Tuberculin skin testing and QuantiFERON™-TB Gold Plus positivity among household contacts in Vietnam

SETTING

TB infection (TBI) is diagnosed using the technique-dependent tuberculin skin test (TST) or costly, more accurate interferon-gamma release assays. The TST (⩾10 mm) threshold was indicated by previous research among household contacts in Vietnam, but routine implementation with a different tuberculin reagent showed unexpectedly low TST positivity.

OBJECTIVE

TST (⩾5 mm and ⩾10 mm) results were compared to QuantiFERON™-TB Gold Plus (QFT) results in household contacts during community campaigns in 2020 and 2021.

DESIGN

This was a cross-sectional multi-center implementation study.

RESULTS

Among 1,330 household contacts in 2020, we found a TBI prevalence of 38.6% (QFT), similar to TST ⩾5 mm (37.4%) and higher than TST ⩾10 mm (13.1%). QFT+/TST+ was higher for TST ⩾5 mm (20.7%) than TST ⩾10 mm (9.4%). QFT was not discordant with TST ⩾5 mm (McNemar's test = 0.6, P = 0.5) but was discordant with TST ⩾10 mm (McNemar's test = 263.9, P < 0.01). Older age and Southern region increased odds for positive TST ⩾5 mm and QFT with weaker associations for TST ⩾10 mm. Agreement and discordance were similar in 2021 for 1,158 household contacts.

CONCLUSION

Tuberculin reagents affect TST positivity rates. High TB burden countries should monitor reliability of TBI diagnosis, including tuberculin potency, cold chain, and TST technique to optimize eligibility for TB preventive treatment.

Immunocytochemical characterization of viruses and antigenic macromolecules in viral vaccines

Gold immunolabeling combined with negative staining (GINS) provides a valuable immunocytochemical approach that allows a direct ultrastructural definition of all viral vaccine constituents that share common antigenic features with pathogenic viral particles. These results have implications for the development of viral vaccines since it has been demonstrated that incomplete viral particles such as natural empty capsides and Rotavirus-like particles lacking the infective genome are potential candidates for the production of neutralizing antibodies. Furthermore comparative results of the application of GINS to either inactivated vaccines or unfixed samples provide direct evidence that even after inactivation specific antigenic sites are still available for gold immunolabeling.