LOS ANGELES -- Extensively drug-resistant tuberculosis -- or XDR-TB -- is appearing in more countries and is estimated to have caused 16,000 deaths in 2005.
LOS ANGELES, Feb. 26 -- Extensively drug-resistant tuberculosis -- or XDR-TB -- is appearing in more countries and is estimated to have caused 16,000 deaths in 2005.
"While that number appears small now, it is almost certain to continue to rise," according to Paul Nunn, M.D., of the World Health Organization.
The 28 countries that have reported cases of XDR-TB are up from 17 last March, Dr. Nunn told a plenary session here at the annual Conference on Retroviruses and Opportunistic Infections.
The numbers are almost certainly an underestimate, he said, because in most African countries -- areas where TB is endemic -- facilities to test TB strains are lacking.
So-called multidrug resistant TB (MDR-TB) is defined by the WHO as tuberculosis that is resistant to the two first-line drugs, isoniazid (Nydrazid) and rifampin (Rifadin).
XDR-TB arises when a multidrug resistant strain also becomes resistant to any fluoroquinolone, and at least one of three injectable second-line drugs -- capreomycin (Capastat), kanamycin (Kantrex), and amikacin (Amikin).
"Most African countries don't have a laboratory capable of testing for resistance to the first-line drugs, let alone the second-line drugs," Dr. Nunn said.
On the positive side, he said, the rising XDR-TB numbers probably aren't because the disease is spreading in an epidemic fashion, but because MDR-TB is being inappropriately treated in similar ways in many different countries.
It is "not so much a spread," he said, as the emergence of "similar patterns of resistance."
Dr. Nunn added he expects to see more XDR-TB in China, India, and the Russian Federation, which among them have two-thirds of the world's cases of MDR-TB.
The continued rise of XDR-TB is "hugely problematic," especially for countries where HIV is also raging, Dr. Nunn said in an interview.
He said controlling XDR-TB will need about million this year and every year for the next decade, in order to improve surveillance, treatment, and prevention.
While XDR-TB has been known for several years, its effects were dramatically illustrated in a presentation at the Toronto International AIDS Conference last July, when researchers outlined an outbreak among HIV-positive people in South Africa.
In that outbreak, 52 of 53 patients died within two weeks of diagnosis, researchers said.
South Africa -- one of the few African countries able to track XDR-TB -- has now seen the disease appear in all of its nine provinces and 40 of its hospitals, according to Karin Weyer, Ph.D., director of TB research for the South African Medical Research Council.
Dr. Meyer told the retrovirus meeting that there are an estimated 600 cases of XDR-TB in South Africa a year -- and especially among people with HIV -- they are almost uniformly deadly.
"More than 85% of deaths take place in people who are HIV-positive," Dr. Weyer told reporters earlier.
But perhaps more alarming is that HIV-negative people stay on treatment but do not get well -- owing to the extensive drug resistance -- making them reservoirs of disease, she said.
The "prolonged survival of these patients in itself poses a public health risk," Dr. Weyer said, "because of their prolonged period of infectiousness."
Although XDR-TB usually arises because of mismanaged treatment for MDR-TB, Dr. Weyer said, community transmission is possible and has been seen.
But the main transmission risk is to health-care workers, she said, especially in South Africa, where many are also HIV-positive.