October 29, 1996|By Dr. Simeon Margolis | Dr. Simeon Margolis,SPECIAL TO THE SUN
One of my close friends is extremely sick with tuberculosis, I thought that tuberculosis was easily cured with antibiotics and was no longer a major health problem.
No single infectious disease causes more deaths than tuberculosis (TB).
Throughout the world about 1 billion people are infected with tuberculosis; there are 8 million new cases and 3 million deaths annually. The incidence of TB in the United States had been declining for decades until the mid-1930s when an upsurge in cases began. Presently, about 25,000 new cases are reported in this country each year.
TB spreads when coughing by infected individuals releases TB bacteria into the air. New infections then arise in the lungs of others when they breathe in these bacteria. Transmission requires close contact with infected people, often in a poorly ventilated, closed environment.
As a result, new cases are more likely in prisons and with overcrowded living conditions. Most often the initial lung infections with TB causes no illness because the body's immune system kills most of the bacteria and stops progression of the disease. Not all of the bacteria are killed, however, and the dormant ones can become reactivated and cause disease if the immune system weakens.
Because their immune systems function very poorly, AIDS patients are highly susceptible to TB and develop clinical illness shortly after the initial infection.
You are right that a number of drugs are effective in treating TB. The most commonly used drugs are isoniazid (INH), rifampin, pyrazinamide and streptomycin. Unfortunately, there has been a frightening rise in tuberculosis bacteria that are resistant to the actions of one or several of these anti-TB drugs (multidrug resistance).
The importance of proper treatment and the impact of drug resistance are evident from the following fatality rates for tuberculosis: untreated, 50 percent; treated, 4 percent; treated when multidrug-resistant organisms are present, and the immune system is intact, 40 percent; or weakened such as in AIDS patients, 80 percent.
Resistance to a drug results from a random mutation in the genes of a small number of the infecting TB bacteria. Since bacteria are likely to have the two different mutations that are needed to confer resistance to two drugs, the treatment strategy for TB is to use at least two, and often, three different drugs as soon as the disease is diagnosed.
Treatment of tuberculosis with resistant strains of the bacteria must be continued for at least six months.
Resistant strains arise when patients do not take all of their drugs or discontinue treatment prematurely or when doctors fail to prescribe multiple drugs. One approach shown to improve compliance with drug treatment is implementations of programs, termed Directly Observed Therapy, in which the staff watch patients as they take their daily medications.
A large increase was observed in the number of multidrug-resistant strains when these programs were temporarily abandoned for lack of federal funds in the early 1980s.
About 10 percent of TB strains now show drug resistance in the United States and as many as 20 percent of strains recently isolated in New York exhibited multi- drug resistance.
A major problem in the treatment of TB is the time required to make a definitive diagnosis, even when the disease is strongly suspected. And it takes many weeks before laboratory studies are able to determine whether the infecting bacteria are multidrug resistant.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.
Pub Date: 10/29/96
