Longitudinal Evaluation of the QuantiFERON-TB Gold Plus Assay in Hospitalized COVID-19 Patients with a First Indeterminate Result: Resolution of Inflammation and Restoration T-lymphocyte Counts and Interferon-gamma Production

ABSTRACT

Background. Several studies reported an increased rate of indeterminate QuantiFERON-TB Gold Plus (QFT-P) assay results in patients with severe Coronavirus Disease (COVID)-19. Methods. Aim of the study was to longitudinally evaluate QFT-P responses in patients who survived COVID-19, with a previous indeterminate result. Results. We observed 223 patients with an indeterminate QFT-P assay among 949 patients hospitalized because of COVID-19 (23,5%) during 2020 and 2021. 36 patients among those with an indeterminate QFT-P assay were enrolled for reassessing the test. In 12 patients peripheral blood lymphocyte subsets were also reassessed. Considering disease severity, 30 were classified as severe and 6 as non-severe. Median age was 57,5 (interquartile range [IQR] 49,5-63,8), with a prevalence of male sex (M/F 24/12);median Charlson Comorbidity Index was 2 (IQR 1-3). The second QFT-P assay was performed after at least 1 month from the first assay (median time 7 months, IQR 5-12 months). All QFT-P assays gave a determined result: 2 positive (5.5%) and 34 negatives (94,4%). A statistically significant difference was observed after comparing the laboratory parameters at the time of the first and the second QFT-P assay the absolute counts of total lymphocyte, total CD3+, CD4+ and CD8+ T-lymphocytes were significantly increased (p< 0.001) while neutrophil absolute counts, neutrophil to lymphocyte (N/L) ratio, D-dimer,fibrinogen, ferritin, C-reactive protein (CRP) were significantly reduced (p< 0.0001). Concerning the QFT-P assay, interferon gamma (INF-gamma) production in the Mitogen-Nil, TB1-Nil and TB2-Nil conditions were significantly increased (p< 0.0001;p=0.0019;p=0.0205, respectively) (Table 1 and Figure 1). Conclusion. Once the acute phase of COVID-19 is resolved, inflammatory markers and peripheral blood leucocyte counts tend to normalize with an effective INF-gamma production after specific and nonspecific stimulation. All the 36 QFT-P showed a determinate result. Moreover, we observed 2 positive QFT-P assay, supporting the importance of retesting patients with indeterminate result to identify latent tuberculosis infection and monitor patients for possible reactivation because of the immunesuppression associated with COVID-19.