansas and Iowa, contributed 53% of all reported cases. At least 20 states had mumps outbreaks in 2016 (defined as 3 or more cases linked by time and space); reported outbreak cases accounted for 72%. There was no difference in gender (51% male and 48% female) and most case-patients were white (52%) or Asian (41%). Of the 79% who reported vaccination status, 88% had at least one dose and 65% had two doses or more of the measles mumps rubella (MMR) vaccine. The median age was 20 years (range: <1 – 88 years). Incidence rates in all age groups increased, especially in young adults, where the IR has increased dramatically from 0.5 to 52 per 1,000,000 persons in the past five years.
CONCLUSIONS: Large outbreaks in close-contact settings contributed to the dramatic increase in the incidence of mumps in 2016. The limited spread of these outbreaks to surrounding communities emphasizes the role close contact plays in the transmission of mumps. Mumps control efforts depend on continuous infection control messaging and comprehensive, nationwide two-dose MMR coverage.