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Blood test hope in battle against soaring TB levels

Scientists in Glasgow are spearheading research into new blood tests for tuberculosis in a bid to halt rocketing levels of the disease.

Cases of TB in Scotland have shot up 25% in the past 10 years, with the vast majority of new diagnoses occurring among immigrants from at-risk countries including India and Pakistan, and parts of Africa.

These patients tend to have arrived in the UK as carriers of a dormant, or latent, form of the disease which displays no symptoms and cannot be picked up by X-rays, but which is sub-sequently reactivated to become full-blown TB. If left untreated, it kills more than 50% of sufferers.

There were 455 new cases of TB last year, according to Health Protection Scotland.

Existing screening techniques have mixed results. Airport chest X-rays of immigrants arriving from countries with high-TB levels can only detect active TB, and even then only picks up 70% of cases.

Until now, the only method of identifying latent TB has been a skin test developed more than 100 years ago in which a potential carrier's arm is scratched and checked for an immune response. This is roughly as accurate as the new blood tests, but more difficult to perform and slower to produce a result. It has never been used routinely in the UK as a screening tool.

Sarah Whitehead, laboratory lead for TB in Glasgow, is now leading an evaluation of two new TB blood tests at the Southern General Hospital.

Ms Whitehead, who is also an adviser on the UK TB Task Force, said: "Roughly 10% of immigrants with latent tuberculosis will progress to having active TB in their lifetime and obviously it's a bad thing to be infecting other people in Scotland.

"So what we really want to do in this screening programme is pick them up and give them drug treatment which will get rid of or suppress their latent TB so they don't actually go on to develop TB.

"We've got some new laboratory tests now which we're looking at. We're currently evaluating these tests, so over the next couple of months we will see how good they are, and how good they would be to use in Glasgow."

One of the tests, QuantiFERON-TB Gold, manufactured by German-based technology firm QIAGEN, is already in use in Germany, France and Ireland, where it has dramatically reduced the incidence of TB.

It is hoped the results of the blood test evaluation could be used in a pilot public health scheme mooted for next summer. Although NHS Greater Glasgow and Clyde has made no definite decision on whether to run the pilot, discussions are under way to invite at-risk immigrant groups, via their GPs, to attend blood test screenings at Glasgow Royal Infirmary.

If they test positive for latent TB they could be prescribed drugs to treat it, substantially reducing their risk of developing TB from 10% to 1%.

Although routine vaccination of infants with the BCG jab, and to an even greater extent improved nutritional and living standards, have helped drive down cases of TB over the past 100 years, the native population continued to account for the majority of new TB cases until relatively recently.

However, while cases among immigrants now make up the bulk of new diagnoses this is not believed to pose a significant public health threat, with little evidence of it spreading into the native population.

Dr Onn Min Kon, consultant respiratory physician and member of the UK TB Task Force, added: "We urgently need to stem the tide of rising TB cases in the UK. This is not a problem that can be tackled by healthcare professionals alone – it needs to be a joint effort with policy and society. We look forward to an informative discussion about how best to tackle the influx of TB infection."

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