Althoughmeasles elimination has been maintained in the United States for the past 20 years, emerging trends of increased transmission related to clustering of unvaccinated persons highlight the need to close existing immunity gaps and the importance of outbreak preparedness. Background Measles elimination (interruption of endemic measles virus transmission) in the United States was declared in 2000; however, the number of cases and outbreaks have increased in recent years. We characterized the epidemiology of measles outbreaks and measles transmission patterns after elimination to identify potential gaps in the US measles control program. Methods We analyzed national measles notification data from 1 January 2001 to 31 December 2019. We defined measles infection clusters as single cases (isolated cases not linked to additional cases), 2-case clusters, or outbreaks with >= 3 linked cases. We calculated the effective reproduction number (R) to assess changes in transmissibility and reviewed molecular epidemiology data. Results During 2001-2019, a total of 3873 measles cases, including 747 international importations, were reported in the United States; 29% of importations were associated with outbreaks. Among 871 clusters, 69% were single cases and 72% had no spread. Larger and longer clusters were reported since 2013, including 7 outbreaks with >50 cases lasting >2 months, 5 of which occurred in known underimmunized, close-knit communities. No measles lineage circulated in a single transmission chain for >12 months. Higher estimates of R were noted in recent years, although R remained below the epidemic threshold of 1. Conclusions Current epidemiology continues to support the interruption of endemic measles virus transmission in the United States. However, larger and longer outbreaks in recent postelimination years and emerging trends of increased transmission in underimmunized communities emphasize the need for targeted approaches to close existing immunity gaps and maintain measles elimination.

During January 1-October 1, 2019, a total of 1,249 measles cases and 22 measles outbreaks were reported in the United States. This represents the most U.S. cases reported in a single year since 1992 (1), and the second highest number of reported outbreaks annually since measles was declared eliminated* in the United States in 2000 (2). Measles is an acute febrile rash illness with an attack rate of approximately 90% in susceptible household contacts (3). Domestic outbreaks can occur when travelers contract measles outside the United States and subsequently transmit infection to unvaccinated persons they expose in the United States. Among the 1,249 measles cases reported in 2019, 1,163 (93%) were associated with the 22 outbreaks, 1,107 (89%) were in patients who were unvaccinated or had an unknown vaccination status, and 119 (10%) measles patients were hospitalized. Closely related outbreaks in New York City (NYC) and New York State (NYS; excluding NYC), with ongoing transmission for nearly 1 year in large and close-knit Orthodox Jewish communities, accounted for 934 (75%) cases during 2019 and threatened the elimination status of measles in the United States. Robust responses in NYC and NYS were effective in controlling transmission before the 1-year mark; however, continued vigilance for additional cases within these communities is essential to determine whether elimination has been sustained. Collaboration between public health authorities and undervaccinated communities is important for preventing outbreaks and limiting transmission. The combination of maintenance of high national vaccination coverage with measles, mumps, and rubella vaccine (MMR) and rapid implementation of measles control measures remains the cornerstone for preventing widespread measles transmission (4).

As of April 26, 2019, CDC had reported 704 cases of measles in the United States since the beginning of 2019, representing the largest number of cases reported in the country in a single year since 1994, when 963 cases occurred, and since measles was declared eliminated* in 2000 (1,2). Measles is a highly contagious, acute viral illness characterized by fever and a maculopapular rash; complications include pneumonia, encephalitis, and death. Among the 704 cases, 503 (71%) were in unvaccinated persons and 689 (98%) occurred in U.S. residents. Overall, 66 (9%) patients were hospitalized. Thirteen outbreaks have been reported in 2019, accounting for 663 cases, 94% of all reported cases. Six of the 13 outbreaks were associated with underimmunized close-knit communities and accounted for 88% of all cases. High 2-dose measles vaccination coverage in the United States has been critical to limiting transmission (3). However, increased global measles activity poses a risk to U.S. elimination, particularly when unvaccinated travelers acquire measles abroad and return to communities with low vaccination rates (4). Health care providers should ensure persons are up to date with measles, mumps, rubella (MMR) vaccine, including before international travel, and rapidly report all suspected cases of measles to public health authorities.

Abstract Background Measles, a vaccine-preventable viral illness that can cause serious complications, was declared eliminated from the United States in 2000 because of a successful measles vaccination program. Recent years have seen an increase in the number of measles cases and outbreaks. We summarized measles epidemiology in the United States during 2017–2019. Methods We reviewed US national surveillance data on confirmed measles cases reported to the Centers for Disease Control and Prevention during January 1, 2017–April 26, 2019. We describe the demographic characteristics, vaccination status, and disease epidemiology of measles cases. Results During 2017–April 2019, 1,196 measles cases were reported in 37 US States and Washington DC, including 146 (12%) importations from 37 countries; 108 (74%) of importations were US residents returning from travel abroad, of which 60 (56%) were unvaccinated and 31 (29%) had unknown vaccinations status. Among 1,148 cases who were US-residents, the highest incidence of measles was among infants and children aged 6–11 and 12–15 months (112 cases [19 cases/million person-years] and 106 cases [27 cases/million person-years], respectively). Among US-resident cases, 846 (74%) were unvaccinated and 163 (14%) had unknown vaccination status; 777 (68%) were considered to have preventable measles (i.e., were eligible for vaccination but unvaccinated). Among the 1,196 cases, 85 were single cases, and the remaining 1,111 represented 19 two-case chains and 34 outbreaks of 3 or more cases linked epidemiologically; the median outbreak size and duration was 6 cases (range, 3 to 452 cases) and 19.5 days (range, 5 to 205 days). A total of 934 (78%) of the 1196 cases and 13 (38%) of the 34 outbreaks occurred in under-immunized close-knit communities; eight outbreaks are ongoing. Conclusion Outbreaks of measles in the United States result from recurring measles introductions and subsequent measles spread, especially in under-immunized close-knit communities. To sustain measles elimination, it will be necessary to maintain timely routine high coverage with MMR vaccine, improve implementation of pretravel recommendations to minimize importations, and close immunity gaps in communities of US residents who remain unvaccinated. Disclosures All Authors: No reported Disclosures.

Background Mumps is an acute viral illness that classically presents with parotitis. Although the United States experienced a 99% reduction in mumps cases following implementation of the 2-dose vaccination program in 1989, mumps has resurged in the past 10 years. Methods We assessed the epidemiological characteristics of mumps outbreaks with ≥20 cases reported in the United States electronically through the National Notifiable Diseases Surveillance System and from supplemental outbreak data through direct communications with jurisdictions from July 2010 through December 2015. Mumps cases were defined using the 2012 Council of State and Territorial Epidemiologists case definition. Results Twenty-three outbreaks with 20-485 cases/outbreak were reported in 18 jurisdictions. The duration of outbreaks ranged from 1.5-8.5 months (median: 3 months). All outbreaks involved close-contact settings; 18 (78%) involved universities, 16 (70%) occurred primarily among young adults (median: 18-24 years of age), and 9 (39%) occurred in highly vaccinated populations (2 dose measles-mumps-rubella [MMR] vaccine coverage >85%). Conclusions During 2010-2015, multiple mumps outbreaks among highly vaccinated populations in close-contact settings occurred. Most cases occurred among vaccinated young adults, suggesting waning immunity played a role. Further evaluation of risk factors associated with these outbreaks is warranted.

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). 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. 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%. 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. All authors: No reported disclosures.

Measles is a highly contagious vaccine-preventable disease that can lead to serious complications. Although measles was declared eliminated from the United States in 2000, measles cases and outbreaks continue to occur each year as a result of importations of the disease from countries in which it remains endemic. We describe the epidemiology of importations of measles virus into the US during the post-elimination era. Measles is nationally notifiable in the USA and local and state health departments report confirmed measles cases to the Centers for Disease Control and Prevention (CDC). A case is considered internationally imported if at least some of the exposure period (7-21 days before rash onset) occurred outside of the USA, rash onset occurred within 21 days of entering the USA, and there was no known exposure to measles in the US during that time. We describe the demographic characteristics, source regions, and vaccination status of measles importations during 2001–2015. From 2001 to 2015, 2,012 measles cases were reported to CDC; 535 (27%) were imported. A median of 28 importations occurred each year (range: 18–80). The median age of imported cases was 18 years (range: <1–75 years), 50% were male, 87% were unvaccinated or had unknown vaccination status, and 63% reported travel to countries in the Western Pacific and European Regions of the World Health Organization during their exposure periods. Half of all imported cases had rash onset between January and April. Overall, 62% (n = 332) of importations occurred among US residents, varying from a low of 37% in 2001 to a high of 89% in 2014. One imported case occurred among a US resident too young to be vaccinated, and 15 (5%) occurred among US residents born before 1957 (presumed immune from natural disease), and thus were not vaccine preventable. Importations of measles virus will continue to occur as long as measles remains endemic in many parts of the world. In the post-elimination era in the US, the majority of importations were among US residents, almost all of which were vaccine preventable. Our findings emphasize the importance of measles vaccination of individuals aged ≥6 months prior to international travel, per ACIP recommendations, and of supporting global measles control efforts. All authors: No reported disclosures.

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.

We assessed the status of measles elimination in the United States using outbreak notification data. Measles transmissibility was assessed by estimation of the reproduction number, R, the average number of secondary cases per infection, using 4 methods; elimination requires maintaining R at <1. Method 1 estimates R as 1 minus the proportion of cases that are imported. Methods 2 and 3 estimate R by fitting a model of the spread of infection to data on the sizes and generations of chains of transmission, respectively. Method 4 assesses transmissibility before public health interventions, by estimating R for the case with the earliest symptom onset in each cluster (Rindex). During 2001-2014, R and Rindex estimates obtained using methods 1-4 were 0.72 (95% confidence interval (CI): 0.68, 0.76), 0.66 (95% CI: 0.62, 0.70), 0.45 (95% CI: 0.40, 0.49), and 0.63 (95% CI: 0.57, 0.69), respectively. Year-to-year variability in the values of R and Rindex and an increase in transmissibility in recent years were noted with all methods. Elimination of endemic measles transmission is maintained in the United States. A suggested increase in measles transmissibility since elimination warrants continued monitoring and emphasizes the importance of high measles vaccination coverage throughout the population.

BACKGROUND:Although measles was eliminated in the United States in 2000, importations of the virus continue to cause outbreaks. We describe the epidemiologic features of an outbreak of measles that originated from two unvaccinated Amish men in whom measles was incubating at the time of their return to the United States from the Philippines and explore the effect of public health responses on limiting the spread of measles.METHODS:We performed descriptive analyses of data on demographic characteristics, clinical and laboratory evaluations, and vaccination coverage.RESULTS:From March 24, 2014, through July 23, 2014, a total of 383 outbreak-related cases of measles were reported in nine counties in Ohio. The median age of case patients was 15 years (range, <1 to 53); a total of 178 of the case patients (46%) were female, and 340 (89%) were unvaccinated. Transmission took place primarily within households (68% of cases). The virus strain was genotype D9, which was circulating in the Philippines at the time of the reporting period. Measles-mumps-rubella (MMR) vaccination coverage with at least a single dose was estimated to be 14% in affected Amish households and more than 88% in the general (non-Amish) Ohio community. Containment efforts included isolation of case patients, quarantine of susceptible persons, and administration of the MMR vaccine to more than 10,000 persons. The spread of measles was limited almost exclusively to the Amish community (accounting for 99% of case patients) and affected only approximately 1% of the estimated 32,630 Amish persons in the settlement.CONCLUSIONS:The key epidemiologic features of a measles outbreak in the Amish community in Ohio were transmission primarily within households, the small proportion of Amish people affected, and the large number of people in the Amish community who sought vaccination. As a result of targeted containment efforts, and high baseline coverage in the general community, there was limited spread beyond the Amish community. (Funded by the Ohio Department of Health and the Centers for Disease Control and Prevention.).

ABSTRACT In the United States, approximately 9% of the measles cases reported from 2012 to 2014 occurred in vaccinated individuals. Laboratory confirmation of measles in vaccinated individuals is challenging since IgM assays can give inconclusive results. Although a positive reverse transcription (RT)-PCR assay result from an appropriately timed specimen can provide confirmation, negative results may not rule out a highly suspicious case. Detection of high-avidity measles IgG in serum samples provides laboratory evidence of a past immunologic response to measles from natural infection or immunization. High concentrations of measles neutralizing antibody have been observed by plaque reduction neutralization (PRN) assays among confirmed measles cases with high-avidity IgG, referred to here as reinfection cases (RICs). In this study, we evaluated the utility of measuring levels of measles neutralizing antibody to distinguish RICs from noncases by receiver operating characteristic curve analysis. Single and paired serum samples with high-avidity measles IgG from suspected measles cases submitted to the CDC for routine surveillance were used for the analysis. The RICs were confirmed by a 4-fold rise in PRN titer or by RT-quantitative PCR (RT-qPCR) assay, while the noncases were negative by both assays. Discrimination accuracy was high with serum samples collected ≥3 days after rash onset (area under the curve, 0.953; 95% confidence interval [CI], 0.854 to 0.993). Measles neutralizing antibody concentrations of ≥40,000 mIU/ml identified RICs with 90% sensitivity (95% CI, 74 to 98%) and 100% specificity (95% CI, 82 to 100%). Therefore, when serological or RT-qPCR results are unavailable or inconclusive, suspected measles cases with high-avidity measles IgG can be confirmed as RICs by measles neutralizing antibody concentrations of ≥40,000 mIU/ml.

Between 2001 and 2014, 78 reported measles cases resulted from transmission in US healthcare facilities, and 29 healthcare personnel were infected from occupational exposure, 1 of whom transmitted measles to a patient. The economic impact of preventing and controlling measles transmission in healthcare facilities was $19 000-$11 4286 per case.

Measles is a highly contagious, acute viral illness that can lead to complications such as pneumonia, encephalitis, and death. As a result of high 2-dose measles vaccination coverage in the United States and improved control of measles in the World Health Organization's Region of the Americas, the United States declared measles elimination (defined as interruption of year-round endemic transmission) in 2000. Importations from other countries where measles remains endemic continue to occur, however, which can lead to clusters of measles cases in the United States. To update surveillance data on current measles outbreaks, CDC analyzed cases reported during January 4-April 2, 2015. A total of 159 cases were reported during this period. Over 80% of the cases occurred among persons who were unvaccinated or had unknown vaccination status. Four outbreaks have occurred, with one accounting for 70% of all measles cases this year. The continued risk for importation of measles into the United States and occurrence of measles cases and outbreaks in communities with high proportions of unvaccinated persons highlight the need for sustained, high vaccination coverage across the country.

Measles is a highly contagious, acute viral illness that can lead to serious complications and death. Although measles elimination (i.e., interruption of year-round endemic transmission) was declared in the United States in 2000, importations of measles cases from endemic areas of the world continue to occur, leading to secondary measles cases and outbreaks in the United States, primarily among unvaccinated persons. To update national measles data in the United States, CDC evaluated cases reported by states from January 1 through May 23, 2014. A total of 288 confirmed measles cases have been reported to CDC, surpassing the highest reported yearly total of measles cases since elimination (220 cases reported in 2011). Fifteen outbreaks accounted for 79% of cases reported, including the largest outbreak reported in the United States since elimination (138 cases and ongoing). The large number of cases this year emphasizes the need for health-care providers to have a heightened awareness of the potential for measles in their communities and the importance of vaccination to prevent measles.

Background. Although measles was declared eliminated in the U.S. in 2,000, importations from remaining endemic areas in the world continue to occur, and lead to outbreaks in pockets of unvaccinated. Due to an apparent increase in the number of cases and outbreaks in recent years, and concerns of increasing vaccine hesitancy, we evaluated transmission from imported cases to assess measles elimination status in the U.S. Methods. Measles elimination was assessed by evaluation of the effective reproduction number R, the average number of secondary cases that result from an importation; elimination is indicated by maintenance of R < 1. Four previously described methods for estimating R were applied to national surveillance data reported to the CDC from 2001-2013. Method 1 estimates R as 1-P, where P is the proportion of all cases that are imported. Methods 2 and 3 estimate R by fitting a model of the spread of infection, based on a branching process, to data on the observed sizes and generations of outbreaks, respectively. An outbreak was defined as 1 or more cases. Method 4 estimates R from the observed epidemic curves of the largest outbreaks, using a likelihood-based estimation approach. Inverse-variance-weighting was applied to yearspecific R estimates to analyze trends overtime. Results. During 2001-2013, a total of 1153 confirmed measles cases were reported, of which 447 were importations. These constituted 525 outbreaks, ranging in size from 1 to 58 cases; 145 had >1 case. Median outbreak duration was 15 days (range 1-89 days). Across all study years, R was <1 with all 4 methods: 0.62 (95% CI: 0.54-0.72) using method 1, 0.52 (95% CI: 0.39-0.64) using method 2, 0.66 (95% CI: 0.62-0.71) using method 3, and 0.63 (95% CI: 0.60-0.66) using method 4. A statistically significant trend in annual R estimates overtime was not identified (p-value > 0.2). Conclusion. Our estimates of R demonstrate that elimination of endemic measles transmission is maintained in the U.S. The congruence in results using different methods augments the validity of the estimates and provides a framework for continued monitoring of elimination. Sustained high vaccination coverage and prompt outbreak response strategies have proven successful in halting prolonged transmission of measles in the U.S. Disclosures. All authors: No reported disclosures.

Background: Flight-related measles contact investigations in the United States are coordinated by the Centers for Disease Control and Prevention (CDC). To evaluate the efficiency of CDC's measles protocol, we analyzed data from contact investigations conducted December 2008-December 2011.Methods: Cases were defined as travelers diagnosed with measles that were infectious at the time of the flight. Passengers seated within 2 rows of the case-traveler and all babies-in-arms were defined as contacts. Contact information obtained from airlines was distributed to US health departments; reporting of outcomes was requested. We cross-referenced the National Notifiable Diseases Surveillance System and CDC's National Center for Immunization and Respiratory Diseases to identify unreported cases in passenger-contacts and in passengers not identified as contacts.Results: Our evaluation included 74 case-travelers on 108 flights. Information for 2673 (79%) of 3399 passenger-contacts was provided to health departments; 9 cases of secondary measles were reported. No additional cases were identified.Conclusion: Our evaluation provided evidence of measles transmission related to air travel. CDC's protocol efficiently identifies passengers most at risk of exposure and infection for flights into and within the United States. Published by Elsevier Ltd.

IMPORTANCETo verify the elimination of endemic measles, rubella, and congenital rubella syndrome (CRS) from the Western hemisphere, the Pan American Health Organization requested each member country to compile a national elimination report. The United States documented the elimination of endemic measles in 2000 and of endemic rubella and CRS in 2004. In December 2011, the Centers for Disease Control and Prevention convened an external expert panel to review the evidence and determine whether elimination of endemic measles, rubella, and CRS had been sustained.OBJECTIVETo review the evidence for sustained elimination of endemic measles, rubella, and CRS from the United States through 2011.DESIGN, SETTING, AND PARTICIPANTSReview of data for measles from 2001 to 2011 and for rubella and CRS from 2004 to 2011 covering the US resident population and international visitors, including disease epidemiology, importation status of cases, molecular epidemiology, adequacy of surveillance, and population immunity as estimated by national vaccination coverage and serologic surveys.MAIN OUTCOMES AND MEASURESAnnual numbers of measles, rubella, and CRS cases, by importation status, outbreak size, and distribution; proportions of US population seropositive for measles and rubella; and measles-mumps-rubella vaccination coverage levels.RESULTSSince 2001, US reported measles incidence has remained below 1 case per 1,000,000 population. Since 2004, rubella incidence has been below 1 case per 10,000,000 population, and CRS incidence has been below 1 case per 5,000,000 births. Eighty-eight percent of measles cases and 54% of rubella cases were internationally imported or epidemiologically or virologically linked to importation. The few cases not linked to importation were insufficient to represent endemic transmission. Molecular epidemiology indicated no endemic genotypes. The US surveillance system is adequate to detect endemic measles or rubella. Seroprevalence and vaccination coverage data indicate high levels of population immunity to measles and rubella.CONCLUSIONS AND RELEVANCEThe external expert panel concluded that the elimination of endemic measles, rubella, and CRS from the United States was sustained through 2011. However, international importation continues, and health care providers should suspect measles or rubella in patients with febrile rash illness, especially when associated with international travel or international visitors, and should report suspected cases to the local health department.