Emergence of extensively drug-resistant tuberculosis holds unsettling consequences

By Ava Torjani

A recent study found that a rare form of multi-drug resistant tuberculosis (MDR TB), called extensively drug-resistant tuberculosis (XDR TB), has been spreading across regions of South Africa and currently has no effective treatment for or prevention against it. Although in much smaller numbers, cases of XDR TB have also been reported in countries including the U.S., Russia, and Brazil.

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Tuberculosis (TB) is an airborne disease characterized by coughing – occasionally with blood – fatigue, fever, and weight loss. Although it usually affects the lungs, it can also cause issues with the liver, kidney, and heart, which leads to detrimental outcomes including meningitis and heart failure. It is one of the top ten causes of death globally, and is the number one killer of HIV-positive patients. Typical treatment constitutes a six-month course of antimicrobial drugs with extensive supervision to ensure prescription adherence. The Bacille Calmette-Guérin (BCG) vaccine is used to prevent severe types of TB in children but is an ineffective prevention measure for adults. As of 2013, there have been 450,000 reported cases of active TB, showing an increase of 400% over the last fifteen years.

While MDR TB is resistant to first-line drugs like isoniazid and rifampin, it can be effectively treated with second-line drugs, albeit with slightly worse side effects and a longer, two-year treatment span. Unfortunately, XDR TB includes resistance to both first-line and at least one second-line drug, making it substantially more difficult to identify new, equally effective treatments. In fact, the current treatment for XDR TB has more side effects, is costlier, and can only be applied to 30-50% of those who get XDR TB. With a combination of treatment difficulty and the fact that 95% of cases occur in low- or middle- income countries, XDR TB has an alarming fatality rate of 50 to 80%.

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Causes for the emergence of this strain of TB include lack of proper adherence to medical prescription (dosage and time), re-development of the disease after having already taken medication for it, and proximity with someone who has it, given its airborne nature. If you are exposed to someone with XDR TB, it is recommended you get a TB skin test or a QuantiFERON®-TB Gold test at a medical center as soon as possible. However, testing highlights yet another concerning matter on this strain of TB: to distinguish between drug-susceptible and drug-resistant TB, extra tests need to be conducted that can take 6 to 16 weeks to get conclusive results. Dr. Michael Gardam, a doctor managing the TB clinic at Toronto’s Universal Health Network, effectively sums up all issues associated with XDR TB in the following statement: “We all know that tuberculosis is something that spreads between people, but it just hasn’t been as big a focus with XDR and MDR [multi-drug resistant] TB because there’ve been so many treatment failures that have caused [new] cases.”

All in all, though primarily concentrated in South Africa, the infectious nature of XDR TB highlights the need for effective treatment of and prevention strategies against it. The Centers for Disease Control and Prevention (CDC) proposed several suggestions, including improving accessibility to TB drugs and healthcare providers, establishing more efficient diagnostic tests, and boosting preparedness for outbreaks. However, if no action is taken, XDR TB could soon become similar to the recent unexpected, contagious outbreaks of Ebola or H1N1 flu. Therefore, the emergence of this deadly strain of TB is a warning not only to those living in susceptible regions of South Africa, but globally, since drug resistance is a very common phenomenon.

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