When John Humphrys on the Today programme recently expressed astonishment that roughly 70 per cent of all tuberculosis-carrying migrants slipped into the UK undetected, he added fuel to the immigration debate in these days of austerity and xenophobia.
As a third of the world's population carries tuberculosis bacteria (usually in its latent form), it is hardly surprising that visitors to the UK often have the germs. Most cases will remain latent. That is not to say there is not a problem - the incidence of TB has doubled here, in the past decade, to about 10,000 cases. Strains resistant to all known drugs have emerged, and TB must be considered an important part of the UK's health policy.
But blaming immigrants for the spread of disease is worrisome. Infectious outsiders have been ostracised since biblical times; Japan maintained leper colonies into the 1990s.
From Spanish flu to Mexican swine flu, we are quick to attribute disease to foreigners. In the early days of the Aids pandemic, US immigration systematically incarcerated HIV-infected Haitian refugees at Guantanamo Bay. Given that the Haitians had been infected by American sex tourists, this seems particularly repugnant, but it also shows what happens when the politics of race and paranoia enter public-health policy.