Genetic characterization of mumps viruses associated with the resurgence of mumps in the United States: 2015-2017

Despite high coverage with measles, mumps, and rubella vaccine in the United States, outbreaks of mumps occur in close contact settings such as schools, colleges, and camps. Starting in late 2015, outbreaks were reported from several universities, and by the end of 2017, greater than 13,800 cases had been reported nation-wide. In 2013, the CDC and the Association of Public Health Laboratories contracted four Vaccine Preventable Diseases Reference Centers (VPD-RCs) to perform real-time reverse transcription PCR (RT-qPCR) to detect mumps RNA in clinical samples and to determine the genotype. Twelve genotypes of mumps virus are currently recognized by the World Health Organization, and the standard protocol for genotyping requires sequencing the entire gene coding for the small hydrophobic (SH) protein. Phylogenetic analysis of the 1862 mumps samples genotyped from 2015 through 2017 showed that the overall diversity of genotypes detected was low. Only 0.8 % of the sequences were identified as genotypes C, H, J, or K, and 0.5 % were identified as vaccine strains in genotypes A or N, while most sequences (98.7 %) were genotype G. The majority of the genotype G sequences could be included into one of two large groups with identical SH sequences. Within genotype G, a small number of phylogenetically significant outlier sequences were associated with epidemiologically distinct chains of transmission. These results demonstrate that molecular and epidemiologic data can be used to track transmission pathways of mumps virus; however, the limited diversity of the SH sequences may be insufficient for resolving transmission in all outbreaks.

Mumps Outbreak in a Highly Vaccinated University-Affiliated Setting Before and After a Measles-Mumps-Rubella Vaccination Campaign-Iowa, July 2015-May 2016

Background

In response to a mumps outbreak at the University of Iowa and surrounding community, university, state, and local health officials implemented a vaccination campaign targeting students <25 years of age with an additional dose of measles-mumps-rubella (MMR) vaccine. More than 4700 vaccine campaign doses were administered; 97% were documented third doses. We describe the epidemiology of the outbreak before and after the campaign, focusing on cases in university students.

Methods

Mumps cases were identified from reportable disease databases and university health system records. Detailed information on student cases was obtained from interviews, medical chart abstractions, university and state vaccination records, and state public health laboratory results. Pre- and postcampaign incidence among students, university faculty/staff, and community members <25 vs ≥25 years old were compared using Fisher exact test. Multivariable regression modeling was performed to identify variables associated with a positive mumps polymerase chain reaction test.

Results

Of 453 cases in the county, 301 (66%) occurred in university students. Student cases were primarily undergraduates (90%) and highly vaccinated (86% had 2 MMR doses, and 12% had 3 MMR doses). Fewer cases occurred in students after the campaign (75 [25%]) than before (226 [75%]). Cases in the target group (students <25 years of age) declined 9% postcampaign (P=.01). A positive mumps polymerase chain reaction test was associated with the presence of parotitis and early sample collection, and inversely associated with recent receipt of MMR vaccine.

Conclusions

Following a large additional dose MMR vaccination campaign, fewer mumps cases occurred overall and in the target population.

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.

A Comparison of Postelimination Measles Epidemiology in the United States, 2009-2014 Versus 2001-2008

BACKGROUND

Measles, a vaccine-preventable disease that can cause severe complications, was declared eliminated from the United States in 2000. The last published summary of US measles epidemiology was during 2001-2008. We summarized US measles epidemiology during 2009-2014.

METHODS

We compared demographic, vaccination, and virologic data on confirmed measles cases reported to the Centers for Disease Control and Prevention during January 1, 2009-December 31, 2014 and January 1, 2001-December 31, 2008.

RESULTS

During 2009-2014, 1264 confirmed measles cases were reported in the United States, including 275 importations from 58 countries and 66 outbreaks. The annual median number of cases and outbreaks during this period was 130 (range, 55-667 cases) and 10 (range, 4-23 outbreaks), respectively, compared with an annual median of 56 cases (P = .08) and 4 outbreaks during 2001-2008 (P = .04). Among US-resident case-patients during 2009-2014, children aged 12-15 months had the highest measles incidence (65 cases; 8.3 cases/million person-years), and infants aged 6-11 months had the second highest incidence (86 cases; 7.3 cases/million person-years). During 2009-2014, 865 (74%) of 1173 US-resident case-patients were unvaccinated and 188 (16%) had unknown vaccination status; of 917 vaccine-eligible US-resident case-patients, 600 (65%) were reported as having philosophical or religious objections to vaccination.

CONCLUSIONS

Although the United States has maintained measles elimination since 2000, measles outbreaks continue to occur globally, resulting in imported cases and potential spread. The annual median number of cases and outbreaks more than doubled during 2009-2014 compared with the earlier postelimination years. To maintain elimination, it will be necessary to maintain high 2-dose vaccination coverage, continue case-based surveillance, and monitor the patterns and rates of vaccine exemption.