(AP) -- The World Health Organization says it doesn't have enough information to know if it is winning the fight against drug-resistant tuberculosis.
In a new report on the global status of drug-resistant TB based on data from 2008, the agency says almost half of all people with the disease are in China and India, with both countries reporting about 100,000 new cases each.
High rates of drug-resistant TB strains were also seen in eastern Europe and central Asia, with up to 60 percent of TB cases in some parts of Tajikistan and Uzbekistan being drug-resistant.
About 4 percent of all TB cases worldwide are thought to be non-responsive to the usual TB drugs. The agency estimated there were between 390,000 and 510,000 cases of drug-resistant TB in 2008, including about 150,000 people who were killed by the disease. But those numbers are based on modeling and come with a big margin of error.
The report is based on information from 38 countries worldwide, leaving a huge gap in the global TB picture.
"The country data reported to WHO make it impossible at this time to conclude whether the (drug-resistant TB) epidemic worldwide is growing or shrinking," the agency wrote in its report.
Drug-resistant TB usually arises when people are poorly treated or take substandard medicines. It takes longer to treat than regular TB and requires more expensive drugs, which also cause bad side effects like liver damage.
In recent years, WHO and other health authorities have warned the collision of TB with the AIDS virus could fuel simultaneous epidemics - and asked for more money to fight both. In its latest report, however, the agency acknowledged there is little proof of that.
Again citing missing data, the agency says "it has not been possible to conclude whether an overall association between (drug-resistant) TB and HIV epidemics exists."
In Estonia, Latvia and Moldova, WHO said people infected with both HIV and TB were more likely to develop drug-resistant TB. But there is no information from many countries across Africa where the most people with HIV live.
Some health experts wondered why WHO's report failed to mention in detail one of the main drivers of drug resistance: bad medicines.
"Many substandard drugs are fakes, but we are also concerned about legitimately manufactured copies - mainly from India and China - which are not made to exacting high standards," said Philip Stevens, a health policy expert at the London think-tank International Policy Network.
Stevens said the lack of global TB data was troubling. "WHO doesn't really have a clue as to the true extent of the problem," he said. "It's difficult then, to start promoting targets and goals when you don't know what baseline you are starting from."
WHO reported rates of drug-resistant TB were dropping in some parts of Russia with previously large outbreaks.
"It's good news that it can be controlled even in those difficult regions," said Ruth McNerney, a TB expert at London's School of Hygiene and Tropical Medicine, who was not connected to the report.
McNerney said that though progress was being made, authorities need more money to fight it, and more information about where the disease is striking. "We've got to find out where there are very serious problems, otherwise we won't know about it until it's too late."
Explore further: WHO warns of drug-resistant TB