• Tuberculosis

The number of cases of active tuberculosis (TB) continues to rise in the UK and in many other parts of the world.1 2 In analysing the reasons behind this rise, it needs to be kept in mind that only a small proportion of those who become infected with TB will progress to become ill with active TB disease in the weeks and months after infection. They do, however, remain at risk of reactivation of their latent TB infection in the years (and indeed decades) to come. Clearly, a co-existing medical condition which impairs the immune response to the TB bacterium might increase the likelihood of direct progression to active disease shortly after infection, or increase the likelihood of latent TB infection in later life. Co-infection with HIV is a striking example; the relative risk of developing TB in HIV-positive individuals compared with HIV-negative individuals (the incidence rate ratio) is between about 20 and 35.2

In this issue of Thorax, Walker and Unwin (see page 578) consider the impact on numbers of TB cases in England of another increasingly common condition—namely, diabetes mellitus.3 A link has long been suggested, the authors pointing out that combined clinics for those with diabetes and TB were being held more …