Latent TB infection (LTBI) generally results in the conversion of the TB skin test (TST) from negative to positive within two to ten weeks after exposure. Persons with a positive TST are infected, but if they have no symptoms and a negative chest x-ray, they cannot transmit TB to others. They are, however, at risk of progressing from latent to active disease unless they receive anti-TB therapy. Health care workers who convert during employment should: 1) complete a symptom-screen questionnaire, 2) have a CXR — within 7 days is recommended, and 3) be seen by a health care provider or local public health department for treatment. A person with one unexplained symptom on the questionnaire should be excluded from work until active TB has been ruled out. An annual chest x-ray for asymptomatic TST positive employees is not necessary nor recommended.
To identify employees who may have LTBI and to establish a baseline for annual or exposure testing, all new employees should have a two-step TST administered and interpreted prior to beginning work. A TST is not required if there is written documentation of 1) a positive TST on a 1st or 2nd test; a negative 2-step within 90 days prior to employment and 3) history of active TB disease. While several TST screening tests are available, it is important for a facility to stay with one brand or method of TST since variations in reactions could render comparisons with previous reactions inaccurate.
The TST is based on the Mycobacterium tuberculosis ability to produce a delayed-type hypersensitivity skin reaction to certain components of the organism. Components of the bacterium are the core elements of the classic tuberculin PPD. A PPD skin reaction is initiated when specialized immune cells, called T-cells, which have been sensitized by prior infection, are recruited to the skin site. There they release chemical messengers called lymphokines, which induce induration (a hard, raised area with clearly defined margins at and around the injection site) through local vasodilation, edema, fibrin deposition, and other inflammatory cells.
The FDA has approved the use of QuantiFERON-TB Gold Test (QFT) for detecting active TB disease or LTBI. The 2005 Department of Health Services and California TB Controllers Association Joint Guidelines for the Prevention and Control of TB in California Long-Term Health Care Facilities require approval by the facility's patient care committee for use of QFT on new admissions and a grant of program flexibility from Licensing and Certification for use on employees, since the TST is required by CCR Title 22 §72535.
Symptoms of active TB include but are not limited to: Coughing up blood, hoarseness lasting three weeks or more, persistent cough lasting three weeks or more, unexplained, excessive fatigue, unexplained, persistent fever lasting three weeks or more, unexplained, excessive sweating at night, unexplained weight loss.