Community-based evaluation of immigrant tuberculosis screening using interferon γ release assays and tuberculin skin testing: observational study and economic analysis

Abstract

Background UK tuberculosis (TB) notifications are rising due to disease in the immigrant population. National screening guidelines have been revised but cost-effectiveness analyses are hampered by the lack of data on the comparative performance of tuberculin skin tests (TSTs) and interferon γ release assays (IGRAs) in immigrants. Methods Three-way evaluation of TSTs and two IGRAs (QuantiFERON Gold in-tube (QFN-GIT) and T-SPOT.TB) in immigrants aged ≥16 years to quantify test positivity, concordance and factors associated with positivity. Yields were computed at different incidence thresholds and the relative cost-effectiveness of screening was estimated using different latent TB infection (LTBI) screening modalities at varying incidence thresholds with or without port-of-arrival chest x-ray (CXR). Results 231 immigrants were included; median age 29 (IQR 24–37). TSTs were accepted by 80.9%, read in 93.5% and 30.3% were positive – QFN-GIT and T-SPOT.TB positive in 16.6% and 22.5% respectively. Positive TSTs, QFN-GIT and T-SPOT.TB were independently associated with increasing TB incidence in immigrants’ countries of origin (p=0.007, 0.007, 0.037 respectively). Implementing current guidance (threshold 40/100 000 per year) would identify 98–100% of LTBIs (depending on test) but entail testing 97–99% of the cohort; screening at 150/100 000 per year would identify 49–71% of LTBIs but only entail screening half the cohort. The two most cost-effective screening strategies were no port-of-entry chest radiography and screen with single-step QFN-GIT at 250/100 000 per year (incremental cost-effectiveness ratio (ICER)) £21 565.3/case averted); and no port-of-entry CXR and screen with single-step QFN-GIT at 150/100 000 per year (averted additional 7.8 TB cases; ICER £31 867.1/case averted). Conclusions UK immigrant screening could cost-effectively and safely eliminate mandatory CXR on arrival by emphasising systematic screening for LTBI with single-step IGRA. Intermediate incidence thresholds balance the need to identify as many imported LTBIs as possible against limited service capacity.

A systematic review of economic models used to assess the cost-effectiveness of strategies for identifying latent tuberculosis in high-risk groups

“…Four [9][10][11][12] economic evaluations were conducted in Japan, three [13][14][15] in the USA and two [3,4] in the UK, and one [16] in South Africa.…”

“…In the UK, current guidelines recommend the use of IGRAs and/or TST for the diagnosis of LTBI in high risk populations which include children, people who are immunocompromised or at risk of immunosuppression and people from countries with a high incidence of TB. [3] The health economic modelling which underpin these recommendations are based on 'what-if' analyses/scenarios rather than empirical screening evidence [4] and this offers little insight on which diagnostic strategy is the most cost-effective.…”

Gamma Interferon Assays Used in the Diagnosis of Tuberculosis

“…Thus, there may be false-positive results from both tests. However, several publications show strong evidence that the use of the TB IGRA was cost-effective, especially when testing high-risk individuals, such as health care workers, immigrants from countries where tuberculosis is endemic, and individuals with close contact with infected individuals (household contacts) (27,28).…”

‘Pre-entry screening for tuberculosis’ commentary: authors' response

“…[3][4][5] These cost-effective analyses should take account of the previously discussed points plus the length of stay of migrants. They should be informed by a better understanding of tuberculosis transmission dynamics in different social and ethnic groups, considering both foreign-born and UK-born individuals and consider the costs of diagnosing and treating active tuberculosis.…”