A dangerous form of drug-resistant tuberculosis has reached its highest levels ever, accounting for at least 5% of all new TB cases worldwide and 15% to 22% of new cases in parts of the former Soviet Union and China, the World Health Organization said Tuesday.
The WHO report, the first new survey of TB incidence in four years, estimates that there are nearly 500,000 new cases of multidrug-resistant TB, commonly known as MDR TB -- about 5% of the 9 million total new cases of TB each year.
The highest rate was recorded in Baku, the capital of Azerbaijan, where 22.3% of all new cases were MDR. Rates of 14.8% or higher were also found in Moldova, the Donetsk province of Ukraine, the Tomsk province of Russia and in Tashkent, the capital of Uzbekistan.
MDR TB was also found in a high proportion of cases in the Inner Mongolia and Heilongjiang regions of China.
In contrast, the highest rate reported in the 2004 survey was 14.2% in Kazakhstan.
Experts attributed the high incidence in these regions to poverty, crowding, alcoholism and stress from the dismantling of the Soviet Union.
Surprisingly low rates of drug-resistant strains were found throughout most of southern Africa, which has the highest rates of TB in the world -- although most countries in the region were unable to report data because of the lack of sophisticated laboratories to test for the variants.
Dr. Mario Raviglione, director of WHO's Stop TB Department, attributed the low incidence to the overall lack of treatment in southern Africa. If the majority of people are not getting antibiotics, he noted, the TB bacteria will not develop resistance to them.
"But with the more widespread use of rifampicin and other drugs [in recent years], the situation is going to go more quickly out of control because of the presence of HIV," which leaves victims much more susceptible to TB, he said. HIV is the virus that causes AIDS.
Tuberculosis is an infection of the lungs characterized by fever, weight loss, night sweats and coughing up of blood.
The disease is spread primarily through microscopic droplets released when an infected person coughs, sneezes or speaks.
The MDR variety of the disease is resistant to two first-line antibiotics, isoniazid and rifampicin. Treatment can take up to two years, compared with six months for conventional TB. The drugs used are more toxic and 100 times as costly.
An even more serious form, known as extensively drug-resistant TB, commonly called XDR TB, is resistant to both of these antibiotics and to fluoroquinolones and any of the injectable antibiotics, such as kanamycin or capreomycin. Treatment may require surgical removal of part of the lungs, and some strains are virtually untreatable.
The WHO survey found that XDR TB has been detected in 45 countries.
Drug-resistant strains of TB develop when patients do not complete their course of treatment, allowing mutated versions of the bacterium to emerge. These new strains can then be passed from person to person, just like the older ones.
There were 111 cases of MDR TB and three cases of XDR TB in the U.S. in 2006, according to the national Centers for Disease Control and Prevention.
Only a few years ago, scientists dismissed drug-resistant TB as a major threat. Most thought it could occur only in HIV-positive patients whose immune systems were suppressed, and they also believed that the development of resistance lowered the virulence of the bacterium and impaired its ability to spread.
Now, Raviglione said, these ideas have been proved wrong.
The problem can be solved with increased surveillance and better access to antibiotics, researchers said. Raviglione pointed to Estonia and Latvia, two former Soviet republics that were hot spots for drug-resistant TB a decade ago, with rates of 10% to 12%. With better detection and treatment, he said, "the number of cases is coming down quite quickly, 5% to 10% per year, and the MDR percentage has stabilized. The number of cases is half what it was 10 years ago."
Money is the major problem in improving control. WHO estimates that $4.8 billion is needed this year for overall control of TB in low- and middle-income countries, with about $1 billion of that directed toward drug-resistant strains.
But only half that amount is available, the report says.
"The threat created by TB drug resistance demands that we fill these gaps," said Dr. Marcos Espinal, executive secretary of the Stop TB Partnership, a network of more than 500 international organizations dedicated to eliminating TB.