CDC eyes scaled back skin tests for some areas
Low-prevalence settings might need only baseline
The recommended frequency for skin-testing of health care workers in low-prevalence areas should be scaled down from every year to just a baseline test, according to Renee Ridzon, MD, medical epidemiologist in the Centers for Disease Control and Prevention’s Division of TB Elimination (DTBE). Under the new system being considered, workers in low-prevalence settings would be tested only at baseline (e.g., on hire) and thereafter only if there is a known or suspected TB exposure. This change would do away with "serial testing" for health care workers in low-prevalence areas, although the exact definition of such areas remains to be clarified, Ridzon adds.
The proposal is one now being considered by Ridzon and other TB experts at the DTBE charged with revising the 1994 infection control guidelines for health care workers. The new guidelines should be out by the end of the year.
Response to concern over false positives
The proposed changes represent a response to the issue of false-positive tuberculin skin tests in areas with little TB in the community, Ridzon says. "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. The efficiency of the test is not really good in some settings that are using annual skin-testing right now."
Another change being considered for the new guidelines is a streamlining of risk categories. In the old paradigm, there were five different risk categories, Ridzon notes. "Some of the feedback we have gotten is that this was very confusing for people," she adds. "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. The National Institute for Occupational Safety and Health (NIOSH), a branch of the CDC that certifies respirators, is participating in the guideline revision.
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 to the decline.
"We 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 as if 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."
Despite the overall decline in TB, the case rate among the foreign-born remains at least seven times higher than the rate for 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 federal agency is also 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. Everything is under control; forget about it,’" Ridzon say. "You don’t want to create a sense of laxity; we need 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."
Ridzon has firsthand experience with the phenomenon. As a medical resident in the 1980s, she recalls being told she would probably never see a case of TB. By the latter part of the decade, the incursion of HIV — coupled with severe cutbacks to the nation’s public-health system — had created tinderbox conditions. Deaths from TB soared, and suddenly the disease was front-page news.
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.
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