False! Employee health workers may say that people who have gotten the BCG vaccination–usually from Asia, Africa, or the Caribbean–do not have reliable PPD readings and therefore need chest x-rays. One magazine article reports: “Current Occupational Safety and Health Administration (OSHA) regulations do not require periodic chest x-rays for a health-care worker who is PPD-positive unless symptoms develop.”
Furthermore, according to Ethnomed:
“Prior vaccination with BCG is not a contraindication to TB skin testing, and the CDC guidelines recommend ignoring BCG status when interpreting skin test results and selecting candidates for latent TB treatment. Although BCG vaccination can turn a skin test positive, reactivity due to BCG vaccination wanes over time. If it has been more than 5 years since vaccination, a positive skin test is more likely due to TB infection than vaccination. Furthermore, the larger the size of the PPD reaction, the less likely it is due to BCG. A recent meta-analysis found that reactive skin tests more than 15 years since vaccination or with more than 15 mm of induration were unlikely to be due to prior BCG vaccination.
Interferon-based blood tests such as the QuantiFERON® -TB Gold avoid the possibility of false-positives occurring from BCG vaccination, since cross-reactivity does not occur.”
Be warned that the Quant Gold may come back as “indeterminate” or “borderline” and then you may be in a bit of a pickle and have to get a chest x-ray anyway.
Questions you should make sure to ask someone who has had a past positive PPD:
1. How long ago was it?
2. Have you ever received the BCG vaccine?
3. Did you ever receive treatment for latent TB? (isoniazid)
4. Have you ever had a chest x-ray previously?