London School of Hygiene & Tropical Medicine

As world TB day approaches on 24 March, The Lancet publishes a Seminar Online First that reports that, with increasing rates of drug-resistant TB, the progress being made for decades by world TB programmes is under threat. It also discusses how other risk factors, such as smoking and diabetes, are increasingly important in fuelling the global burden of TB.

The Seminar is by Dr Stephen Lawn, Reader in Infectious Diseases and Tropical Medicine, at LSHTM, who is based at the University of Cape Town, and South Africa Professor Alimuddin Zumla, University College London Medical School.

TB results in an estimated 1.7 million deaths each year and the worldwide number of new cases (more than 9 million) is higher than at any other time in history. Some 22 low-income and middle-income countries account for more than 80% of the active cases in the world. Due to the devastating effect of HIV on susceptibility to TB, sub-Saharan Africa has been disproportionately affected and accounts for four of every five cases of HIV-associated tuberculosis.

The authors say: "Increasing rates of drug-resistant TB in eastern Europe, Asia, and sub-Saharan Africa now threaten to undermine the gains made by worldwide tuberculosis control programmes."

As well as the well known risk factors for developing contracting TB and developing full blown disease (such as HIV which increases risk more than 20-fold, poverty and over-crowding), the Seminar lists other risk factors. The worldwide epidemic of diabetes and the very high rates of tobacco consumption in low- and middle-income countries are now believed to be increasingly important drivers of the TB epidemic. Diabetes increases risk three-fold and smoking increases risk two-fold. There are also many other risk factors, including cancers (both solid and blood based), vitamin D deficiency, alcoholism, indoor air pollution, long-term kidney failure, genetic variations, and use of corticosteroids and tumour necrosis factor (TNF) drugs to treat conditions such as rheumatoid arthritis. Studies in North America have shown that TNFs increase the risk of full-blown TB disease in infected patients by 50%, while for corticosteroids the risk is doubled.*

They conclude: "Absence of a cheap point of care diagnostic test, the long duration of treatment, lack of an effective vaccine, emergence of drug-resistant TB, and weak health systems in resource-poor developing countries are all factors that continue to hamper progress towards achieving control of TB worldwide. Despite this, there is growing momentum in basic and applied research activity that is starting to yield new diagnostic, treatment, and prevention methods, and now provide grounds for optimism. However, this growing scientific momentum must be matched by massive political and funder commitment to provide adequate funding to ensure that the aims of the WHO Global Plan to STOP TB 2006-15 are achieved."