Real and apparent tuberculin skin test conversions in a group of medical students

To evaluate tuberculin skin test (TST) conversions among a group of medical students.

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.

County hospital and associated medical school.

Medical students, after their third year in medical school.

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.

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.