Evaluation of the Fully Automated Chemiluminescence Analyzer Liaison XL for the Performance of the QuantiFERON-TB Gold Plus Assay in an Area with a Low Incidence of Tuberculosis.

Diagnosis of latent tuberculosis infection (LTBI) is considered key in the control of tuberculosis. Interferon gamma (IFN-γ) release assays, such as the QuantiFERON-TB Gold Plus test (QFT-Plus), are now widely implemented for the in vitro diagnosis of LTBI. To date, the detection and quantification of IFN-γ has been mostly performed with semiautomated enzyme-linked immunosorbent assays (ELISAs), but several limitations currently exist. The study aims to evaluate the chemiluminescence immunoassay (CLIA) analyzer Liaison XL compared to ELISA for the performance of the QFT-Plus test. Between February and April 2020, 333 heparin blood samples from 323 adult patients were collected at a tertiary teaching hospital in Barcelona, Spain. Overall, the CLIA analyzer Liaison XL performed well for the detection of IFN-γ compared to the ELISA method, demonstrating substantial agreement (κ, 0.872) and great correlation between assays (r, >0.950). CLIA produced significantly higher values of IFN-γ IU per milliliter than the ELISA (P = 0.004 for the TB1 tube and P = 0.010 for the TB2 tube). Many discrepant cases (8/15, 53.3%) corresponded to indeterminate results with ELISA (NIL-corrected mitogen value of <0.5 IU/ml), which, when analyzed with the CLIA analyzer Liaison XL, reverted to interpretable results. In conclusion, this analysis suggests that CLIA presents a greater sensitivity for the identification of LTBI, especially among immunocompromised patients. Furthermore, the analytical variability reported between both ELISA and CLIA methods, especially around the standardized 0.35-IU/ml positivity threshold, suggests the need to refine the interpretative algorithm.

Preservation of Neisseria gonorrhoeae: should swabs be refrigerated or not?: Neisseria gonorrhoeae preservation.

Although molecular diagnosis has replaced culture as the reference technique in gonococcal infection, conventional culture is still performed. The aim was to compare the survival of Neisseria gonorrhoeae (NG) in transport swabs at room temperature (RT) and at 4°C. Fifty-four NG isolates were tested. A 1.5×108CFUmL-1 suspension was prepared for each strain, in which two swabs (Amies liquid medium with flocked swabs) were absorbed; one was preserved at RT and the other at 4°C. At 24 and 48h, 150µL of Amies medium were plated in Thayer Martin agar. The recovery percentage was significantly higher for the swabs kept at 4°C than for those kept at RT, both at 24h (94.4% vs. 16.7%), and at 48h (37% vs. 0%). This study clearly demonstrates the higher survival of NG when transport swabs are kept refrigerated. Modifying the guidelines could greatly improve the efficiency of microbiological diagnosis of the gonococcal infection.