Cases of drug-resistant tuberculosis are forecasted to increase in the four high-burden countries (India, the Philippines, Russia, and South Africa) between 2000 and 2040, with the upturn likely to be a result of increased transmission of drug-resistant tuberculosis between people, rather than by strains acquiring resistance to anti-tuberculosis drugs, according to a study published in The Lancet Infectious Diseases.
While better access to treatment programs will reduce rates of drug-resistant tuberculosis in countries with a high burden, they will not eradicate the problem alone, and current efforts may not be enough to reverse the epidemic.
As a result, 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 is coupled with ways to prevent the 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.
Bacteria of Tuberculosis
“This study uses a complex model bringing together the best available data from multiple sources in four countries hit hard by the drug-resistant tuberculosis epidemic. Our findings show that drug-resistant tuberculosis cases in these countries are expected to rise over the next two decades and that fewer cases over time will be caused by acquired drug resistance during tuberculosis treatment. These findings suggest that person-to-person transmission will become the engine that drives drug-resistant tuberculosis in these countries,” says Dr. Aditya Sharma, US Centers for Disease Control and Prevention, USA.
Latest figures estimate that each year there are 10.4 million new cases of tuberculosis, leading to 1.8 million deaths globally. Nearly 40% of all drug-resistant tuberculosis cases occur in Russia, India, the Philippines, and South Africa – accounting for more than 230000 cases of the drug-resistant disease in 2015.
Tuberculosis is a bacterial disease that can be treated with a combination of antibiotic drugs. However, as a result of use and misuse of antibiotics (such as using the wrong drug, or not completing the full course of treatment) bacteria can develop drug resistance (known as acquired drug resistance).
There are two forms of drug-resistant tuberculosis important to public health – multidrug-resistant tuberculosis is resistant to more than one of the first-line drugs for the disease, whereas extensively drug-resistant tuberculosis is additionally resistant to fluoroquinolones and at least one of the second-line injectable tuberculosis drugs.
Treating extensively drug-resistant tuberculosis takes up to 2 years with toxic drugs, including daily injections that can have severe long-term side effects (eg, hearing loss, psychosis). Around 40% of people diagnosed with multidrug-resistant tuberculosis die of the disease, compared with 60% of those with extensively drug-resistant tuberculosis.
The study is based on a mathematical model that forecasts how tuberculosis is likely to progress in the four most affected countries. It uses data from WHO and surveys estimating the number of drug-resistant tuberculosis cases to predict how many cases of multidrug-resistant and extensively drug-resistant tuberculosis 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 multidrug-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 ten 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 multidrug-resistant tuberculosis in 2000 to 20-25% in 2040, and 80% of cases of the extensively drug-resistant disease in 2000, to 50% in 2040.