Epidemiology of SARS-CoV-2 transmission and superspreading in Salt Lake County, Utah, March-May 2020

BACKGROUND

Understanding the drivers of SARS-CoV-2 transmission can inform the development of interventions. We evaluated transmission identified by contact tracing investigations between March-May 2020 in Salt Lake County, Utah, to quantify the impact of this intervention and identify risk factors for transmission.

METHODS

RT-PCR positive and untested symptomatic contacts were classified as confirmed and probable secondary case-patients, respectively. We compared the number of case-patients and close contacts generated by different groups, and used logistic regression to evaluate factors associated with transmission.

RESULTS

Data were collected on 184 index case-patients and up to six generations of contacts. Of 1,499 close contacts, 374 (25%) were classified as secondary case-patients. Decreased transmission odds were observed for contacts aged <18 years (OR = 0.55 [95% CI: 0.38-0.79]), versus 18-44 years, and for workplace (OR = 0.36 [95% CI: 0.23-0.55]) and social (OR = 0.44 [95% CI: 0.28-0.66]) contacts, versus household contacts. Higher transmission odds were observed for case-patient's spouses than other household contacts (OR = 2.25 [95% CI: 1.52-3.35]). Compared to index case-patients identified in the community, secondary case-patients identified through contract-tracing generated significantly fewer close contacts and secondary case-patients of their own. Transmission was heterogeneous, with 41% of index case-patients generating 81% of directly-linked secondary case-patients.

CONCLUSIONS

Given sufficient resources and complementary public health measures, contact tracing can contain known chains of SARS-CoV-2 transmission. Transmission is associated with age and exposure setting, and can be highly variable, with a few infections generating a disproportionately high share of onward transmission.

LB16. The Role of Adults in the Measles Outbreak in New York State Outside of New York City, 2018–2019

Background

The United States is experiencing the largest measles outbreak since elimination was declared in 2000, with the majority of cases in NYS reported in undervaccinated communities. The objective of this evaluation was to describe adult measles cases in the NYS measles outbreak outside of New York City (NYC).

Methods

We included all confirmed cases aged ≥18 years in NYS residents (excluding NYC) during October 1, 2018–July 25, 2019 that met the CSTE measles case definition. We defined measles cases attributable to adults as the sum of measles cases among adults and children who contracted disease directly from adults.

Results

Among 371 confirmed measles cases, the median age was 5.5 years (range: 1 day to 64 years); 79 (21%) were in adults, 4 (5%) of whom were born before 1957 (3 unvaccinated and 1 with unknown vaccine status). Among the 75 cases born during or after 1957, 65 (87%) were unvaccinated or had unknown vaccine status, while 3 had one dose and 7 had 2 doses of measles vaccine. Notably, 5 of 11 internationally imported measles cases were adults, and all were unvaccinated or had unknown vaccine status. During the first month of the outbreak, 26 of the 51 (51%) cases were attributable to adults; of the 26, 15 (58%) were in adults and 11 (42%) were in children who acquired infection from adults (Figure 3).

Conclusion

The majority of measles cases occurred in unvaccinated children emphasizing the importance of ongoing and focused efforts on pediatric vaccination. However, measles cases in unvaccinated adults played an important role in both importations and disease transmission early in the outbreak. These data strongly support current recommendations of 1 dose of measles, mumps, rubella vaccine (MMR) for most adults and 2 doses of MMR for adults traveling internationally and at high-risk such as those in outbreak areas, as determined by local/state public health.

Disclosures

Kirsten St. George, MAppSc, PhD, Akonni Biosystems (Other Financial or Material Support), ThermoFisher (Grant/Research Support), Zeptometrix (Other Financial or Material Support, royalty generating collaborative agreement). .

2769. The Clinical and Economic Impact of MMR Vaccinations to Prevent Measles Importations from US Pediatric Travelers Returning from Abroad

Background

Although pediatric travelers comprise < 10% of US international travelers, they account for almost half of all measles importations among returning travelers. For travelers 1–18 years with no other evidence of measles immunity, the Advisory Committee on Immunization Practices (ACIP) recommends 2 MMR vaccine doses before departure; 1 dose is recommended for infant travelers (6 to <12 months) and does not count toward their primary immunization series. All US travelers (6 months to < 6 years) are at risk for being undervaccinated for measles because MMR is routinely given at 1 years and 4–6 years.

Methods

We developed a decision tree model to evaluate the clinical impact and cost per case averted of pretravel health encounters (PHE) that vaccinate MMR-eligible pediatric international travelers. We compared 2 strategies for infant (6 to < 12 months) and preschool-aged (1 to <6 years) travelers: (1) no PHE: travelers departed with baseline MMR vaccination status vs. (2) PHE: MMR-eligible travelers were offered vaccination. All simulated travelers experienced a destination-specific risk of measles exposure during travel (mean, 237exposures/10M travelers; range, 19–6,750 exposures/10M travelers); if exposed to measles, travelers were at risk of illness stratified by age and MMR vaccination status (range, 0.03–0.90). Costs include direct medical costs and lost work wages for guardians. Model outcomes included measles cases, costs, and cost per case averted. We varied inputs in sensitivity analyses.

Results

Compared with no PHE, PHE averted 451 measles cases at $985,000/case averted for infant travelers and 54 measles cases at $1.5 million/case averted for preschool-aged travelers (table, bottom). PHE can be cost-saving for travelers to regions with higher risk of measles exposure and if more MMR-eligible travelers are vaccinated at PHE (Figure 1). At a risk of exposure associated with European travel, PHE had better value when a measles importation led to a higher number of contacts or more US-acquired cases per importation (Figure 2).

Conclusion

PHE for pediatric travelers (6 months to <6 years) decreased the number of imported measles cases and saved costs, especially if targeted to travelers with higher-risk destinations, if more MMR-eligible travelers are vaccinated at PHE, or if outbreaks are larger.

Disclosures

All authors: No reported disclosures.

LB15. Measles Outbreak in New York State (NYS) Outside of New York City, 2018–2019

Background

The United States is experiencing one of the largest and longest measles outbreaks since elimination was declared in 2000 and is at risk of losing this status. Most cases occurring in NYS were reported in undervaccinated communities.

Methods

We included all confirmed NYS measles cases (excluding NYC) from outbreak counties from October 1, 2018 to July 25, 2019. We used the CSTE measles case definition requiring an acute febrile rash illness and either laboratory confirmation or direct epidemiologic linkage to a lab-confirmed case. For each case, demographic and clinical characteristics were obtained. A medical record review was completed for those reported to have an encounter at a hospital, emergency department, or urgent care center.

Results

There were 371 cases of measles reported, including 11 internationally imported cases. Most occurred in Rockland county (n = 283); followed by Orange (n = 55), Westchester (n = 18), Sullivan (n = 14) and Greene (n = 1) (Figures 1 and 2). The median age was 5.5 years; 79% of all cases occurred among children younger than 18 years of age (Figure 3). Most cases (79%) had not received any doses of measles vaccine. Of the 371 cases, 263 (71%) were children who had received 0 doses of measles, mumps, rubella vaccine (MMR), 218 (83%) of whom were over 1 year of age (Table 1). There have been no deaths or documented cases of encephalitis. Twenty-eight (8%) patients were diagnosed with pneumonia and 25 (7%) patients were hospitalized. Among 17 hospitalized children, 5 (29%) were admitted to the intensive care unit (ICU) (ages 1 day to 7 years). There were two preterm births at 34 and 25 weeks gestation to women with measles while pregnant. During October 1, 2018–July 31, 2019, providers in outbreak counties vaccinated 72,465 individuals with MMR, a 46% increase from the same period the year prior.

Conclusion

Unvaccinated children were identified as the largest group affected and experienced severe complications; nearly 30% of hospitalized children were admitted to an ICU. These data support the critical need for continued education and outreach on the risks of measles and the value of vaccination to prevent continued circulation in undervaccinated communities and potential further cases of severe disease.

Disclosures

Kirsten St. George, MAppSc, PhD, Akonni Biosystems (Other Financial or Material Support), ThermoFisher (Grant/Research Support), Zeptometrix (Other Financial or Material Support, royalty generating collaborative agreement); others, no disclosures reported..

2901. Measles in the United States During the Postelimination Era, 2017–2019

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.

660. Are US Clinicians Thinking Measles in the Post-elimination Era? Surveillance for Measles-Like Illness in a Commercially Insured US Population

Background

In September 2016, the Americas was the first region to eliminate measles, a highly contagious, vaccine-preventable disease that can lead to complications and death. To maintain elimination, the Pan American Health Organization (PAHO) suggested a minimum rate of suspected measles investigations (≥2 per 100,000 population) be conducted annually. However, measles-like illness (MLI) investigations conducted by US clinicians are not tracked by the measles surveillance program in the United States. To ensure the US meets PAHO standards, we estimated the rate of MLI investigations using a large insurance claims database.

Methods

We used the 2009–2016 Truven Health MarketScan^® Databases to identify MLI and MLI investigations. MLI were defined using International Classification of Diseases (ICD)-9/10 diagnostic codes in two ways: a priori, using the Council of State and Territorial Epidemiologists (CSTE) measles case definition or empirically, using ICD codes on insurance claims with a measles diagnostic code. MLI investigations were defined as MLI occurring up to 5 days prior to a measles diagnostic code or billing code for measles serology testing. We computed annual rates of MLI investigations per 100,000 population.

Results

We identified ~35.5 million MLI using the a priori definition. Of these, 24,010 had a measles serology code within 5 days; median age was 30 and 51% were aged 18–34 years. Using the empirical definition we identified ~46 million MLI. Of these, 29,940 were coupled with a measles serology code; median age was 31 and 50% were aged 18–34 years. The median annual rates for MLI investigations were 3.2 (a priori) and 4.3 (empirical) per 100,000 population.

Conclusion

Maintaining measles elimination requires continued vigilance by clinicians and high-quality case-based surveillance. The estimated rates of MLI investigations in this US population exceeded the PAHO standard, suggesting that the quality of US measles surveillance is robust.

Disclosures

All authors: No reported disclosures.