UK tuberculosis screening for new immigrants is missing most imported cases of latent infection. The study, published Online First in The Lancet Infectious Diseases, also suggests that a screening programme capable of identifying the vast majority of immigrants with latent tuberculosis could be implemented cost-effectively, substantially reducing future cases of active tuberculosis. The study was jointly funded by the UK Medical Research Council and the Wellcome Trust.
Current UK policy requires that all immigrants from countries with a tuberculosis incidence higher than 40 per 100,000 have a chest X-ray on arrival to check for active tuberculosis. However, whereas very few immigrants have active tuberculosis on arrival, many are carriers of latent tuberculosis, which often progresses to infectious active tuberculosis within a few years of arrival in the UK. Although national guidelines have advocated screening specific groups for latent tuberculosis, it has been largely restricted to immigrants from sub-Saharan Africa, and until now its true benefit and cost-effectiveness were unknown.
In this study, Ajit Lalvani from Imperial College London, London, UK and colleagues set out to define which immigrant populations should be screened to stop the continued rise in UK tuberculosis rates (which almost doubled between 1998 and 2009) and whether this can be done cost-effectively.
The researchers analysed demographic and test result data from 2008 to 2010 at three immigrant screening centres in the UK using a highly specific blood test for detecting latent tuberculosis—the interferon-gamma release assays (IGRA).
The analysis showed that 20% of recent immigrants from the Indian Subcontinent and almost 30% from sub-Saharan Africa are carriers of latent tuberculosis. The current national screening policy, which excludes immigrants from the Indian subcontinent (who account for half of all active tuberculosis cases in the UK), has been missing 70% of imported latent tuberculosis.
The researchers also modelled how cost-effective it would be to decrease the screening threshold for the incidence of tuberculosis in the country of origin. They predict that testing all immigrants aged 35 years and younger from countries with tuberculosis rates of 150 cases per 100 000 or more would identify 92% of infected immigrants and would be cost-effective, costing little more than what is spent on screening now, relative to the number of active tuberculosis cases prevented.
Professor Lalvani concludes: "UK national guidance for which groups to screen has hitherto missed most immigrants with latent infection. We've shown that by changing the threshold for screening, and including immigrants from the Indian Subcontinent, we could pick up 92% of imported latent tuberculosis. By treating people at that early stage, we can prevent them from developing a serious illness and becoming infectious. Crucially, this wider screening could substantially reduce tuberculosis incidence while remaining cost-effective. Our findings provide the missing evidence-base for the new national strategy to expand immigrant screening."*
Professor Ajit Lalvani, Imperial College London, London, UK. T) +44 (0) 7767 700 873 E) a.lalvani@imperial.ac.uk
Notes to Editors: *Quote direct from author not verbatim from Article
Please note: an accompanying Comment will appear with this article in the print edition of Lancet Infectious Diseases; this is not yet available. However the author of this Comment is available on contact details below: Dr Anna Mandalakas, Case Western Reserve University, Cleveland, Ohio, USA. E) anna.mandalakas@case.edu Skype) +1 216 220 0706 Please note Dr Mandalakas is currently in South Africa
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