Can a minimum rate of investigation of measleslike illnesses serve as a standard for evaluating measles surveillance?

To determine whether measles case finding is sensitive, we developed a standard by which to evaluate measles surveillance. We compiled data on the incidence of measleslike illnesses (MLIs) from multiple, diverse sources and used the distribution of these values to determine the minimum level of measles case-finding activity that could be expected in a given region. Among surveillance programs in the United States, other countries in the Americas, and other World Health Organization regions, the median annual rates for rash investigations that were ruled out for measles were 4.3, 4.1, and 1.8/100,000 population, respectively. The annual rates of measles IgM testing in the United States in public laboratories and commercial laboratories were 1.6 and 9.2/100,000 population, respectively. In total, we collected data on annual MLI incidence from 180 sources. Values ranged from 0.1 to 22.6 cases of MLI per 100,000 population, and 90% of values were greater than or equal to1.0/100,000 population. On the basis of these findings, we propose that programs attempting measles elimination consider evaluating surveillance by comparing the annual rate of suspected measles investigations against a minimum standard of 1/100,000 population.