Background: Endemic measles transmission was declared eliminated in the United States in 2000. To ensure that elimination can be maintained, high population immunity must be sustained and monitored. Testing for measles antibody was included in the National Health and Nutrition Examination Survey (NHANES), a nationally representative survey, conducted during 1999-2004.
Methods: A measles-specific immunoassay was used to measure the seroprevalence of measles antibody in NHANES participants 6-49 years of age. For analysis, participants were grouped by birth cohort.
Results: During 1999-2004, the rate of measles seropositivity in the population overall was 95.9% (95% confidence interval [CI], 95.1%-96.5%). The highest seroprevalence of measles antibody was in non-Hispanic blacks (98.6% [95% CI, 98.0%-99.1%]). Those born during 1967-1976 had significantly lower levels of measles antibody (92.4% [95% CI, 90.8%-93.9%]) than did the other birth cohorts. Independent predictors of measles seropositivity in the 1967-1976 birth cohort were non-Hispanic/black race/ethnicity, more than a high school education, having health insurance, and birth outside the United States.
Conclusions: Measles seropositivity was uniformly high in the US population during 1999-2004. Nearly all population subgroups had evidence of measles seropositivity levels greater than the estimated threshold necessary to sustain measles elimination. Non-Hispanic whites and Mexican Americans born during 1967-1976 had the lowest measles seropositivity levels and represent populations that might be at increased risk for measles disease if the virus were reintroduced into the United States.