Application of T-SPOT.TB in the Diagnosis of Cutaneous Mycobacterium marinum Infections and Evaluation of Treatment Efficacy

This study evaluated the diagnostic value and therapeutic efficacy assessment potential of the interferon-γ release assay T-SPOT.TB in cutaneous Mycobacterium marinum infections. A total of 145 patients diagnosed at the Institute of Dermatology, Chinese Academy of Medical Sciences (2020-2024), excluding tuberculosis cases, were retrospectively analysed. Clinical data including demographics, underlying diseases, pathology, microbiological culture, molecular identification, T-SPOT.TB results, treatment regimens, and outcomes were collected. T-SPOT.TB results before treatment, and at 3 and 6 months post-treatment, were compared to assess its diagnostic and monitoring utility. The baseline T-SPOT.TB positivity rate was 71% (95% CI: 63.2-77.8%). Among 17 patients retested at 3 months, positivity was 64.7% (p = 0.125), with median spot-forming cells (SFCs) significantly decreasing from 20.0 (IQR 8.5-41.0) to 8.0 (IQR 2.5-28.0) (p = 0.0007). Among 27 patients retested at 6 months, positivity was 59.3% (p = 0.344), with median SFCs decreasing from 12.0 (IQR 5.0-30.0) to 8.0 (IQR 3.0-13.0) (p = 0.0006). No significant difference in positivity rates was observed between 3 and 6 months post-treatment. The T-SPOT.TB assay shows significant diagnostic value for cutaneous M. marinum infections and facilitates early diagnosis. Declining SFC counts post-treatment provide useful reference for evaluating therapeutic response.