Tuberculin Skin Testing in Medical Students: A Survey of U.S. Medical Schools

Methods

In May 1992, we mailed a 20-item survey to each of the 126 Deans of U.S. medical schools listed in the Directory of the American Association of Medical Colleges [8]. If we received no reply from the Dean or his or her designee within 3 weeks of the first mailing, we sent a second copy of the survey. The questionnaire inquired about the medical school's policies on tuberculin skin testing at matriculation as well as during medical school. We asked for information on skin-test conversions in medical students and specifically asked for an estimate of the yearly rate of skin-test conversion in the medical student body. Annual incidence rates of tuberculosis for the areas in which medical schools were located were obtained from the CDC [9]. If the medical school was located in a city for which city incidence rates were available from the CDC (all cities with 250 000 or more residents), the city incidence rate was used. Otherwise, we used the incidence rate from the state in which the school was located. Probability values were calculated using chi-square analysis. Confidence intervals were calculated as the mean ± 2 times the standard error.

Results

We received 101 completed surveys, a response rate of 80%. We received responses from medical schools located in 41 (93%) of the 44 states that contain medical schools, as well as from medical schools located in Puerto Rico and the District of Columbia. The person who completed and returned the survey was most commonly an Associate or Assistant Dean of Students (46%) or a Director of Student Health (41%).

Overall, only 41% (n = 41) of all respondents required yearly tuberculin skin testing during medical school. Of the 13 schools with local tuberculosis incidence rates that were less than 50% of the national average (that is, fewer than 5 cases per 100 000 persons), 1 (8%) required annual testing. Of the 26 schools with local incidence rates that were 50% to 100% of the national average (that is, 5 to 10.2 cases per 100 000 persons), 8 (31%) required annual testing. Of the 34 schools with local incidence rates 100% to 200% of the national average (that is, 10.2 to 20.4 cases per 100 000 persons), 16 (47%) required annual testing. Of the 28 schools with local incidence rates greater than or equal to twice the national average, 16 (57%) required annual testing.

Fifty-five percent of schools reported that purified protein derivative conversions had been documented in their students during the past 6 years. Seventy-five (74%) respondents provided estimates of the annual conversion rate in their students (based on both required and voluntary testing). Schools with local incidence rates more than twice the national average tended to be over-represented in this respondent group compared with other schools (82% compared with 71%), but the difference was not statistically significant (P = 0.26). Most schools reported annual conversion rates of 0% to 2%, but annual conversion rates as high as 10% were also reported (Figure 1). The mean estimated annual conversion rate reported by the 75 schools that provided the rate was 1.8% (95% CI, 1.28% to 2.24%), with a median of 2%. Eighty percent of respondents indicated that it was moderately to very likely that their medical students would encounter patients from populations at high risk for tuberculosis, and 59% reported an increase in tuberculosis cases in their hospitals.

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Figure 1. Respondents were asked to estimate the yearly rate of skin-test conversion in the medical student body. Estimated tuberculin skin-test conversion rates in medical students.

Discussion

Our survey results are compatible with the extant data suggesting that tuberculosis is a growing and real risk for health care workers. The estimated purified protein derivative conversion rates among medical students reported here are substantial. Although these conversion rates are predominantly reports by Associate Deans of students or by Directors of Medical Student Health Services rather than data from medical students, the rates are consistent with the national increase in tuberculosis, the reported likelihood that students will encounter patients at risk for tuberculosis, the data on medical housestaff conversion rates [10], and the risk for tuberculosis in the geographic area where the schools are located. More worrisome is that these conversion rates may well be underestimated because nearly half of the medical schools in this survey do not require routine yearly testing and, therefore, are at risk for missing skin-test conversions that occur during medical school. Even if these estimated conversion rates are imprecise, most schools (55%) reported that they are experiencing at least some cases of purified protein derivative conversions in their students; despite this, the tuberculin skin testing policies of most schools (58%) are inadequate to provide surveillance of this population of health care workers and are not consistent with published CDC standards.

The main limitation of our study is that the information we collected was self-reported by the Dean or his or her designee, which could lead to recall and selection biases (limitations of all survey studies). Our finding that the required skin testing surveillance of medical students is commonly inadequate makes it difficult to assess the accuracy of the estimated conversion rates. These rates reflect estimations based on yearly required testing, required testing done less frequently than yearly, and unscheduled voluntary testing. The calculated average conversion rates do not account for the variation in medical school sizes. Although we had no control over who actually answered the questionnaire and how familiar he or she was with the issue of purified protein derivative screening, we do know that the respondents' assessments of the likelihood of tuberculosis exposure correlated well with the CDC reported incidence of tuberculosis in the school's state. This suggests that the respondents were familiar with the issue of tuberculosis in their communities.

We conclude that the current state of tuberculin skin testing and monitoring in U.S. medical schools is inadequate. All medical schools should require tuberculin skin testing at matriculation into medical school and yearly thereafter and should have mechanisms in place to ensure compliance. Medical students working in locations with a high incidence of tuberculosis or in areas of hospitals or clinics where they are likely to encounter patients with active tuberculosis should be considered for more frequent testing (every 6 months). This is consistent with current published CDC recommendations [7]. Medical schools should consider taking responsibility for this as part of their ongoing prevention programs. Factors that may make such a program successful include education, removal of financial barriers, convenience for students, a designated responsible institutional committee or person, a visiting student-clerk policy, and a well-articulated policy for noncompliance with these requirements. We recommend that all U.S. medical schools review and update their tuberculin skin testing policies.