TUESDAY, Nov. 11 (HealthDay News) -- Running contrary to what is occurring elsewhere in the world, the number of drug-resistant tuberculosis cases in the United States has declined dramatically in the past 15 years. But U.S. government officials caution that the more than 13,000 other cases of TB in America in 2007 need to be reduced as well.

TB is the leading cause of infectious disease death among adults worldwide, and drug-resistant TB (which includes multidrug-resistant TB and XDR-TB) is an increasing threat, with an estimated 489,000 new cases in 2006.

In this study, researchers from the U.S. Centers for Disease Control and Prevention analyzed 15 years of U.S. surveillance data from 1993 to 2007 and found that 83 cases of XDR-TB were reported during that time. The number of XDR-TB cases per year declined from 18 (0.07 percent of 25,107 TB cases) in 1993 to two (0.02 percent of 13,293 TB cases) in 2007.

Of the 40 XDR-TB cases reported from 1993 to 1997, 25 (62 percent) were in HIV-infected patients, compared with six of 43 cases (14 percent) reported in 2007.

Of the 83 XDR-TB cases reported in the United States from 1993 to 2007, most patients were ages 25 to 44, male (64 percent), U.S.-born, and unemployed (53 percent). There were 33 Hispanic patients (44 percent), and three cases occurred among health-care workers. Compared with drug-treatable TB cases, patients with XDR-TB were more likely to be Hispanic and correctional facility inmates.

The study also found that 26 XDR-TB patients (35 percent) died during treatment. Of those, 21 (81 percent) had HIV. Death rates for XDR-TB patients were nearly two times higher than among MDR-TB patients and more than six times higher than among drug-treatable TB patients. HIV was a major factor in both the occurrence and outcomes of XDR-TB cases, the researchers said.

"Preventing the further emergence of drug resistance is paramount and must include not only TB program strengthening to ensure that patients complete their treatment regimen but also general health system interventions to improve infection control. Greater vigilance regarding drug resistance must include systematic second-line drug susceptibility testing according to published guidelines. Lessons gained from MDR-TB in the 1990s should be applied: Patients must be identified early, treated effectively, and assisted to complete treatment, and infection control precautions must be in place to prevent further emergence and transmission of XDR-TB," the researchers concluded.

The study was published in the Nov. 12 issue of the Journal of the American Medical Association.

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