Hi David,
There are several citations for this but here’s the updated 2019 CDC guidelines for TB testing in healthcare workers:
Sosa LE, Njie GJ, Lobato MN, et al. Tuberculosis Screening,
Testing, and Treatment of US Health Care Personnel: recommendations from the National Tuberculosis Controllers Association and CDC, 2019. MMWR
Morb Mortal Wkly Rep 2019;
68:439–443.
Here’s the pertinent section:
"The
risk assessment and symptom evaluation help guide decisions when interpreting test results. For example, health care personnel with a positive test who are asymptomatic, unlikely to be infected with M.
tuberculosis, and
at low risk for progression on the basis of their risk assessment should have a second test (either an IGRA or TST) as recommended in the 2017 TB diagnostic guidelines of the American Thoracic Society, Infectious Diseases Society of America, and CDC. In this
example, the health care personnel should be considered infected with M.
tuberculosis only
if both the first and second tests are positive.”