Community-based evaluation of immigrant tuberculosis screening using interferon γ release assays and tuberculin skin testing: observational study and economic analysis.
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.
Department of Respiratory Medicine, Tuberculosis Research Unit, National Heart and Lung Institute, Imperial College London, London, UK.
Manish
M
Pareek
Marion
M
Bond
Jennifer
J
Shorey
Suranjith
S
Seneviratne
Margaret
M
Guy
Peter
P
White
Ajit
A
Lalvani
Onn Min
OM
Kon
D000293:Adolescent; D000328:Adult; D001208:Asia / Q000208:ethnology; D003362:Cost-Benefit Analysis; D004641:Emigration and Immigration; D005260:Female; D006801:Humans; D015994:Incidence; D059425:Interferon-gamma Release Tests / Q000191:economics; D055985:Latent Tuberculosis / Q000175:diagnosis* / Q000191:economics / Q000208:ethnology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011446:Prospective Studies; D013902:Radiography, Thoracic / Q000191:economics; D014374:Tuberculin Test / Q000191:economics; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000191:economics / Q000208:ethnology*; D006113:United Kingdom / Q000453:epidemiology; D055815:Young Adult