Thursday, March 22, 2007

Trends in Tuberculosis Incidence: MMWR

In 2006, a total of 13,767 tuberculosis (TB) cases (4.6 per 100,000 population) were reported in the United States, representing a 3.2% decline from the 2005 rate. This report summarizes provisional 2006 TB incidence data from the National TB Surveillance System and describes trends since 1993. The TB rate in 2006 was the lowest recorded since national reporting began in 1953, but the rate of decline has slowed since 2000. The average annual percentage decline in the TB incidence rate decreased from 7.3% per year during 1993--2000 (95% confidence interval [CI] = 6.9%--7.8%) to 3.8% during 2000--2006 (CI = 3.1%--4.5%). Foreign-born persons and racial/ethnic minority populations continue to be affected disproportionately by TB in the United States. In 2006, the TB rate among foreign-born persons in the United States was 9.5 times that of U.S.-born persons.* The TB rates among blacks, Asians, and Hispanics† were 8.4, 21.2, and 7.6 times higher than rates among whites, respectively. The slowing of the decline in the overall national TB rate and the inability to effectively address persistent disparities in TB rates between U.S.-born and foreign-born persons and between whites and racial/ethnic minority populations threaten progress toward the goal of eliminating TB in the United States. In 1989, CDC and the Advisory Committee for the Elimination of Tuberculosis issued a strategic plan for the elimination of TB, setting an interim target case rate of 3.5 per 100,000 population by 2000 and ultimately the elimination of TB (i.e., <1 case per 1 million population) in the United States by 2010 (1).

TB is a nationally notifiable disease. Health departments in the 50 states and District of Columbia (DC) electronically report to CDC any TB cases that meet the CDC and Council of State and Territorial Epidemiologists case definition.§ Reports include the patient's race, ethnicity (i.e., Hispanic or non-Hispanic), treatment information, and drug-susceptibility test results if available. For this analysis, CDC calculated national and state TB rates (2) and rates for foreign-born and U.S.-born persons (3) and racial/ethnic populations (4) by using current U.S. census population estimates for the years 1993 through 2006.

In 2006, TB incidence rates in the 51 reporting areas ranged from 0.8 (Wyoming) to 12.6 (DC) cases per 100,000 population (median: 3.4 cases). Thirty states had lower rates in 2006 than 2005; 20 states and DC had higher rates (Table 1). In 2006, for the second consecutive year and the second time since national reporting began, approximately half of states (26 of 50) had TB rates of <3.5 per 100,000 (Figure 1); however, 11 of those 26 states had higher rates of TB in 2006 than in 2005. Seven states (California, Florida, Georgia, Illinois, New Jersey, New York, and Texas) reported more than 500 cases each for 2006; combined, these seven states accounted for 60% (8,259) of all TB cases.

Among U.S.-born persons, the number and rate of TB cases continued to decline in 2006. The U.S.-born TB rate was 2.3 per 100,000 population (5,924 or 43.3% of all cases with known origin of birth), representing a 7.0% decline in rate since 2005 and a 68.6% decline since 1993 (Figure 2).

Among foreign-born persons, the number of TB cases increased in 2006, but the rate decreased. The foreign-born TB rate in 2006 was 21.9 per 100,000 population, representing a 0.5% decline in rate since 2006 and a 35.8% decline since 1993. As the rate of decline in TB cases among foreign-born persons lagged behind the decline in TB cases among U.S.-born persons, the foreign-born to U.S.-born rate ratio increased 7.0%, from 8.9 in 2005 to 9.5 in 2006. In 2006, approximately half (55.6%) of TB cases among foreign-born persons were reported in persons from five countries: Mexico (1,912), the Philippines (856), Vietnam (630), India (540), and China (376).

In 2006, for the third consecutive year, more TB cases were reported among Hispanics than any other racial/ethnic population. Among persons with TB whose country of birth was known, 95.6% (3,126 of 3,269) of Asians, 74.7% (3,024 of 4,050) of Hispanics, 29.9% (1,110 of 3,712) of blacks, and 17.8% (427 of 2,404) of whites were foreign born. From 2005 to 2006, TB rates declined for all racial/ethnic minorities except American Indians/Alaska Natives and Native Hawaiians or Other Pacific Islanders¶ (Table 2).

Human immunodeficiency virus (HIV) contributes to the TB pandemic because immune suppression increases the likelihood of rapid progression from TB infection to TB disease. From 2005 to 2006, among TB cases with HIV status reported,** the percentage of TB cases with HIV infection decreased 4.4% (from 13.0% to 12.4%), but the percentage of TB cases with unknown HIV status increased 10.3% (from 28.7% to 31.7%).†† The decline in the percentage of TB cases with HIV infection might reflect incomplete reporting of HIV test results attributed to a lack of HIV testing or HIV reporting.

A total of 124 cases of multidrug-resistant TB (MDR TB)§§ were reported in 2005, the most recent year for which complete drug-susceptibility data are available.¶¶ The proportion of MDR-TB cases remained constant at 1.2% from 2004 (129 of 10,846 TB cases) to 2005 (124 of 10,662). In 2005, MDR TB continued to disproportionately affect foreign-born persons, who accounted for 101 (81.5%) of 124 MDR-TB cases.

The recommended length of drug therapy for most types of TB is 6--9 months. In 2003, the latest year for which treatment data are complete, 82.7% of patients for whom <1 year of treatment was indicated completed therapy within 1 year, below the Healthy People 2010 target of 90% (objective 14-12).

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