HIV-INFECTION, TUBERCULOSIS, AND TUBERCUL IN SKIN-TEST IN SWITZERLAND

Background: The usefulness of the tuberculin skin test (TST) for HIV-i nfected subjects may be questioned because false-negative results are increasingly common with advanced immune deficiency. The objectives of this research were thus to describe the use and the results of TST am ong patients with HIV infection in Switzerland and to measure the usef ulness of isoniazid preventive chemotherapy and the incidence of tuber culosis (TB) relative to TST and CD4 cell count at the time of TST. De sign: Prospective multicentric cohort study of HIV infected patients; comparison of patients tested and non-tested, and of those with positi ve and negative TST. Multivariate comparison (Cox model) of TB inciden ce taking into account TST results and CD4 cell count at the time of T ST Results: Out of 5802 patients followed up in the Swiss HIV cohort s tudy as of September 1994, 34.6% were tested. Native Swiss were more l ikely to be tested than patients from high TB prevalence countries (36 % vs 21% of native Africans). Patients registered after 1990 were more often tested than before (50% vs 26%). Of 2010 tested patients, 6.8% had a >5 mm induration. African patients were more frequently TST posi tive (26%) than Swiss nationals (6%). Among patients with CD4 >500 per mm(3) at the time of the test, 16% were TST positive compared to 1% o f those with CD4 <200 per mm(3). Out of 25 cases of tuber tuberculosis among tested patients, 84% (21) occurred among TST-negative patients. Tuberculosis incidence among TST-negative patients with CD4 greater t han or equal to 200 per mm(3) at the time of the test was 0.3 per pers on-year. Ln comparison, the adjusted relative risk of tuberculosis amo ng TST-positive patients with CD4 greater than or equal to 200 per mm( 3) was 5.5 (95% confidence interval [CI]: 1.2-23.9) and 6.6 (CI: 2.3-1 9.0) among TST negative patients with CD4 <200 per mm(3). Conclusion: Despite its usefulness, TST is often performed too late and is therefo re difficult to interpret. TST should be done as early as possible. Am ong patients with CD4 <200 per mm3, a negative TST should not preclude the use of preventive chemotherapy, particularly in those originally from countries with a high incidence of tuberculosis.