Medical students at risk: Prevalence and incidence of tuberculin skin test conversion

Introduction: One third of the world population is affected by latent tuberculosis, with 9.4 million new cases; medical students have 2 to 50 times the probability of acquiring the infection. Objectives: Establish the baseline prevalence of positive tuberculin skin test (TST) at the beginning of medical studies and determine the incidence and variables associated with TST conversion in medical students. Materials and Methods: Secondary analysis of a historical cohort (2007-2010) of medical students in a private Peruvian university. The TST conversion was evaluated. A binomial regression analysis was applied for each associated variable. Results: 707 medical students were included, of whom 219 (31%) were male. The basal prevalence of reactive TST was 14.4%. Significant associations were found with the year of university entry of 2007-08 (p = 0.007) and a history of tuberculosis (p = 0.02). With a total of 822 person-years, the incidence of conversion was 2.92 cases per 100 person-years (CI95%: 1.96-4.36). The TST conversion was associated with the year of university entry (RR = 2,55; IC95%: 1,06-6,30) and a body mass index ≥ 25 kg/m² (RR = 0,16; IC95%: 0,01-0,97). No association was detected with gender, tobacco or alcohol use. Conclusions: There is evidence of a high basal prevalence of latent tuberculosis infection in medical students. The incidence rate is within expected values and high in comparison with the general population. People with BMI ≥ 25 kg/m² have protection against a latent infection. In medical students, more attention should be paid to biosecurity.