TB screening misses immigrants: Study

By Dr. Ananya Mandal, MDApr 28 2011

According to a latest study published in The Lancet, one in five new immigrants to the UK from the Indian subcontinent, and almost a third from sub-Saharan Africa, carried latent tuberculosis (TB).

In contrast to the current focus on symptomatic individuals, widened testing for latent TB would help to cut new cases, the researchers said. The UK currently screens migrants from countries with incidence over 40 cases per 100,000, but only checks for latent infection in a subset of individuals. This policy does not include those from the Indian subcontinent and so many latent cases are being missed, researchers said. TB cases in the UK rose by half to 9,040 between 1998 and 2009. Cases from overseas rose 98% in this time and now account for three quarters of all TB cases in the UK.

Ajit Lalvani from Imperial College London and his team looked at immigrants who should be screened to halt this rise. They assessed demographic and TB test result data from 2008-10 at three UK immigration centers. They found current UK policy has missed 70% of imported latent TB. Researchers calculated the cost effectiveness of screening various groups for latent TB. They concluded that the UK could identify 92% of all latent TB by testing everyone under 35 years immigrating from countries with TB rates of 150 per 100,000 or more. This would include immigrants from a number of Asian countries.

Professor Lalvani concluded, “Our findings provide the missing evidence-base for the new national strategy to expand immigrant screening.”

The data comes from a study accompanied by a cost effectiveness analysis. Between 2008 and 2010 the researchers analysed data collected from 1,229 immigrants to the UK, from immigration centres in Westminster, Leeds and Blackburn. All three centres were using a relatively new blood test called the interferon-gamma release-assay (IGRA) specifically to test for TB. Only people aged 35 or younger who had been screened for latent or hidden TB infection using this test were included in the analysis.  Of 1,229 immigrants, 245 (20%) tested positive in the IGRA tests, 982 (80%) tested negative and two people (0.2%) had indeterminate results.

The overall cost of extending latent screening would be around £20,000 per case of TB averted – “around £3000 more per case averted than the current [screening] programme”, says Lalvani. However, the group has not yet carried out a full cost analysis to confirm that extra screening is cheaper in the long run.