Over the next 20 years, cases of drug-resistant tuberculosis (TB) are set to rise in India, the Philippines, Russia, and South Africa – the four countries which already bear the highest burden.
A new study* published in The Lancet Infectious Diseases says the rise is likely to be the result of increased transmission of drug-resistant TB between people, rather than by strains acquiring resistance to anti-TB drugs.
Latest figures estimate that each year there are 10.4 million new cases of TB, leading to 1.8 million deaths globally. Nearly 40% of all drug-resistant cases occur in Russia, India, the Philippines, and South Africa – accounting for more than 230,000 cases of drug-resistant disease in 2015.
While better access to treatment programmes will reduce rates of drug-resistant TB in countries with a high burden, they will not eradicate the problem alone, and current efforts may not be enough to reverse the epidemic, the authors, from US Centers for Disease Control and Prevention, say.
Their study is based on a mathematical model that forecasts how TB is likely to progress in the four most-affected countries. It uses data from the World Health Organisation (WHO) and surveys estimating the number of drug-resistant TB cases to predict how many cases of multi drug-resistant and extensively drug-resistant TB would develop during 2000 and 2040. It also estimates how many of these would be a result of non-resistant strains acquiring resistance during treatment.
The model estimates that cases of both forms of drug-resistant disease will increase, suggesting that almost a third of tuberculosis cases in Russia (32.5%) would be multi drug-resistant by 2040, as well as 12.4% of tuberculosis cases in India, 8.9% in the Philippines, and 5.7% in South Africa. This compares to almost a quarter of cases (24.8%) in Russia, 7.9% in India, 6% in the Philippines, and 2.5% in South Africa in 2000.
In addition, almost one in 10 cases of multi-drug-resistant tuberculosis in each of the four countries were expected to be extensively drug-resistant by 2040 (9% in Russia and the Philippines, 8.9% in India, and 8.5% in South Africa), compared with around 1% in 2000 (1.3% in Russia, 1.6% in the Philippines, 0.9% in India, and 0.4% in South Africa).
The study predicts that fewer cases of drug-resistant tuberculosis will be caused by strains acquiring resistance – reducing from around 30% of cases of multi drug-resistant tuberculosis in 2000 to 20-25% in 2040, and 80% of cases of extensively drug-resistant disease in 2000, to 50% in 2040.
As a result, the authors say research into additional control measures will be needed to prevent drug-resistant tuberculosis spreading between people. To reduce the burden of drug-resistant disease, the researchers recommend that treatment be coupled with ways to prevent spread of the disease, such as early detection, reducing the number of patients who do not complete treatment, and providing tailored treatment depending on which drugs the strain is susceptible to.
“We cannot focus solely on curing people with tuberculosis or drug-resistant tuberculosis if we want to halt the epidemic. Even if we prevent new drug-resistant infections, there are enough current cases to keep the epidemic going, and drug-resistant tuberculosis will continue to be an increasingly dangerous threat so long as resistant strains spread through the air from one person to another,” says one of the authors, Dr Aditya Sharma.
“We need to dramatically step up efforts to break the cycle of transmission – while also maintaining work to rapidly find and treat all people with tuberculosis. We must strengthen infection control measures, focus on households, health centres, and communities to prevent tuberculosis spreading from person to person, and develop more effective diagnostic tests to rapidly and accurately detect drug resistance,” she added.