Latest TB testing guide set forth by ATS, CDC, IDSA

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Dr. Woods

Dr. Woods points out that diagnosing active tuberculosis is entirely different from diagnosing latent infection. “It doesn’t hurt to get an IGRA or do TST, but they won’t make the diagnosis. You have to do culture for M. tuberculosis and a smear and in some cases a nucleic acid amplification test.”

Once a patient has a positive TST or IGRA, the clinician has to rule out active disease by asking about symptoms—cough (particularly if the patient is coughing blood), fever, and weight loss. Next would be a chest x-ray. “If any of these investigations is positive, you need to continue with testing for disease,” Dr. Woods says. “It is crucial to rule out active disease before you treat for infection because the most popular choice [for latent infection] is a one-drug regimen, which you wouldn’t use for active TB.”

There is one change in the workup of active TB. “We did recommend that people use NAAT [nucleic acid amplification tests] to try to more rapidly identify M. tuberculosis in respiratory specimens,” Dr. Daley says. “They were previously recommended to be used but they weren’t used in the U.S. as much as they should. We were quite delayed in adopting rapid molecular tests. I think we are catching up now.” Appropriate NAATs, the guideline says, include the Hologic Amplified Mycobacteria Tuberculosis Direct test and the Cepheid Xpert MTB/RIF test. The Cepheid test detects presence of M. tuberculosis and rifampin resistance mutations in two hours.

Could the policies to identify and deport the undocumented in the U.S. detrimentally affect public health programs to screen those with a risk of having latent infection and TB disease? “I’m pretty sure that’s going to happen,” Dr. Daley says. “What we in public health provide is a safe haven for people who require care. We have used that to find latent infection and TB. We could even discuss with people that treatment will take so many months and ask whether they would be here for that time, and they could answer truthfully. Now I don’t think they will show up.”
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William Check is a writer in Ft. Lauderdale, Fla.