Prevalence and factors associated with positive Tuberculin Skin Test (TST) among undergraduate medical students at Makerere University, College of Health Science Kampala-Uganda

Abstract

Tuberculosis (TB) is a major public health issue worldwide. Medical students in TB burdened countries are thought to be at unfavorably high risk of acquiring TB. This study therefore, was designed to determine the prevalence and factors associated with positive Tuberculin Skin Test (TST) among Makerere medical students.

Specific Objectives 1) To determine the prevalence of positive TST among Makerere University, undergraduate medical students. 2) To assess the effect of year of study on TST reactivity among Makerere University, undergraduate medical students. 3) To compare TST reactions of pre-clinical (year 1, 2 and 3) undergraduate medical students with that of clinical (year 4 and 5) undergraduate medical students.

Methodology This was a cross sectional TST survey with analytic component involving 288 sampled medical students enrolled for MB.ChB, BDS and BSN during the months of April-June 2009 from the first to the fifth year of their medical school.

Variables: Predictor variables included increasing age, male sex, clinical years, TB contact and Bacille Calmette Guérin (BCG) immunization status. Outcome was positive TST (induration ≥10mm if HIV negative and ≥5mm if HIV positive).

Analysis: The prevalence of positive TST was determined by dividing the number of subjects with positive TST with the total number of study subjects. Dichotomous and categorical variables were tested using chi-square test and continuous variables tested using t-tests. To assess predictors of a positive TST, uni-variable and multi-variable logistic regression analyses were conducted. An alpha level of <0.05 was considered for significant findings.

Results The prevalence of positive TST among medical students was 45.1% (95% C.I.39.3-50.0). There was a statistically significant linear relationship between year of study and TST positivity (p = 0.002, OR = 5.04). That is. 35.3%, 40.4%, 43.1%, 51.6% and 54.9% in year one to five respectively. Clinical compared to non clinical students has a higher prevalence of positive TST (53.0% vs 39.9%, p= 0.028, OR=1.7). Independent factors associated with positive TST were: male sex (p = 0.004, aOR=2.2); course dental surgery (p-value = 0.014, aOR=3.5) and contact with a case of TB, (p = 0.008, aOR=1.9).

Conclusion The likelihood of a positive TST among Makerere University Medical students increases in a linear pattern with increase in year of study. Although, history of contact was one of the explanation for a likelihood of a positive TST it was not possible to establish whether the increased risk in the higher years was due to nosocomial tuberculosis transmission as we did not evaluate whether contact with a TB case was in the hospital, household or elsewhere. In addition, lack of an appropriate control group made it difficult to conclude that medical students compared to students in other 5-year training programs at Makerere University are at an increased exposure to tuberculosis. Other factors that were predictive of a positive TST included male sex and being dental surgical student. We recommend that a similar study with an appropriate control group is conducted.