Routine skin testing yields undetected TB patients

Discontinued practice worthwhile in some hospitals

Tuberculin skin testing used to be routine for newly hospitalized patients, but the practice was dropped when TB rates dropped in the early 1970s. The experience of at least one hospital suggests, however, that resurrecting this type of testing may be worth the time and effort in some settings.

Researchers at a 1,000-bed university hospital in Missouri began offering skin testing to all but its obstetric patients and newborns during a five-day period in 1992. Of the 279 patients receiving the test, new positive skin tests were identified in 19 patients. Although it may have produced even more positive results, patients who tested negative were not given second tests to look for the booster effect.

Radiographs of the positive patients identified six who had pulmonary infiltrates and who were put in isolation. One patient was treated for active TB, and five others were given isoniazid prophylaxis. On average, the hospital admits 10 to 20 patients per year with culture-positive TB, according to the study, published in Infection Control and Hospital Epidemiology.1

"Our results suggest that the method may be quite effective, as it led to the isolation of six patients who otherwise would not have been recognized as potential sources of TB," the authors conclude. "In addition to the direct identification of patients at risk for having TB disease, prompting a more intensive evaluation, we suspect that routine placement of skin testing would lead to a higher overall awareness of TB as a problem."

Lead author, Keith Woeltje, MD, PhD, medical director at Barnes Hospital in St. Louis and professor of medicine at Washington University School of Medicine, tells TB Monitor that his hospital did not routinely skin test patients nor did he know of any that did. However, until now there have been no studies showing that routine testing could be effective. "One of the reasons we wanted to get this data out is because it hasn’t been done recently in any hospital, and so we have had no idea of what the underlying prevalence of skin testing would be."

Skin testing to control TB

The fact that a half dozen patients were detected for TB through skin testing and had to be treated, points to its potential as a prevention and control tool, especially considering that the hospital has a low incidence of TB, he notes. Moreover, most of the six patients were elderly and had latent infection, suggesting that they may have been more prone to not being diagnosed if skin testing were not utilized.

"I don’t think we are seeing a lot of people who are positive because they are inner city dwellers or recent converters but rather people who are positive from long-ago exposures," he says.

The study was designed to evaluate risk factors for a positive skin test. At Barnes, which has a heterogenous caseload that includes indigent and tertiary care referral patients, risk factors included African American background, age, alcohol abuse, and peptic ulcer disease. Foreign birth was not a factor in this population as only six foreign-born patients were tested during the study period. In another significant finding, the study showed that one-third of the patients were anergic, with all patients HIV-positive and half of all patients on steroids being anergic.

Before deciding whether to implement routine skin testing of patients, a facility may want to skin test for a limited time, similar to what was done in the study, to see what the results are, Woeltje says. "Before an institution did it full time, it would probably want to do what we did and do it for a couple of weeks several times a year," he explains, adding that areas where TB is endemic may find it especially worthwhile. Also, a hospital may find it more advantageous to limit routine skin testing to specific patient populations, such as those on non-surgical services, to maximize the usefulness of screening.

Train staff to document test results

A hospital considering routine skin testing of patients must have a system in place to train staff to not only administer and read the tests but to make sure they are documented, the authors add. The study did not include a cost-benefit analysis because most of the legwork was performed by medical students, Woeltje says. As he envisions it, a nurse would perform the test as part of his or her admissions duties, ensuring that testing would be routine and cost-effective.

"I don’t foresee it being a high-cost thing if it were done on a regular basis and nurses were trained," he says. "The additional time would be minimal, and the reagents themselves are relatively inexpensive compared to the cost of hospitalizing a patient."

One added benefit that would be hard to measure would be the heightened awareness about TB that a routine skin testing program would bring to a facility, he adds.

Reference

1. Woeltje K, Kilo C, Johnson K, et al. Tuberculin skin testing of hospitalized patients. Infect Control Hosp Epidemiol 1997; 18:561-565.