Tuberculosis may be rare in the United States, but elsewhere around the world it’s a different story. Drug-resistant strains of TB are increasing in a number of countries, thanks to the disease becoming resilient to second-line treatments.
The trend is becoming worrisome, enough so that researchers from the Centers for Disease Control and Prevention undertook a study of resistance rates and causes among 1,278 patients with multi drug-resistant TB in eight countries: Estonia, Latvia, Peru, the Philippines, Russia, South Africa, South Korea and Thailand. Samples were tested for resistance to 11 first- and second-line drugs. The findings were published this week in The Lancet.
Overall rates were alarming: almost 44 percent of all patients were resistant to at least one second-line drug, and 20 percent were resistant to at least one second-line injectable drug. Results varied widely by country. About a third of Thai patients and 62 percent of Latvian patients showed resistance.
Among all patients, 6.7 percent were considered extensively drug-resistant, or XDR, a step up from multi drug-resistant, or MDR. MDR patients are resistant to at least two first-line drugs, isoniazid and rifampicin, while XDR patients are resistant to isoniazid, rifampicin, a fluoroquinolone (an antibiotic) and a second-line injectable drug. It follows that XDR TB patients have fewer options for treatment.
There was another reason to be concerned about drug resistance rates: The study found that the risk of becoming extensively drug-resistant was more than four times higher in people who had been treated before. Having been treated before with second-line drugs was the biggest risk factor for resistance.
Researchers also discovered that biology wasn’t the only factor related to being resistant to second-line injectable drugs. Social issues such as alcohol abuse, being imprisoned, smoking, and being unemployed were also linked.
“Drug-resistant TB is more difficult and costly to treat, and more often fatal,” lead author Tracy Dalton of the CDC said in a news release. “Internationally, it is particularly worrisome in areas with fewer resources and less access to effective therapies. As more individuals are diagnosed with, and treated for, drug-resistant TB, more resistance to second-line drugs is expected to emerge.”
In an accompanying editorial, Sven Hoffner of the Swedish Institute for Communicable Disease Control, said, “These results show that XDR TB is increasingly a cause for concern, especially in areas where prevalence of MDR TB is high. Nevertheless, information remains insufficient to give a clear view of the worldwide distribution and true magnitude of XDR TB. Updated information on MDR TB and investigation of the trends are urgently needed...especially since the true scale of the burden of MDR and XDR tuberculosis might be underestimated and seem to be rapidly increasing.”
In the U.S., the CDC reports that there were 11,182 TB cases in the 2010—that’s 3.6 cases per 100,000 people. Compare that to Sub-Saharan Africa, where the World Health Organization says there were more than 270 cases per 100,000 people in 2010.
“Our country’s affluence means we can address TB more vigorously than less affluent countries,” study co-author Dr. Peter Cegielski of the CDC told Time. “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.”
Do you think these high resistance rates pose a threat to global health? Let us know in the comments.