The Doctor's World
Rise of a Deadly TB Reveals a Global System in Crisis
LOS ANGELES — The spread of a particularly virulent form of tuberculosis in South Africa illustrates a breakdown in the global program that is supposed to keep the disease, one of the world’s deadliest, under control.
The program was intended to detect tuberculosis cases, make sure patients were taking their antibiotics, test patients for resistance to those drugs and monitor the spread of the disease.
But international tuberculosis experts say the system is in deep trouble for an array of reasons: misuse of antibiotics; other bad medical practices, like failing to segregate high-risk patients in hospitals and clinics; and cuts in government spending for such basics as adequate supplies of drugs and laboratories to do the testing.
Such factors have led to the rise of drug-resistant tuberculosis bacteria, a menace the world has only begun to appreciate.
Mycobacterium tuberculosis, the microbe that causes the disease, was discovered 125 years ago this month. Today, the bacteria infect 8.8 million people a year and cause 1.6 million deaths. They are spread in tiny droplets when patients cough.
Tuberculosis is curable, as long as the bacteria are susceptible to antibiotics. It becomes deadlier when it attacks people who are also infected with H.I.V., the AIDS virus. And when the tuberculosis bacteria become extremely drug-resistant, the death rate soars.
That was the case in Tugela Ferry, a rural town in KwaZulu-Natal province in South Africa, when an outbreak of extremely drug-resistant tuberculosis — XDR-TB for short — killed 52 of its 53 victims, all of whom were also infected with H.I.V. The outbreak was detected in 2005, but it did not receive international attention until it was reported at the international AIDS meeting in Toronto last August.
The World Health Organization calls the extremely drug-resistant form “a grave public health threat” because of its potential explosiveness among the millions of H.I.V.-infected people in poor countries. It seems to be a lesser threat among people who do not have H.I.V., though it could be dangerous to the millions with weakened immune systems from treatment for cancer and other diseases.
XDR-TB is defined as tuberculosis that is resistant to the two most important antituberculosis drugs (isoniazid and rifampin), along with two other drugs: a member of the fluoroquinolone class and at least one of three others (capreomycin, kanamycin and amikacin).
A step lower on the resistance scale is a form of the disease called MDR-TB, for multidrug-resistant tuberculosis. An outbreak of that form struck in New York City in the early 1990s, and cost at least $1 billion in emergency measures to control and manage tuberculosis patients.
Experts say the tuberculosis outbreak in South Africa is the deadliest one that they can recall.
Although South African officials, who have known about the outbreak for a year, promised a prompt and full investigation, even experts there acknowledge that efforts are lagging.
“Unfortunately, we do not know much more than a year ago” mainly because “a systematic survey in each of the provinces has not yet started,” Dr. Karin Weyer of the South African Medical Research Council told the Conference on Retroviruses and Opportunistic Infections here recently.
Dr. Weyer said in an interview that she had hoped that rapid surveys and screening tests would have been completed by now to show better the geographic extent of the disease.
Using statistics from recent years, Dr. Weyer said her team estimated that 6,000 new cases of multidrug-resistant tuberculosis occurred in South Africa each year and that the rate of treatment failure was about 10 percent. Assuming that most failures were due to the extremely drug-resistant form, a conservative estimate is 600 cases of XDR-TB in her country each year, Dr. Weyer said.
In data that her team examined, about 85 percent of patients infected with XDR-TB and H.I.V. died, she said. The fatality rate in H.I.V.-negative patients seemed lower, but could not be determined until they complete long-term therapy.
What is known is that the deadly XDR-TB strain has been found in more than 40 hospitals in all nine provinces of South Africa, she said.
The rest of sub-Saharan Africa is at risk, she went on, because “control of airborne infection is either totally inadequate or even absent” in virtually all of those countries.
The outbreak is not limited to Africa. Dr. Paul Nunn, a tuberculosis expert at the World Health Organization, told the meeting here that one or more cases of XDR-TB had been found in at least 28 countries. Extrapolating from data about the multidrug-resistant form of tuberculosis, Dr. Nunn estimated that two-thirds of the XDR-TB cases were from China, India and Russia...
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