TB drops for fifth straight year in 1997 data for U.S.

Controls work, but foreign-born cases climb to 39%

In 1997, the total number of reported tuberculosis cases in the United States decreased for the fifth consecutive year, the Centers for Disease Control and Prevention reports.¹

There were 19,855 cases of TB (7.4 cases per 100,000) reported to the CDC from the 50 states and the District of Columbia, a 7% decrease from 1996. The 1997 total also represents a 26% decrease from 1992, when the number of cases peaked during the resurgence of TB in the United States.

"The decline in overall number of reported TB cases has been attributed to stronger TB-control programs that emphasize promptly identifying persons with TB, initiating appropriate therapy, and ensuring completion of therapy," the CDC says. "The resulting decline in cases among U.S.-born persons probably reflected reduced community transmission of TB, particularly in areas with a high incidence of AIDS. In comparison, the relatively stable number of cases among foreign-born persons indicated that most cases of active TB disease among foreign-born persons residing in the U.S. result from infection with TB in the person's country of birth."

While the overall number of TB cases continued to decrease, underlying trends differed by region and by population characteristics. In 1997, six states - California, Florida, Illinois, New Jersey, New York, and Texas - reported 57% of all TB cases. Still, the number of cases reported from each of those states has decreased substantially since 1992.

A breakdown of the findings reveals a substantial decrease in cases among U.S.-born people and a small increase in the number of cases among the foreign-born. The number of foreign-born cases has increased only 6% since 1992, but the cases occupy an increasingly large proportion of the total due to continued drops in U.S.-born cases. For example, 27% of U.S. TB cases in 1992 were among foreign-born people, but that segment accounted for 39% of cases in 1997.

"The TB case rate for foreign-born persons has remained at least four to five times higher than that for U.S.-born persons," the CDC reported.

To reduce active TB disease among the foreign-born in the U.S., the CDC is working with state and local health departments to improve case-finding and prevention. However, not all foreign-born people have the same risk for active TB disease. For example, people from countries with established market economies and from most former socialist countries of Europe are at low risk for active TB disease and may benefit least from screening.

Outbreaks of multidrug-resistant TB, particularly among HIV-infected people, contributed to the resurgence of TB in the late 1980s and early 1990s. Since the CDC began monitoring anti-TB drug resistance through the national TB surveillance system in 1993, levels of isoniazid resistance have been relatively stable, and the number and proportion of MDR-TB cases has decreased. During 1997, 42 states reported drug-susceptibility results for at least 75% of culture-positive cases. Of those, 963 isolates (7.6%) were resistant to at least isoniazid, and 171 (1.3%) were classified as MDR-TB, with resistance to at least isoniazid and rifampin. Of the 42 states, 27 reported at least one MDR-TB case. However, 47% of all MDR-TB cases were reported in New York (47 cases) and California (34 cases), the CDC reported.

Reference

1. Centers for Disease Control and Prevention. Tuberculosis morbidity - United States, 1997. MMWR 1998; 47:253-257.