Mumps, 2016: A National Overview

BACKGROUND: Mumps is an acute viral illness that classically presents with parotitis. Infected persons who are asymptomatic or have non-specific respiratory symptoms can still transmit disease. Recently, mumps cases and outbreaks (OB) among young adults (18-22 years) in the US have been increasing. In 2016, university and close-knit community OB accounted for the highest incidence rates (IR) since 2006 (Figure 1). METHODS: The Centers for Disease Control and Prevention (CDC) assessed reports of confirmed and probable mumps cases transmitted through passive surveillance by 52 state/local health departments (jurisdictions). Nine jurisdictions submitted enhanced OB data including symptoms and complications directly to CDC. We calculated overall and age-specific IR (per 1,000,000 persons, 95% CI) by dividing the annual number of mumps cases by U.S. Census Bureau’s population estimates. SAS (v9.4) was used for analysis. RESULTS: From January–December 31, 2016, 5,724 mumps cases from 48 jurisdictions were reported (overall IR: 18). Of 79% with vaccination status, 88% had ≥1 dose and 60% had ≥2 doses of measles mumps rubella (MMR) vaccine. Median age was 20 years (range: <1–88 years). Incidence rates significantly increased for all age groups from 2011 to 2016 (1.2 (CI: 1.2–1.4) to 18 (17–18), P < 0.0001). IR in young adults increased from 4.1 (CI: 3.3–5.0) to 70 (CI: 66–73), P < .0001 (Figure 2). Twenty-nine jurisdictions reported mumps OB (defined as ≥3 cases linked by time/space); OB accounted for ~81% of all cases. Two states, Arkansas and Iowa, contributed 53% of all cases. Among jurisdictions with enhanced OB data, 20 OB (median 12 cases, range: 3–685) with a total of 1379 outbreak cases were reported. Parotitis was reported in 99% of cases. Complications were low: orchitis was reported in 7% of males and oophoritis in 2% of females; ≤1% reported hearing loss, mastitis, encephalitis or pancreatitis. Average report time from symptom onset to health department was 6 days. Ten OB had population vaccination coverage ≥85%. CONCLUSION: OB contributed to a significant increase in mumps incidence in 2016. Although most cases occurred in young adults vaccinated with 2 doses during childhood thus suggesting waning immunity, complications remain rare. DISCLOSURES: All authors: No reported disclosures.