Real and Apparent Tuberculin Skin Test Conversions in a Group of Medical Students

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Abstract
Objective: To evaluate tuberculin skin test (TST) conversions among a group of medical students. Design: Questionnaire sent to a medical school class in whom a cluster of TST conversions was noted, and interview and repeat TST of students with conversion. Setting: County hospital and associated medical school. Subjects: Medical students, after their third year in medical school. Results: Of 165 students in the class, 115 (70%) responded; 10 reported TST conversions between the beginning of the third and the fourth year. Seven of 10 were interviewed, and all 10 were retested. Five students, all in a cohort who tested each other during a clinical clerkship with a tuberculin material previously reported to be associated with a high rate of false-positive TSTs, were TST negative on repeat. Five had persistently positive TSTs. One was exposed during a psychiatry clerkship to a resident with pulmonary tuberculosis. Four students appeared to have converted their TST during their third year in medical school. All four did their medicine clerkship at a large county hospital (P<0.02; odds ratio = 16.4) that had few infection control measures in place for tuberculosis isolation during the time of their exposure. Conclusions: We recommend that medical students, as well as other healthcare professions students, be educated about infection control practices and skin tested at least annually during clinical training years.