The fight against tuberculosis by world health programmes is under threat from rising rates of drug-resistant TB, new findings suggest.

Additional risk factors including smoking and diabetes are also “increasingly important” in fuelling TB across the globe, a seminar published in the medical journal The Lancet found.

Authors Alimuddin Zumla, of University College London Medical School, and Stephen Lawn, professors at the University of Cape Town, said TB resulted in an estimated 1.7 million deaths each year, with the worldwide number of new cases – exceeding nine million – higher than at any other time in history.

They recorded that 22 low-income and middle-income countries accounted for more than 80 per cent of the active cases in the world. Sub-Saharan Africa had been disproportionately affected and accounted for four of every five cases of HIV-associated tuberculosis, due to the effect of HIV on susceptibility to TB.