On the heels of the news of totally drug-resistant (TDR) TB being identified in India — and disavowed, unfortunately, by the Indian government — the World Health Organization has released an update on the background situation of drug-resistant TB around the world.
The news is not good. Drug-resistant TB is at the highest rates ever recorded.
A quick vocabulary briefing. There is an array of drugs for TB: two very long-standing ones, and three newer ones, that are collectively called “first-line” drugs; and a category of less-effective second-choice drugs, collectively called “second-line.” (Nothing to do with New Orleans funerals.) The distinction is important because, while any TB treatment takes a very long time, second-line treatment takes much longer: 2 years, as opposed to 6 months or so for first-line drugs.
Think of how often you’ve missed or forgotten a dose when you’re taking a 10-day antibiotic prescription. Now imagine how hard it is to stick to a drug regimen when you’re taking antibiotics multiple times a day for two years.
If that sounds difficult, then you’ve just glimpsed the challenges of treating TB — and that’s without counting the lack of cheap, accurate diagnostics that show which drugs TB strains are resistant to; the failure of good primary care to prescribe drugs properly and monitor how they are being taken; the persistence of counterfeit drugs in the market; and the (real) drugs’ unpleasant side effects.
By agreed-up international definitions, MDR (multi-drug resistant) TB is unaffected by the first-line drugs, and XDR (extensively drug-resistant) TB is not susceptible to any of the first-line drugs and some of the second-line ones also. In addition, doctors who have seen TDR cases (which was originally dubbed XXDR for “extremely” drug-resistant) say those strains are resistant to every drug they have available locally — but the WHO has objected to that terminology, pointing out that “everything available locally” is not necessarily the same thing as “every drug available anywhere.”
This new WHO report is primarily concerned with MDR and XDR. It says that MDR-TB has now been identified in 80 countries; XDR TB has been found in 77. The meat of the report, though, is in these numbers; overall:
- 19.8 percent of MDR patients were previously treated for TB.
- 3.4 percent were never treated for TB before.
- 9.4 percent of all resistant cases are XDR.
Here’s what is going on there. MDR in a previously treated patient represents a failure of treatment: They did not take their drugs, were not able to get drugs, or got counterfeit drugs; their TB strain was not knocked out, but persisted and strengthened. But MDR in a first-time patient represents transmission of MDR-TB from someone who developed it. Those patients never get a chance to try the easier drugs. And XDR in any patient, whether newly acquired or bred via poor treatment, is an emergency.
Within the report, some of the numbers are staggering. The proportion of previously treated cases that become MDR is 51 percent in Belarus, 60 percent in Lithuania, 65 percent in Moldova. In China, 26 percent of previously treated TB cases are now MDR. In Estonia, 19 percent of all MDR cases are now XDR. Meanwhile, India and Russia, two of the biggest contributors to resistant TB because of their size and the state of their healthcare systems, report resistant cases only on a local level, not nationally. And most of Africa lacks the infrastructure to measure resistant TB at all.
There’s a lot to be said about innovations in the fight against TB — when I wrote about TDR a few weeks ago, I heard from a number of NGOs and nonprofits — but that will have to wait for another post. Meanwhile, though, here are the maps from the WHO Bulletin, showing where MDR-TB is occurring.
Cite: Zignol M, van Gemert W, Falzon D et al. Surveillance of anti-tuberculosis drug resistance in the world: an updated analysis 2007-2010. Bull World Health Organ 2012;90:111–119D. doi:10.2471/BLT.11.092585
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