Is the course of COVID-19 associated with tuberculin skin test diameter? A retrospective study

The pathogenesis of coronavirus disease 2019 (COVID-19) is still not fully understood. As severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) has a similar pathogenetic pathway to Mycobacterium tuberculosis, it has been reported that there may be a relationship between Bacille Calmette-Guerin (BCG) vaccination rate and COVID-19 severity. This study investigated the relationship between tuberculin skin test (TST) induration diameter and the clinical course of COVID-19. Of 1963 adult patients who underwent TST, 76 patients with SARS-COV-2 infection confirmed by RT-PCR analysis of respiratory tract samples were included in the study. Relationships between COVID-19 clinical severity and TST positivity, induration size, and other clinical parameters were analyzed. Of the 76 patients, TST results were negative for 53 patients (69.7%) and positive for 23 patients (30.3%). COVID-19 severity was mild in 47 patients (61.8%), moderate in 22 patients (28.9%), and severe in seven patients (9.3%). All TST-positive patients had mild disease. Patients with mild disease had a significantly higher TST positivity rate (p < 0.001) and larger induration diameter (p < 0.001). The area under the receiver operating characteristic (ROC) curve of TST induration size for the differentiation of mild with moderate and severe disease was 0.768 (p < 0.001). The maximum Youden J index value was 0.522 at an induration diameter of 6.5 mm, which had a sensitivity of 66.0% and specificity of 86.2%. COVID-19 patients with positive TST showed a significantly higher rate of mild disease than those with negative TST. TST positivity is favorably associated with the course of COVID-19.