New test for TB speeds detection

Faster results could help stop spread, JHU researcher says

October 12, 2006|By Jonathan Bor | Jonathan Bor,Sun reporter

Detecting tuberculosis and preventing its spread could become easier with a new test that produces results in days rather than weeks and quickly indicates whether patients carry drug-resistant strains, researchers report today.

Doctors who studied tuberculosis in Peru said the test could become a major tool in taming a disease that preys mostly on people in developing nations but is also becoming a threat in Europe. TB kills close to 2 million people worldwide each year.

"It's taken a long time, but our mission is to basically take this test now that it's been evaluated and implement it in developing countries," Dr. Robert H. Gilman, a professor at the Johns Hopkins Bloomberg School of Public Health, said yesterday.

"Speed is not just for the patient, but it's important from a public health standpoint as well," added Gilman, senior author of the study appearing in today's New England Journal of Medicine.

Tuberculosis is an ancient yet curable scourge that affects mainly the lungs. The disease is particularly dangerous to people with HIV infection because their immune systems are too weak to mount an attack. Early symptoms include a cough with thick, often bloody mucous, a rapid heartbeat and a swollen neck.

The test that's widely used in poor nations takes three to four weeks to indicate whether a patient is infected with the TB bacteria. A follow-up test takes just as long to signal whether the person carries a strain that's resistant to drugs.

In the meantime, the patient may have been given ineffective drugs while spreading the hard-to-treat strain. The delay can be deadly, not just for the patient but for others sharing crowded living spaces, work environments, buses and trains.

In an accompanying editorial, Dr. Michael D. Iseman and Dr. Leonid B. Heifets of the National Jewish Medical and Research Center in Denver noted that in some remote regions, doctors discover a patient's drug resistance only when the person's symptoms fail to subside. This, they said, can mean a loss of nine to 12 months of valuable time when the patient could be treated appropriately.

The new TB test, called microscopic-observation drug-susceptibility (MODS), was developed by Peruvian doctors and then tested on patients at a Hopkins-run laboratory in Lima. In today's study, doctors reported that the test generally produced results in 10 to 14 days, with some results coming earlier than that.

It then takes several days more to complete resistance testing - but in the end, patients can get started on the right medications more than a month earlier than was previously possible.

"With the increasing amount of drug resistance, we desperately need to improve the tools used in diagnosis," said Dr. Lee B. Reichman, executive director of the New Jersey Medical School Global Tuberculosis Institute.

Though he hadn't yet read the study, Reichman said the rapid turnaround would be a "phenomenal" advance in stemming the spread of TB and its resistant strains.

Multi-drug resistance became a major problem in the 1990s, owing largely to the failure of some patients to receive and take their medications on schedule. This gives the rapidly changing bacteria a chance to morph into strains that defy conventional drugs. The term multi-drug resistance applies to strains that resist two or more medications.

Patients who have resistant strains can be switched to second-line drugs that are more expensive and toxic. Recently, world health authorities have raised concern about strains - called extensively resistant - that defy almost all second-line drugs.

In an alert this week, the World Health Organization said the stubborn strains are threatening Eastern European countries where AIDS emerged after the fall of the Soviet Union, the Associated Press reported. Fourteen of the 20 countries in the world with the highest rates of resistant TB are in Europe, according to a recent survey by the U.S. Centers for Disease Control and Prevention.

The extensively resistant strains have also emerged in Africa and Asia, the regions that have the world's highest incidence of TB.

The old and new tests each rely on a patient's sputum sample applied to a growth medium in a dish.

The older test uses a Lowenstein-Jensen culture, which is solid. After a month or more, lab technicians can see a bacterial growth if it was originally present in the patient's sputum.

"Most of the time, you just find the culture by your naked eye," Gilman said. "All of a sudden, you see this tan colony growing - that's TB." To test for resistance, lab technicians then apply antibiotics to separate cultures. If the bacteria still grow, the strain is resistant.

Instead of a solid growth medium, the new test utilizes a broth in which the bacteria grow faster. Scientists taking part in the study discovered that they can see the bacteria under a microscope within several days.

"It looks like little tangles when it first comes out," Gilman said. "Nothing else really looks like that."

If the test for resistance is positive, doctors still must switch the patient to other drugs but without nearly as long a delay.

Scientists chose not to patent the test so labs throughout the world could freely adapt and use it, Gilman said. Laboratories must set up work stations equipped with hoods, exhaust fans and filters that protect lab workers from inhaling the bug.

Gilman said many TB labs may already have this equipment, which can cost upward of $7,000, but not a specialized microscope that can cost $4,000.

Some countries might not be able to afford microbiology labs even if they are inexpensive by Western standards, said the authors of the editorial. They suggested that health groups make provision of such laboratories "one of the urgent priorities in the global fight against tuberculosis, especially in countries with limited resources."

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