Extensively Drug Resistant TB Levels Alarming

Tuberculosis that is resistant to first-line and second-line drugs is becoming more prevalent, an international team of experts reported in The Lancet today. They described levels of extensively drug-resistant TB as “alarming”. 43.7% of TB (tuberculosis) cases in eight countries were found to be resistant to at least one second-line drug.

In a linked Comment in the same journal, Sven Hoffner, from the Swedish Institute for Communicable Disease Control wrote “Most international recommendations for TB control have been developed for MDR TB prevalence of up to around 5%. Yet now we face prevalence up to ten times higher in some places, where almost half of the patients with infectious disease are transmitting MDR strains.”

Drug resistant TB is much harder and significantly more expensive to treat – it is usually more deadly too. The authors are particularly concerned about extensively resistant TB in areas of the world where resources are scarce.

As drug resistant tuberculosis becomes more widespread, so will resistance to second-line drugs. A report published in the New England Journal of Medicine in July 2012, informed that 10% of all TB cases in China are drug-resistant.

According to lead author, Tracy Dalton, from the US CDC (Centers for Disease Control and Prevention), extensively drug-resistant TB has been reported in 77 countries around the world. Nobody is certain how widespread it is.

Dalton and team gathered population-based data from various public and private sources to determine how widespread extensively drug-resistant TB is in Thailand, South Korea, South Africa, Russia, the Philippines, Peru, Latvia and Estonia. Their study, called PETTS (Preserving Effective TB Treatment Study), also set out to identify which risk factors are associated with TB infection.

11 first-line and second-line antituberculosis medications were tested at the CDC laboratories in the USA on isolates from 1,278 adults from the eight countries.

They found that:

• 44% of the isolates were resistant to any second-line drug. Resistance ranged from 62% in Latvia to 33% in Thailand.
• In one fifth of all cases, there was resistance to at least one second line intravenous drug (injection). Resistance ranged from 47% in Latvia to 2% in the Philippines.
• Nearly 13% of all cases were resistant to a fluoroquinolone. Resistance ranged from 32% in South Korea to 7% in the Philippines
• 6.7% of all patients had extensively drug-resistant TB. Prevalence in Russia at 11.3% and South Korea at 15.2% was over double the 5.4% global figure estimated by the World Health Organization (WHO)
• Previously-treated patients were four times as likely to become infected with extensively drug-resistant TB
• Patients who had received second-line drug treatment in the past were the most likely to later on become infected with TB that was resistant to second-line drugs

The researchers also found that alcohol abuse, having been in prison, unemployment and smoking were linked to resistance to second-line injectable drugs. Dalton said that “social factors should be taken into account in the management of TB”.

Sven Hoffner added:

“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.”