Assessment of declines in reported tuberculosis cases--Georgia and Pennsylvania, 2009.

In 2009, the largest single-year percentage decrease in tuberculosis (TB) cases was reported since national TB surveillance began in the United States in 1953. Overall, TB rates decreased 11.4% to 3.8 cases per 100,000 population, compared with an average annual decline of 3.8% each year since 2000. Georgia and Pennsylvania were among 36 states reporting decreases from 2008; TB case rates fell 14.3% (from 4.9 to 4.2) in Georgia and 38.7% (from 3.1 to 1.9) in Pennsylvania. Concerned about the possibility of unidentified TB cases, the Georgia Division of Public Health and the Pennsylvania Department of Health, in collaboration with CDC, conducted investigations centering on four hypotheses for the declines: 1) surveillance artifact, 2) underreporting, 3) underdiagnosis, and 4) actual decline. This report summarizes the results of those investigations, which found no evidence of surveillance artifact, underreporting, or underdiagnosis substantial enough to account for the magnitude of the declines. Instead, a decrease in the number of laboratory-confirmed Mycobacterium tuberculosis complex diagnoses and a decrease in the percentage of suspected TB cases ultimately counted as meeting the TB case definition; both suggested a true decline in TB in 2009. The population groups with the largest declines were foreign-born persons and children. Continued TB surveillance, including vigilance in suspecting, diagnosing, and reporting TB cases to public health departments, will help clarify the cause of this decline and determine long-term TB trends in the United States.