658. Trends in Mumps Cases and Incidence, United States, January 2016‒April 2018

BACKGROUND: Since 2012, there has been a steady increase in the number of reported mumps cases and outbreaks in the United States, primarily affecting young, two-dose vaccinated adults. We analyzed epidemiologic characteristics of mumps cases reported nationally from 2016 to 2018. METHODS: We included confirmed and probable mumps cases transmitted from January 2016 to April 2018 by 52 health department jurisdictions (50 states, DC and NYC) that report cases to the National Notifiable Diseases Surveillance System (NNDSS). We calculated overall and age-specific incidence rates (IR) by dividing the annual number of mumps cases by the corresponding US Census Bureau’s Bridged Race population estimates. Cases were reported as outbreak-related or non-related in NNDSS by the submitting jurisdiction. RESULTS: Between January 1, 2016–April 21, 2018, 13,348 mumps cases (n = 6,369 in 2016, n = 6,056 in 2017 and n = 923 in 2018) were reported to NNDSS. IRs were 20, 19, and 2.9/million population in 2016, 2017, and January–April 2018, respectively. Young adults (18–22 years) had the highest IR: 88, 76, and 7.3/million population in 2016, 2017, and 2018, respectively. During January–April timeframe, 348 more cases were reported in 2016 (IR = 3.8/million) and almost four times as many cases were reported in 2017 (n = 3,376, IR = 10.5/million) compared with 2018 (P < 0.0001). The number of jurisdictions that reported cases in the first 4 months of each year was 39, 44, and 47 in 2016, 2017, and 2018, respectively. During the same timeframe, the number of outbreak-related cases reported was lower in 2018 (n = 523) vs. 2017 (n = 2,350) and 2016 (n = 1,271) (P < 0.0001), and the number of jurisdictions reporting outbreak-related cases was lower in 2018 (n = 16) vs. 2017 (n = 32, P = 0.002) and 2016 (n = 22, P = 0.23). CONCLUSION: Preliminary data suggest that the overall and outbreak-related mumps cases may be decreasing in 2018 after 2 years of increased reports. However, the number of jurisdictions reporting mumps cases has not decreased. Thorough investigations of sporadic cases may lead to improved identification of epidemiologic linkages and earlier identification of outbreaks. DISCLOSURES: All authors: No reported disclosures.