The screening of immigrants for tuberculosis in Britain hasn’t been nearly as effective as health officials would like, especially since the testing fails to pick up on more than half of the cases, said government officials on Thursday.

In fact, Britain, which has been named the TB capital of Europe, is the only Western European nation with rising rates of the disease. As of now, border policies in Britain require that immigrants who come from countries with TB rates higher than 40 in 100,000 must have chest X-rays done to check for active TB in their bodies.

This usually means that most people from African countries have to be screened, but it excludes nations in Asia like Bangladesh, Pakistan and India.

TB is a bacterial infection in which only about 10% of cases lead to an activation of the disease that attacks the lungs and kills half of its victims. When immigrants arrive in Britain, most of them are only carriers of a latent form of TB, and it doesn’t activate itself until a few years after they’ve been living in Britain.

In data published in The Lancet Infectious Diseases journal, around 20% of people who emigrated from the Indian sub-continent and nearly 30% from sub-Saharan Africa were carriers of latent TB as discovered by British researchers. If this data is true, it means that the current TB screening method misses 70% of TB cases that cross the country’s border.