TB Still a Deadly Health Threat
Rates are highest in developing nations, but U.S. not immune
TUESDAY, June 7, 2005 (HealthDay News) -- Tuberculosis remains a deadly health threat, affecting one of every three people worldwide, with 9 million new cases every year and 2 million deaths.
Yet most North Americans think the disease has been eradicated. To which Dr. Catherine DeAngelis, editor of the Journal of the American Medical Association, said at a press conference Tuesday, "If you still believe that, I have a bridge I want to sell you."
The June 8 issue of the journal is a special theme issue, devoted entirely to the global burden posed by tuberculosis. While rates of infection have been falling steadily in developed nations, more than half of all TB cases now occur in five countries: Bangladesh, China, India, Indonesia and Nigeria.
"It's what I consider to be the plague in the world today," said DeAngelis, adding that HIV/AIDS is helping to fuel the epidemic because infected people with the AIDS virus are more prone to becoming ill from tuberculosis.
Tuberculosis is caused by bacteria called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but can also attack any part of the body, such as the kidney, spine, and brain. If not treated properly with drug therapy, TB can be fatal, according to the U.S. Centers for Disease Control and Prevention.
While the bulk of TB cases are clustered in the developing world, the developed world isn't immune. California led the United States in the number of TB cases in 2003.
The good news for Americans is that the number of overall cases has declined over the past decade -- more than 14,000 cases were reported in 2003 in the United States. The bad news is that multi-drug resistant (MDR) cases are staying stubbornly stable, at about 1 to 2 percent of all cases.
Drug-resistant tuberculosis is generally harder and more expensive to treat than "regular" TB.
"It requires 18 to 24 months of prolonged, complicated and toxic therapy," said Dr. Reuben M. Granich of the U.S. Centers for Disease Control and Prevention, and lead author of the study on drug-resistant TB that appears in the journal.
"It's really difficult to treat and much more likely to be fatal. It's hazardous, has a more prolonged infectious period, it's harder to kill the bacterium and people spread it for longer periods of time," he added.
To get a handle on the characteristics of MDR tuberculosis with an eye toward controlling it, Granich and his colleagues looked at records of more than 38,000 cases of TB and 407 cases of MDR tuberculosis reported to California health authorities.
People with MDR tuberculosis were seven times more likely to have been treated previously for TB, making this the highest risk factor for developing resistant strains of the bug (as opposed to becoming directly infected with a resistant version of the disease). People with MDR tuberculosis were also less likely to have completed drug therapy than people with other forms of the disease, Granich said.
The majority (83 percent) of MDR tuberculosis cases occurred in people who had been born outside the state, in 30 different countries, the study found.
The authors suggested that physicians look for resistant TB in people who are Asian and/or Pacific Islanders, who were born outside the United States, and in those who report prior treatment for tuberculosis.
A second study found that, contrary to conventional wisdom, chest X-rays of people with tuberculosis do not reflect how recently the disease was acquired.
"Immune function [specifically, HIV status] has more to do with chest X-ray appearance," said Dr. Neil Schluger, of Columbia University Medical Center in New York City, who was co-author of the study. "Atypical patterns of TB on an X-ray represent atypical immunity and should not make an estimate of when someone became infected."
Three things can happen when a person is exposed to TB germs: the person can eliminate or kill the germs; he or she can inhale them and contain them for a "latency" period which might become active many years later; or the individual could get sick much more quickly, the study found.
For years, experts had believed that "typical" X-ray patterns -- in which the disease appears primarily in the upper part of the lung and is accompanied by cavities where lung tissue had been destroyed -- was indicative of TB contracted a while back that remained latent. Atypical X-rays, which show swollen lymph nodes but nothing in the upper part of the lungs, were supposed to indicate disease encountered relatively recently.
After using molecular fingerprinting of the bacteria, patient interviews and chest X-rays of 546 patients at a New York City hospital, researchers discovered that these past assumptions were wrong.
"We found the opposite of what's generally held to be the teaching: that recently transmitted cases are not associated with atypical X-ray patterns of disease, and the only factor which predicted a difference was HIV status, which we took to be a surrogate for immune function generally," Schluger said. "You can't tell by looking at an X-ray pattern when that person came into contact with a case of infectious TB."
The finding has implications for TB-control strategies, Schluger added.
Several other studies in the same issue of the journal looked at different facets of TB. One study found that the drug isoniazid reduced the incidence of tuberculosis among male, HIV-infected miners in South Africa by 32 percent.
A World Health Organization representative said that goals for reducing the number of TB cases and deaths worldwide are still achievable by 2015, but that Africa and Eastern Europe represent the biggest challenges. The goals include detecting 70 percent of cases and treating 85 percent successfully.
To learn more, visit the U.S. Centers for Disease Control and Prevention.