The problem of multidrug-resistant tuberculosis may be even more severe than previously thought, experts warn.
Patients must complete a full course of drugs to cure TB
A survey of 79 countries by the World Health Organization published in the Lancet found TB drug resistance in virtually every one.
Particularly high levels of resistance were seen in regions of the former Soviet Union and parts of China.
About a third of the world's population is infected with the TB bug, with 8.9 million developing TB each year.
In 2004, the respiratory disease caused 1.7 million deaths worldwide.
Kazakhstan: 14.2% of new cases
Tomsk, Russia: 13.7%
Liaoning province, China: 10.4%
Henan province, China: 7.8%
Anti-microbial drugs have proved very effective at treating TB.
But experts believe their misuse has given the bacteria too much chance to evolve new defences which render the drugs less effective.
The biggest problem is patients failing to complete a full course of the drugs.
Even though symptoms might have disappeared, small amounts of the bacteria may remain, and are capable of mutating.
Multidrug-resistant TB strains are those that are resistant to at least the two most potent drugs, isoniazid and rifampicin.
More dangerous strains
Scientists have recently reported an even more worrying from - extensive drug-resistant TB (XDR-TB) - which has been found among people with HIV in South Africa.
The latest study was carried out for the Global Project on Anti-Tuberculosis Drug Resistance Surveillance, which was set up in 1994.
From their analysis, the WHO team estimated there were 424,000 cases of multidrug-resistant TB world-wide in 2004.
China, India and Russia accounted for half of these cases.
The researchers believe about 1% of new cases of TB are caused by multidrug-resistant strains. However, in eight countries, including Kazakhstan and Latvia, the figure was above 6.5%.
Three countries - Andorra, Iceland and Malta - had no cases of resistance to first-line drugs, while in the United States, Hong Kong and Cuba, the cases of MDR TB showed a decline.
Lead researcher Dr Mario Raviglione said: "The findings of the Global Project emphasise the importance of implementing sound tuberculosis control activities to prevent further creation of MDR tuberculosis, and the necessity of mainstreaming high-quality treatment for MDR tuberculosis into routine tuberculosis control programmes.
"Otherwise XDR-TB is bound to keep emerging as a fatal variant of TB, especially in high HIV prevalence settings."
Cases of tuberculosis (TB) in England, Wales and Northern Ireland rose by 10.8% in 2005, figures show.
Lack of funds
Professor Peter Davies, of the organisation TB Alert, said TB - and in particular multidrug resistant strains of the disease - was a bigger problem than people had expected it to be.
He said around US$500m had been committed globally to the search for new drugs - but this was only around half the amount a commercial pharmaceutical company spent on developing one product.
"We are simply not getting the funding for new drugs and vaccines that is required," he said.
"New drugs are being discovered, but there is no money to put them through randomised clinical trials.
"We have known this is a problem for 20 years, but we have not been serious about controlling TB."