New TB blood tests may up accuracy of HCW screening

No false-positives due to BCG vaccination

The availability of new diagnostics for latent tuberculosis infection signals a sea change in the way hospitals conduct annual testing of health care workers, a veteran TB controller emphasizes.

The Centers for Disease Control and Prevention has published new TB guidelines advising that blood assays for M. tuberculosis(BAMT) can be used as an alternative to the traditional skin test (TST) method.1 The development was hailed by Lee Reichman, MD, the veteran TB clinician and author who coined the term "the U-shaped curve of concern" to describe how TB has always resurged historically once efforts to fight it wane. The executive director of the New Jersey Medical School National Tuberculosis Center, Reichman has long noted that technological innovations against TB have been virtually unheard of.

"The trouble with the TST is that it requires two visits and hospitals employees don’t like to cooperate with that kind of thing," he tells Hospital Infection Control. "If they test positive, it can be because they were infected with TB bacillus or they had BCG [vaccine] in their own country, or they are infected with cross-reacting mycobacterium. Speaking for my hospital, [this can] be extraordinarily difficult to deal with. Here we have this new, one-step test. You just draw blood, and it’s only positive due to infection with TB. It doesn’t cross react with BCG or with most non-TB mycobacterium."

In the United States, vaccination with the BCG TB vaccine is not recommended routinely for anyone, including health care workers or children, the CDC guidelines state. However, the vaccine is used in many other countries and can lead to boosting in baseline two-step testing in certain persons. "Distinguishing a boosted TST reaction resulting from BCG vaccination [a false-positive TST result] and a TST result because of previous infection with M. tuberculosis [true-positive TST result] is not possible," the CDC guidelines state. "Infection control programs should refer HCWs with positive TST results for medical evaluation as soon as possible. . . . The whole-blood interferon gamma release assay [IGRA], QuantiFERON®TB Gold test (QFTG) [Cellestis Limited, Carnegie, Victoria, Australia], is a Food and Drug Administration-approved in vitro cytokine-based assay for cell-mediated immune reactivity to M. tuberculosis and might be used instead of TST in TB screening programs for HCWs."

Reference

  1. Centers for Disease Control and Prevention. Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings, 2005. 2005/54(RR17); 1-141.