Study: Drug-Resistant Tuberculosis Still a Global Threat

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A recent international study found alarmingly high levels drug-resistant strains of tuberculosis (TB) in a number of countries.

Researchers from the Centers for Disease Control and Prevention (CDC) report in the journal Lancet that rates of drug-resistant TB continue to climb in many parts of the world, despite heightened efforts to test and treat the disease. TB cases have increased in recent decades with the emergence of the AIDS epidemic; HIV-positive patients with weakened immune systems are more susceptible to infection with TB, and to spreading it to others.

The researchers reviewed 1,278 cases of multi-drug resistant (MDR) TB, which means the TB strains were resistant to first-line drug treatments and the patients were relying on second-line drugs in Estonia, Latvia, Peru, the Phillippines, Russia, South Africa, South Korea or Thailand. When the pathogen breaks free of these second-line treatments, it’s considered extensively-drug resistant (XDR), for which a very limited type of treatment currently exists.

To determine how widespread XDR TB is in each country, as well as to identify risk factors for transmission, lead researcher Tracy Dalton and her colleagues collected sputum (a mixture of saliva and mucus) samples from patients and tested them for drug susceptibility at both the local laboratories as well as at the CDC.

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Not surprisingly, the scientists found large differences in drug-resistant strains among the different countries. Overall, about 44% of patients had strains that were resistant to both first and second-line therapies, with rates ranging from 33% in Thailand to 62% in Latvia. XDR TB was found in 6.7% of the patients with 15.2% pevalence in South Korea and 11.3% in Russia, which the authors say is more than twice the World Health Organization’s (WHO) global estimate of 5.4%.

The researchers also found that the risk for XDR TB quadrupled in patients who were previously treated for the disease, also not surprising as the TB likely developed the ability to outsmart the  initial treatments with first and second line drugs.

The rise in drug-resistant TB of all types is worrying, since these cases are harder and costlier to treat. Countries with higher poverty rates tend to have a heavier burden of  drug-resistant strains due to lack of resources and access to the most up-to-date treatments. Which is why some health officials are embracing not just medical solutions but social policy strategies as well, urging governments to address unemployment, crime, alcohol abuse and smoking as part of their anti-TB efforts.

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In the U.S., the risk of contracting TB is very low. “There’s only about 100 cases of MDR TB a year, and there’s a median of 3 to 4 yearly cases of XDR TB in the U.S.,” says study author Dr. Peter Cegielski, a drug-resistant TB specialist at the CDC. “Our country’s affluence means we can address TB more vigorously than less affluent countries. The way we responded to TB has a lot to do with why it is declining in the U.S. and why drug resistance isn’t such a big problem.”

That said, Cegielski notes that drug-resistant TB spreads as easily as non-resistant TB and is a “threat to our ability to control TB in the U.S. and internationally.”

The country-specific data should help nations to develop more tailored strategies for testing their populations for TB and bringing patients in for proper treatment, before the strains have the opportunity to become resistant. “I think what this data points out are that there are substantial differences between countries and a one-size-fits all policy approach is not suitable for this public health problem,” says Cegielski. “The kind of data we present will enable those countries to address their own situation in a more targeted way.”

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