Prevalence of latent tuberculosis infection in German radiologists

Healthcare workers have an increased risk of tuberculosis infection compared with the general population. There have been few attempts to quantify the prevalence of latent tuberculosis infection amongst German healthcare workers, due to inadequacy of the current tuberculin skin test (TST). Therefore, it was our aim to investigate the prevalence of latent tuberculosis in this cohort using a tuberculosis-specific ELISpot (T-SPOT.TB) test and to compare the performance of this test to that of the TST. Ninety-five healthy participants working in departments of radiology were examined by ELISpot, lymphocyte transformation test and TST. For cellular in-vitro tests, tuberculosis-specific peptides and purified protein derivate (PPD) were used as antigens. These tests were combined with a questionnaire on prior tuberculosis exposure. Out of 95 healthcare workers, only one (1%) was defined as positive by T-SPOT.TB, 92 (97%) by PPD-ELISpot, 78 (82%) by PPD-lymphocyte transformation test and 32 (34%) by TST. Multivariate analysis showed that the TST was significantly affected (P<0.0001 and P=0.001, respectively) by foreign birth and prior skin testing. The T-SPOT.TB test results were independent of foreign birth, prior skin testing and prior vaccination against tuberculosis. In contrast to the TST, T-SPOT.TB appears to be an accurate and useful tool to track tuberculosis infection in this at-risk group. With only one of 95 participants having acquired latent tuberculosis, these preliminary results argue for a low incidence of latent tuberculosis in German radiologists.