Multidrug-resistant tuberculosis is an increasing threat, according to investigators with the U.S. Centers for Disease Control and Prevention.
In a study that focused on Russia, India, South Africa and the Philippines — four countries with a so-called "high burden" of multidrug-resistant TB — researchers estimated that within the next 25 years, the proportion of TB cases that don't respond to one or more antibiotics will increase significantly in those areas.
Russia leads the pack, researchers reported. Their mathematical model predicts that one-third of TB cases in Russia will be multidrug or extensively-drug resistant by 2040.
India is next, with more than 12.4 percent of the cases expected to be resistant to treatment, followed by almost 9 percent in the Philippines and 5.7 percent of cases in South Africa.
These four nations accounted for more than 230,000 new cases of difficult-to-treat tuberculosis in 2015 — nearly 40 percent of drug-resistant cases worldwide, according to the CDC investigators.
The latest findings were published in the journal The Lancet Infectious Diseases.
Peter Cegielski, team leader for Prevention, Care and Treatment of Tuberculosis at the CDC's Global Tuberculosis Branch, said infected individuals can develop drug-resistant strains by not taking their medications properly. This is known as acquired TB. However, Cegielski said the primary driver now is person-to-person transmission, with drug-resistant bacteria spreading through the air.
"The TB germs, if you cough or sneeze, the TB germs can remain suspended in the air for hours, so anybody else in the vicinity can inhale one and become infected," he said.
Cegielski said airborne transmission of TB is not regularly targeted as part of prevention efforts, but it should be. He said tuberculosis was brought under control in the West in large part by infected people covering their nose and mouth when they sneezed or coughed.
In addition to encouraging people to follow that example, Cegielski said public health officials need to step up containment efforts to keep drug-resistant cases of TB from getting out of control.
"So that means expanding the diagnostic capabilities of laboratories in low- and middle-income countries; expanding access to rapid diagnosis and effective treatment to make sure that everybody who has TB is treated properly in the first place," he said.
Worldwide, there are 10.4 million new cases of TB each year, resulting in nearly 2 million deaths. The bacteria, says Cegielski, kills more people than any other germ on the planet.
Cegielski warns that drug-resistant TB is going to become increasingly more common, resulting in many more deaths, unless more money is spent on prevention and treatment efforts.