Tuberculosis (TB) already kills about the same number of people as HIV/AIDS worldwide. The bacterium that causes tuberculosis can be spread through the air, and we're losing our ability to treat the infection with antibiotics.
Dr. Robert Loddenkemper and Dr. Barbara Hauer of Germany reported that drug-resistant tuberculosis represents a new challenge. Today's cases are already more difficult to treat than the dreaded TB infections of the 1940s. Streptomycin, the first anti-tuberculosis drug, was introduced in 1944, and produced impressive results until the bacteria developed resistance to it. Other drugs introduced in the following two decades are para-aminosalicylic acid (1944), isoniazid (1952), pyrazinamide and cycloserine (1952), capreomycin (1960), ethambutol (1961), and rifampicin (1966). Today, isoniazid and rifampicin are the most powerful anti-tuberculosis drugs, and are considered first-line therapies. Approximately 5 percent of new cases are resistant to (at least) these two drugs, and are called multidrug-resistant tuberculosis (MDR-TB). Extensively drug-resistant tuberculosis (XDR-TB) is defined as infection resistant to these two plus at least one of the fluoroquinolone antibiotics and one of the injectable second-line drugs. A few cases have been reported of tuberculosis resistant to practically all antibiotics. These infections are designated extremely drug-resistant tuberculosis (XXDR-TB).
The cure rate is only 52 percent for MDR-TB, according to data from the Robert Koch Institute. XDR-TB is even more difficult to treat and cure. “Tuberculosis must be treated with a combination of antibiotics,” Loddenkemper and Hauer said. The bacteria can develop resistance to a single antibiotic fairly easily, but they are more susceptible to a combination of effective drugs. As resistance to more drugs develops, there are fewer options for combination treatment. In addition, many anti-tuberculosis drugs are poorly tolerated because of their side effects. The treatment period is long: six months for non-resistant TB, and up to two years for MDR-TB. Extensive patient education and counseling are necessary to obtain good treatment adherence.
Risk factors for drug-resistant tuberculosis include:
1. Prior treatment with anti-tuberculosis drugs,
2. Contact with MDR-TB patients, or immigration from an area where MDR-TB is common,
3. Imprisonment,
4. Possibly, HIV infection.
Dr. Yan Shao and colleagues at the Nanjing Medical University in China performed a study of drug-resistant tuberculosis in the Jiangsu province of China. They found 41 percent of the strains resistant to at least one antibiotic. MDR-TB was found in 17 percent of their sample. They recommended more resources to prevent and treat this emerging epidemic.
References:
1. Loddenkemper R et al, “Drug-resistant tuberculosis: A worldwide epidemic poses a new challenge”, Dtsch Arztebl Int 2010; 107(1-2): 10-19. http://www.ncbi.nlm.nih.gov/pubmed/20090877
2. Shao Y et al, “Epidemiology of anti-tuberculosis drug resistance in a Chinese population: current situation and challenges ahead”, BMC Public Health 2011; 11:110. http://www.ncbi.nlm.nih.gov/pubmed/21324205
Reviewed July 28, 2011
by Michele Blacksberg R.N.
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.