In a large international study published in the Lancet medical journal on Thursday, researchers found rates of both multi drug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) were higher than previously thought and were threatening global efforts to curb the spread of the disease.

"Most international recommendations for TB control have been developed for MDR-TB prevalence of up to around 5 percent. Yet now we face prevalence up to 10 times higher in some places, where almost half of the patients ... are transmitting MDR strains," Sven Hoffner of the Swedish Institute for Communicable Disease Control, said in a commentary on the study.

TB is already a worldwide pandemic that in 2010 infected 8.8 million people and killed 1.4 million of them.

Drug-resistant TB is more difficult and costly than normal TB to treat, and is more often fatal.

MDR-TB is resistant to at least two first-line drugs — isoniazid and rifampicin - while XDR-TB is resistant to those two drugs as well as a powerful antibiotic type called a fluoroquinolone and a second-line injectable antibiotic.

Treating even normal TB is a long process, with patients needing to take a cocktail of powerful antibiotics for six months. Many patients fail to correctly complete treatment, a factor which has fuelled a rise in the drug-resistant forms.

Researchers who studied rates of the disease in Estonia, Latvia, Peru, the Philippines, Russia, South Africa, South Korea, and Thailand found that almost 44 percent of cases of MDR TB were also resistant to at least one second-line drug.

SPREADS THROUGH AIR

Tracy Dalton from the United States Centers for Disease Control and Prevention, who led the study, said that so far, XDR-TB has been reported in 77 countries worldwide.

"As more individuals are diagnosed with, and treated for, drug-resistant TB, more resistance to second-line drugs is expected to emerge," she said.

The spread of these drug-resistant strains was "particularly worrisome" in areas with poor healthcare resources and limited access to effective drugs, she added.

TB is a bacterial infection that destroys patients' lung tissue, making them cough and sneeze and spread germs through the air. Experts say anyone with active TB can easily infect another 10 to 15 people a year.

The World Health Organisation (WHO) predicts that more than 2 million people will contract MDR TB by 2015.

A report by non-governmental organizations in March warned that $1.7 billion shortfall in global funds to fight TB over the next five years meant 3.4 million patients would go untreated and gains made against the disease will be reversed.

In their research, Dalton and colleagues found that rates of resistance varied widely between countries.

Overall, resistance to any second-line drug was detected in nearly 44 percent of patients, ranging from 33 percent in Thailand to 62 percent in Latvia.

In around a fifth of cases, they found resistance to at least one second-line injectable drug. This ranged from 2 percent in the Philippines to 47 percent in Latvia.

XDR-TB was found in 6.7 percent of patients overall. Rates in South Korea, at 15.2 percent, and Russia at 11.3 percent, were more than twice the WHO's global estimate of 5.4 percent at that time.

"These results show that XDR-TB is increasingly a cause for concern, especially in areas where prevalence of MDR-TB is high," said Hoffner.

(Editing by Alison Williams)

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