CDC may drop routine TB skin testing in some areas

Testing in low TB areas leads to false positives

Reacting to declining tuberculosis, the Centers for Disease Control and Prevention (CDC) soon may drop its recommendation for annual TB skin testing of health care workers in areas of low TB prevalence. In revising its 1994 TB guidelines for health care settings, the CDC wants to address the issue of false-positive tuberculin skin tests in areas with little TB in the community.

"For example, in Montana, which has 20 cases a year, it may be difficult to justify doing annual skin testing on every health care worker because the skin test has an inherent false-positive rate in itself," says Renee Ridzon, MD, medical epidemiologist in the CDC division of TB elimination. "The efficiency of the test is not really good in some settings that are using annual skin testing right now."

The system the CDC is considering going to is to test the worker at baseline (e.g., on hire) and thereafter only if there is a known or suspected exposure to TB. There would be no annual or "serial testing" for health care workers in low-prevalence areas, although the exact definition of such areas remains to be clarified.

"We are also trying to streamline the risk categories," Ridzon says. "In the old one, there were five different risk categories. Some of the feedback we have gotten is that this was very confusing for people. We are considering streamlining into just three [e.g. low, medium, and high risk]."

The CDC also is expected to address the issue of respiratory fit-testing in the revisions, but Ridzon declined comment on that aspect. The National Institute for Occupational Safety and Health (NIOSH), a branch of the CDC that certifies respirators, is participating in the guideline revision. Meanwhile, the Occupational Safety and Health Administration (OSHA) is expressing interest in duplicating the CDC revised guidelines in a TB regulatory standard. The CDC guidelines are being revised without consideration to the regulatory implications, Ridzon says. "Given that it is not clear what is going to happen with the [OSHA] TB standard, this needs to be considered a separate publication," she says. "We consider this a document that the CDC and NIOSH are producing."

The CDC recently released a report showing TB in the United States is continuing to decline, though cases in the foreign-born are an ongoing concern.1 During 2000, a total of 16,377 cases (5.8 cases per 100,000 population) of TB were reported to the CDC from the 50 states and Washington, DC. That represents a 7% decrease from 1999 and a 39% decrease from 1992, when the number of cases and case rate most recently peaked in the United States (26,673 cases; 10.5 cases per 100,000 population.)

Public health identification and treatment efforts, and enhanced infection control programs in hospitals are contributing factors to the decline. "We at CDC certainly aren’t receiving as much information, as in the early part of the ’90s for example, of nosocomial transmission of TB." Ridzon says. "It seems like we have imposed infection control measures and that these have been effective. I think that most people in infection control in the country feel that that is the case."

Foreign-born rate seven times higher

Despite the overall decline in TB, the case rate among the foreign-born remains at least seven times higher than native U.S. citizens, according to the CDC report. Of the 16,377 cases in 2000, 8,714 cases (3.5 per 100,000 population) were reported among the U.S.-born; 7,554 (25.8 per 100,000 population) were among the foreign-born. The latter group represents 46% of all cases.

To address the high rate in the foreign-born, the CDC is working with its public health partners to implement TB controls among recent international arrivals and residents along the border between the United States and Mexico. The CDC also is trying to assist TB programs in countries with a high incidence of TB disease, rather than just trying to catch cases at the border.

"Certainly, one of the things we have to avoid with these [revised] guidelines is saying. Every-thing is under control; forget about it,’" Ridzon says. "You don’t want to create a lax sense. You need to keep vigilance up. People need to continue to be thinking about this. It’s difficult, but it’s sort of where we are going in a general sense with TB in the country."

The concern is the "paradox of prevention," which essentially means that the very resources that brought TB under control vanish along with the disease. "As rates go down everywhere, even state TB control programs may lack the resources any longer to put a number of [staff] on TB only," she says. "At the same time, they still have to be equipped to deal with a cluster of cases. This is something we have to address in all aspects of TB control in the United States, not just in hospitals."

Indeed, Ridzon has firsthand experience with the phenomenon, remembering that she was told as a medical resident in the 1980s that she would probably never see a case of TB. In the following years, TB made its bold return. "Having seen that resurgence so recently, [hopefully] there won’t be that much apathy," she says.

Reference

1. Centers for Disease Control and Prevention. Tuberculosis mortality among U.S.-born and foreign-born populations — United States, 2000. MMWR 2002; 51:101-104.