Relationship between Tuberculin Skin Test and COVID-19 Outcomes among Patients with COVID-19 in Zahedan, Iran

Ecological studies showed that countries with national Bacillus Calmette-Guerin (BCG) vaccination programs for tuberculosis prevention reported lower incidences of severe and fatal COVID-19 than countries without such programs. Several studies have demonstrated that the BCG vaccine can induce long-term trained Immunity in bone marrow progenitor cells. In this study, we tried to evaluate the relationship between tuberculin skin test results, BCG scar, and COVID-19 outcomes among patients with confirmed COVID-19.
This was a cross-sectional study. Cases included 160 patients with confirmed COVID-19 in Zahedan hospitals (southeast Iran) in 2020, selected by convenient sampling. PPD test was performed for all patients through the intradermal technique. Collected data included demographic information, underlying conditions, PPD test results, and COVID-19 outcome. Analysis was conducted utilizing ANOVA, χ2 test, and multivariate analysis (logistic regression).
The univariate analysis showed a positive relationship between older age, having underlying diseases, and positive tuberculin skin test results with the outcome of COVID-19. We also found a lower frequency of BCG scar among patients with death outcomes than recovered ones. In the multivariate analysis by logistic regression through the backward method, only age and underlying diseases remained predictors of death.
Tuberculin test results might be dependent on age and underlying conditions. Our study did not show relationship between BCG vaccine and mortality in COVID-19 patients. Further investigations in different settings are required to reveal the efficacy of the BCG vaccine in preventing this devastating disease.