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

Abstract

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.

An Effective Health System Approach to End TB: Implementing the Double X Strategy in Vietnam

“…Early implementation in 2020–2021 ACF campaigns showed low TST positivity for household contacts compared with previous research results in Vietnam, 37 prompting the USAID Support to End TB project to explore issues with TST as previously described. 35 Among household contacts aged 5 years and older in 2020, QFT positivity (38.6%) had higher agreement with TST ≥5 mm (37.4%) than TST ≥10 mm (13.1%); QFT results were not discordant with TST ≥5 mm but were discordant with TST ≥10 mm. Older age groups (>30 years), but not sex, increased odds for positive QFT and TST ≥5 mm.…”

“…During 2X ACF campaigns, household contacts of individuals with drug-susceptible pulmonary TB disease were evaluated for TB infection with tuberculin skin tests (TST) ( Figure 2 ), which has been previously described. 35 A subset of individuals (2,887 [8.8%]) received both QuantiFERON TB-Gold Plus (QFT) (Qiagen, Hilden, Germany) and TST for quality assurance. Simultaneous evaluation for TB disease and TB infection capitalized on the “1-stop shop” ACF campaigns to screen for both TB disease and infection in a single encounter.…”