27 April 2011 by Jessica Hamzelou
London may owe its reputation as the tuberculosis capital of Europe to the UK's TB screening programme. A new study suggests the current policy for screening immigrants from countries with a known TB problem misses 71 per cent of those who carry the disease but do not display symptoms. A policy change that would cost little more could bring that number down to 8 per cent.
British policy is to X-ray people arriving from countries known to have 40 or more cases of active TB for every 100,000 people. However, X-rays are effective at identifying active infections only: individuals who don't display symptoms of disease remain undetected. "Their X-ray scans are normal," says Ajit Lalvani at Imperial College London.
Latent TB can take anywhere from a few weeks to a lifetime to develop into an active form of the disease, but around 5 per cent of carriers will develop full-blown TB within a few years, says Lalvani.
Immigrants arriving in the UK from countries with 500 or more cases of active TB per 100,000 people face a more stringent test that will detect latent TB. It involves exposing a blood sample to TB antigens. If a person's immune system has been exposed to such an antigen before, the blood's T-cells will respond by releasing a protein known as interferon gamma; otherwise, the T-cells will do nothing. People with both active and latent forms of the disease can be identified in this way.
Lalvani and his colleagues studied three busy TB screening centres in London, Leeds and Blackburn – regions with high levels of TB in the immigrant population – between 2008 and 2010. Their analysis suggested that the current rules for TB screening were missing 71 per cent of cases of latent TB, which may prove costly to treat if they develop into an active form of the disease.
£3000 per case
To find a cost-effective alternative, the group analysed the estimated costs and benefits associated with lowering the latent TB screening threshold in order to screen more immigrants. They found that by using latent-TB screening for people from countries with TB rates above 150 per 100,000 – rather than 500 per 100,000 – they would be able to catch 92 per cent of latent TB cases.
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. He suggests that extending latent screening this way would actually save money, because it may cost a lot more to deal with cases of full-blown TB arising from latent infections: as well as treating the patient, everyone that they have been in contact with must be screened to make sure they have not become infected, which may be expensive.
However, the group has not yet carried out a full cost analysis to confirm that extra screening is cheaper in the long run.
Journal reference: The Lancet, DOI: 10.1016/s1473-3099(11)70069-x
http://www.newscientist.com/article/dn20424-british-screening-misses-most-incoming-latent-tb.html
London may owe its reputation as the tuberculosis capital of Europe to the UK's TB screening programme. A new study suggests the current policy for screening immigrants from countries with a known TB problem misses 71 per cent of those who carry the disease but do not display symptoms. A policy change that would cost little more could bring that number down to 8 per cent.
British policy is to X-ray people arriving from countries known to have 40 or more cases of active TB for every 100,000 people. However, X-rays are effective at identifying active infections only: individuals who don't display symptoms of disease remain undetected. "Their X-ray scans are normal," says Ajit Lalvani at Imperial College London.
Latent TB can take anywhere from a few weeks to a lifetime to develop into an active form of the disease, but around 5 per cent of carriers will develop full-blown TB within a few years, says Lalvani.
Immigrants arriving in the UK from countries with 500 or more cases of active TB per 100,000 people face a more stringent test that will detect latent TB. It involves exposing a blood sample to TB antigens. If a person's immune system has been exposed to such an antigen before, the blood's T-cells will respond by releasing a protein known as interferon gamma; otherwise, the T-cells will do nothing. People with both active and latent forms of the disease can be identified in this way.
Lalvani and his colleagues studied three busy TB screening centres in London, Leeds and Blackburn – regions with high levels of TB in the immigrant population – between 2008 and 2010. Their analysis suggested that the current rules for TB screening were missing 71 per cent of cases of latent TB, which may prove costly to treat if they develop into an active form of the disease.
£3000 per case
To find a cost-effective alternative, the group analysed the estimated costs and benefits associated with lowering the latent TB screening threshold in order to screen more immigrants. They found that by using latent-TB screening for people from countries with TB rates above 150 per 100,000 – rather than 500 per 100,000 – they would be able to catch 92 per cent of latent TB cases.
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. He suggests that extending latent screening this way would actually save money, because it may cost a lot more to deal with cases of full-blown TB arising from latent infections: as well as treating the patient, everyone that they have been in contact with must be screened to make sure they have not become infected, which may be expensive.
However, the group has not yet carried out a full cost analysis to confirm that extra screening is cheaper in the long run.
Journal reference: The Lancet, DOI: 10.1016/s1473-3099(11)70069-x
http://www.newscientist.com/article/dn20424-british-screening-misses-most-incoming-latent-tb.html
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