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When “Manuel”, a 62-year old-New Yorker who had rarely sought medical help, went into hospital after complaining of coughing and chest pains this spring, he received a double shock. Not only was he diagnosed with tuberculosis, requiring isolation and six months of treatment, but diabetes as well.
His experience reflects the growing realisation of the links between the two diseases. Those with diabetes are at far higher risk of contracting TB, present more difficulties when being treated for it, and may contribute to the infection’s spread.
That the two conditions are connection is not a new discovery. In 1,000BC, the Persian philosopher and physician Avicenna discovered that phthisis (TB) caused complications in people with diabetes. Dr Anthony Harries, who long worked in Malawi, says: “As a physician, I have known for many years anecdotally that people with TB often also have diabetes.” But it was only in the past decade that researchers began to examine the phenomenon in such detail. They concluded that people with diabetes are up to three times as likely to contract TB. The multiple is higher still for younger people.
Today, about 15 per cent of adults with TB have diabetes – or more than 1m people globally. A study in 2012 suggested the proportion was as high as 39 per cent in Texas and 40-45 per cent in the South Pacific. Rising trends in obesity and diabetes risk such proportions increasing still further in the years ahead.
In the past, diabetes was often considered largely a disease of rich countries as their lifestyles became more sedentary and changing diets boosted obesity; while TB was seen primarily as a disease of the poor. However, rapid urbanisation and industrialisation have contributed to a sharp convergence in lifestyles and diseases alike, with experts increasingly talking about a “double burden” in developing countries.
The greatest global toll of diabetes is in China and India, which also have the highest numbers of TB sufferers. A 2012 study in Kerala, India, found 44 per cent of those with TB also had diabetes.
By weakening the human immune system, diabetes makes people more susceptible to tuberculosis. Diabetics who have already been treated for TB have a higher chance of redeveloping the infection. And with an estimated 3m people a year contracting TB but not diagnosed, there is a substantial danger that diabetes patients attending clinics will catch TB from others.
It is less clear that TB makes people more susceptible to diabetes. But recent work suggests those with TB may prove both more difficult to diagnose with diabetes and more difficult to treat. Some tuberculosis drugs may interact differently in the body. When TB medicines are given to diabetics, they may require alternative treatments and higher doses over longer periods – in turn adding to the risks of toxicity and reducing the chance of a cure.
While the fight against TB remains relatively poorly funded by governments and donors, it has received far more attention since the start of the millennium than other diseases in many poor and middle-income countries.
There has been some progress in providing “integrated” care, linking TB and HIV, as the leading global infectious disease killers.
Now the debate is shifting to firming up links with diabetes, as part of an effort to integrate the treatment of various non-communicable diseases in low and middle-income countries. The problem is that treatment for diabetes, as with other chronic conditions, is poorly funded, requiring many patients to pay out of their own pocket.
Diabetic specialists have also proved reluctant to diagnose TB. But attitudes are changing. When hundreds of researchers gathered in Barcelona last month for the annual meeting of the International Union Against Tuberculosis and Lung Disease, diabetes came up repeatedly. As a report presented at the meeting warned: “If we fail to act [against diabetes], the consequences could prove catastrophic for healthcare systems in areas that are impacted.”
Efforts by the Union, the World Diabetes Foundation and the World Health Organisation are bringing progress. The Indian and Chinese governments have run pilots for “bidirectional” screening and support between the two diseases, and India has changed its national policy as a result.
More research and clinical guidelines, and practical experience, are required. Vouchers and support groups may be necessary to motivate people to attend clinics regularly. National screening, and registers to identify and monitor patients could also be important.
But the surge in obesity risks slowing or even reversing the progress made in reducing the global burden of TB. As Dr Harries concedes: “With the lifestyle changes and cheap food of the urban poor, it’s probably going to get worse.”