Less TB testing means more time for EH

Low risk hospitals must be ready to retest

Screening for latent tuberculosis, once a key function of hospital employee health, has been transformed by new guidelines and new blood tests. The changes have greatly reduced the use of skin testing and freed employee health professionals to perform other important tasks, but they also have created some new, sometimes difficult, issues.

Until recent years, hospitals routinely screened all employees with a TB skin test. But testing of employees in hospitals that rarely, if ever, see a case of tuberculosis are most likely to identify employees with other risk factors for TB or to produce false positives, TB experts say.

“It just uses our resources in very inefficient ways,” says Lisa Dyrdahl, RN, BSN, employee health coordinator at Valley Medical Center in Renton, WA.

In 2005, the Centers for Disease Control and Prevention issued guidelines that advised health care facilities to conduct an annual risk assessment for TB. Low-risk facilities — defined as fewer than three TB cases a year in hospitals of less than 200 beds and fewer than six in hospitals of 200 beds or more — do not need to conduct annual screening. They provide baseline testing and annual symptom screens for employees with previous positive tests. (See box, below.)

Valley Medical Center ended its annual TB screening in 2009. Drydahl reviewed the prior six years and found that the hospital had consistently been at low risk. Now she spends more time working with the human resources department to help employees return to work after injury. Employees still receive information about TB in their annual online infection control competency program.

“We have to streamline our jobs as much as possible and where possible eliminate things that aren’t giving us benefit,” she says.

From low risk to moderate

As hospitals limit their TB screening programs, there’s one caveat: TB risk might not always remain at a low level.

At the Marshfield (WI) Clinic, Bruce Cunha, RN, MS, COHN-S, manager of employee health and safety, enjoyed the staff time he gained by ending the skin testing program. But then in 2012, the main clinic facility saw three patients with tuberculosis, which put it in the moderate risk category.

Even worse, two of those cases were not promptly reported to employee health, so there was no opportunity to assess who may have been exposed and to target TB screening. Cunha is now gearing up to test 2,500 employees using the QuantiFERON-TB Gold test, one of two available blood tests.

“If you know who was exposed, you can break down your risk by department,” he says. “Unfortunately, now we’re at a point where we have to test everyone.”

Cunha’s advise: Maintain the ability to ramp up your screening program, if necessary. Even a low-risk facility can see the occasional TB patient. “I would recommend having a contingency plan in place,” he says.

The Marshfield lab performs the QuantiFERON tests, so Cunha will need to find funds for the lab kits. Switching back to skin testing would be even worse, he says, because it is time-consuming and would require new training for the nurses reading the tests.

Retest if you question result

Sometimes an employee tests positive in the annual tuberculosis screen with a blood test, but the result seems hard to believe. The employee has had no known exposure, has no personal risk factors, such as foreign travel or volunteering in a homeless shelter, and the measure is just above the cutoff. What should you do?

Repeat the test, says Thomas Navin, MD, chief of the surveillance, epidemiology and outbreak investigations branch in the Division of TB Elimination of the Centers for Disease Control and Prevention. Testing a low-risk population increases the likelihood of false positives, he says.

“When you’re doing a screening program of a large number of people, you would expect most of them to be negative,” he says. “When someone turns up positive with no change in their risk classification, it’s reasonable to question that positive test.

“If that second test is negative, then our data suggests that all other tests would be negative as well,” he says. “The blood tests are complicated tests and there are many steps where variability can enter.”

Some occupational health experts have suggested retesting employees who are just above the cutoff to reduce the risk of false positives with interferon gamma release assays (IGRAs). (See HEH, October 2012, p. 114.)

CDC funded a large study of serial TB testing of health care workers. Although the results have not yet been published, Navin says the study doesn’t support altering the cutoff.

“So far, it looks like the issue of the best cutoff is not really the important issue,” Navin says. “The important issue is the variability of the test in a low-risk population. Changing the cut-off really doesn’t change that fundamental problem of the blood test, [which is] the unexpected variability in low-risk persons.”

Many occupational health professionals already make a judgment call on TB tests. At the Mayo Clinic in Rochester, MN, occupational medicine physician William Buchta, MD, MPH, retests employees if they are low-risk and have TB test results near the cutoff. “If it’s a low-probability population, it better be a pretty positive test to convince me they actually have disease,” he says.

What if the health care worker is foreign-born and comes from a country in which tuberculosis is endemic? CDC does not recommend treating health care employees differently based on ethnicity or national origin. Navin notes that foreign-born health care workers receive TB screening when they first are hired by a health care facility, as do all employees.

“Our surveillance indicates that the highest risk [of having a positive TB test] is right after they arrive [in the United States],” he says. “It drops substantially in the [subsequent] years.”

TB risk assessment and screening issues

In its 2005 guidelines for preventing tuberculosis transmission in health care facilities, the Centers for Disease Control and Prevention sets the following definitions. (High risk at all facilities is defined as ongoing evidence of TB transmission, or a hospital-based TB outbreak. The high-risk designation can be limited to a defined area or specific group of health care workers with potential exposure to the outbreak cases. Baseline testing should occur of all health care workers at all facilities.)

Inpatient hospitals of less than 200 beds and outpatient: Low risk is fewer than 3 TB patients in a year, moderate risk is 3 or more TB patients.

Inpatient hospitals of more than 200 beds: Low risk is fewer than 6 TB patients in a year, moderate risk is 6 or more TB patients.

Laboratories: Low risk laboratories do not manipulate clinical specimens that might contain M. tuberculosis. Moderate risk laboratories do manipulate such specimens.

Other considerations: CDC notes that settings that treat a high-risk population, such as HIV or immunocompromised patients or patients with multi-drug resistant TB, might need to be considered moderate risk even if they meet the definition of low risk.

Serial screening: None (after baseline) for health care workers in low-risk settings. At least yearly for health care workers in medium-risk settings. Every 8 to 10 weeks in high-risk settings until the ongoing transmission has ended. Then the setting is considered medium risk for at least a year.

Editor’s note: The CDC guidelines for preventing TB transmission in health care settings are available at http://ow.ly/k9KBP