Evaluation of Booster Effect of Tuberculin Skin Test in Diagnosis of Latent TB in Health Care Workers of Firoozgar Hospital

Tb is still a major problem in public health all around the world. The goal of testing for latent tuberculosis infection is to identify individuals who are at increased risk for the development of tuberculosis and therefore would benefit from treatment of latent TB infection. Tuberculin skin test (TST) has been used to identify individuals with previous sensitization to mycobacterial antigens.. False negative tuberculin skin test results may occur in the setting of biological limitations. Biologic limitations include immunosuppression or natural waning of immunity.. Booster response refers to a positive TST performed one to four weeks after an initial negative TST in the absence of exposure (such as pre-employment screening of healthcare workers).
In this study booster effect was evaluated in health care workers with negative PPD test in Firoozgar hospital at spring and summer 1394. In persons with negative PPD test this test was repeated after 2 weeks.
In 85 cases (80.2%) PPD test was negative .In 21 cases (19.8%) test was positive. In 77 case with negative test second PPD test was performed .After second test 60 cases (78%) had negative result and 17 cases (22%) had positive test .In this study positive result was increased from 19.8% to 35%.
Overall in this study, positive results with two-step method turn from 19.8% to 35%.So two-step method is recommended for accurate diagnosis. Therefore we have concluded that second PPD test is recommend for better diagnosis of latent tuberculosis(TB) in health care workers.