London: A new study conducted by Imperial College London on Thursday revealed that immigrants arriving from India, Pakistan and Bangladesh have signs of latent Tuberculosis as British airports are failing to detect these people at the check post.

Professor Ajit Lalvani, Director of the Tuberculosis Research Unit at Imperial College, who led the study, said, "Our findings indicate that immigrants arriving in the UK from countries with high burdens of TB have a high prevalence of latent tuberculosis infection, which is strongly associated with tuberculosis incidence in their country of origin."

He added, "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 per cent of imported latent TB."

The study has been published in The Lancet Infectious Diseases.

The investigators found that a fifth of recent immigrants from the Indian subcontinent and almost 30 per cent from Sub-Saharan Africa are carriers of latent TB and that national screening policy, which does not include immigrants from the Indian subcontinent, has been missing 70 per cent of imported latent TB.

The researchers also assessed how cost-effective it would be to lower the threshold so that people from more countries are screened.

They found that including immigrants from the Indian subcontinent for screening would detect 90 per cent of latent TB cases, and would cost little more than what is spent on screening now, relative to the number of active TB cases prevented.

The current UK policy requires that all immigrants from countries with a TB incidence higher than 40 in 100,000 per year have a chest X-ray on arrival to check for active TB, although very few immigrants have active TB on arrival.

However, a substantial proportion of immigrants are carriers of latent TB which though initially silent and non-infectious, often progresses to full-blown, infectious active TB within a few years of arrival in the UK.

The incidence of TB has risen dramatically in Britain over the last decade, increasing by almost 50 per cent between 1998 and 2009.

Much of this increase has been driven by a 98 per cent increase in cases among people who move to the country from overseas, the study found.

Foreign-born individuals account for nearly three quarters of the country's TB cases, and have a 20 times higher incidence of TB than people born in the UK.