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Thorax 68:230-239 doi:10.1136/thoraxjnl-2011-201542
  • Tuberculosis
  • Original article

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

  1. Onn Min Kon3
  1. 1Department of Respiratory Medicine, Tuberculosis Research Unit, National Heart and Lung Institute, Imperial College London, London, UK
  2. 2Department of Infectious Disease Epidemiology, MRC Centre for Outbreak Analysis and Modelling, Imperial College London, London, UK
  3. 3Tuberculosis Service, Chest and Allergy Clinic, St Mary's Hospital, Imperial College Healthcare NHS Trust, London, UK
  4. 4Department of Clinical Immunology, St Mary's Hospital, Imperial College Healthcare NHS Trust, London, UK
  5. 5Formerly Director of Public Health/Medical Director, Westminster Primary Care Trust, London, UK
  6. 6Modelling and Economics Unit, Health Protection Agency, London, UK
  1. Correspondence to Dr Onn Min Kon, Consultant Respiratory Physician, Chest and Allergy Clinic, St Mary's Hospital, Imperial College Healthcare NHS Trust, Praed Street, London W2 1NY, UK; onn.kon{at}imperial.nhs.uk
  1. Contributors The initial study was designed and set up by OMK and MG with input by MP and AL. MB and JS undertook the immigrant screening and entered the data into the databases. SS was in charge of setting up and analysing the IGRA results. MP analysed the data and designed the economic model with input from OMK, AL and PJW. MP drafted the manuscript with input from all other authors. All authors approved the final version to be published. OMK is the guarantor.

  • Received 3 January 2012
  • Accepted 16 May 2012
  • Published Online First 12 June 2012

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.

Footnotes

  • Independence The authors' work was independent of the funders, who had only a minimal role in the study design but no role in the analysis of data, writing of the manuscript or decision to submit for publication.

  • Funding This study was undertaken at St Mary's Hospital, Imperial College Healthcare NHS Trust which is supported by the NIHR Biomedical Research Centre funding scheme. Westminster Primary Care Trust provided funding for the project. MP is funded by a Medical Research Council Capacity Building Studentship. PJW thanks the Medical Research Council for Centre funding. AL is a Wellcome Senior Research Fellow in Clinical Science and NIHR Senior Investigator.

  • Competing interests AL is inventor for patents underpinning T-cell-based diagnosis. The ESAT-6/CFP-10 ELISpot was commercialised by an Oxford University spin-out company (Oxford Immunotec, Abingdon, UK) in which Oxford University and Professor Lalvani have a minority share of equity. MP, SS, MB, JS, MG, PJW and OMK have no conflict of interest.

  • Ethics approval No patient-specific data or personal identifiers were used in the preparation of this report which was an analysis of routine data collected as part of service evaluation and therefore ethical approval was not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement Full numerical results of the scenarios described here are available from the corresponding author on request.

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