GENEVA- The discovery in 1944 of streptomycin, a drug which effectively cured tuberculosis, was greeted with tremendous enthusiasm and hope that the disease could be eradicated. Now 50 years later, public health authorities are pessimistic about the growing increase in tuberculosis cases throughout the world.

Ninety million new cases of TB will be diagnosed and 30 million people will die of the disease in this decade, according to the latest projections from the World Health Organization. The two main factors contributing to the increasing rise in tuberculosis cases are AIDS and the rise of drug-resistant forms of the disease. Homelessness and declining public health services are also believed to be factors in the U.S.

The number of cases of tuberculosis declined steadily in the US after WWII until the trend reversed course in the mid-1980's. The number of cases of TB has increased in U.S. from two per 100,000 to more than 10 per 100,000 now. The increase in TB correlates closely with the spread of the AIDS epidemic. In Europe, the highest TB rates are found in Portugal, while Denmark has the lowest.

Tuberculosis has also reached epidemic proportions in many parts of the developing world. Central Africa, Southeast Asia and parts of the Western Pacific have been severely affected. HIV infection is considered the primary cause of the TB explosion in these areas.

The problem in the US is not just more cases of TB, but more cases of the most difficult to treat form of the disease, multi-drug resistant (MDR) TB. This form of the disease is caused by variants of M. tuberculosis (the organism that causes TB) which are resistant to standard treatments including isoniazid, rifampin and ethambutol.

Patients most likely to develop MDR-TB are those who have been treated for TB in past but who failed to complete conventional treatment regimens. Nearly half of TB patients seen in some New York hospitals present with MDR-TB. Patients with AIDS and MDR-TB have poor prognoses, with mortality rates as high as 89% within 16 weeks of diagnosis.

MDR-TB is also a threat to US healthcare workers, having killed several in recent years. Factors associated with hospital related infection include delayed diagnosis and treatment, poor infection control and inadequate ventilation.

The treatment and prevention of MDR-TB is based on susceptibility testing of isolates, and may require the use of seven or more drugs. However, appropriate therapy for MDR-TB is often delayed because of the length of time required for conducting drug susceptibility tests, up to six months.

Conventional TB and MDR-TB both require aggressive drug therapy. It can cost up to $250,000 to cure a single case of MDR-TB, almost 100 times as much as treating conventional TB. In both forms of the disease, treatment may be required for six months or longer. Premature cessation of treatment not only leads to treatment failure, but to development of more resistant strains.

The necessity of long term treatment has led to the controversial use of almost forgotten laws allowing public health authorities to detain patients against their will, making sure they take every pill prescribed over a six to twelve month period. Such treatment, called 'directly observed therapy', has been used to treat patients not considered capable of following the recommended regimens.

The CDC has initiated an action plan which involves strategies to improve detection and treatment of active cases of TB across the country. The CDC plan also calls for earlier identification of patients with latent TB who are at risk for developing TB, such as AIDS patients. The American Medical Association has proposed routine HIV testing for all TB patients, as well as routine TB tests for all HIV patients. The AMA also advocates more aggressive contact tracing.

Public health authorities have expressed frustration over the medical world's inability to eradicate TB. The rise of MDR-TB is largely attributed to sloppy treatment practices throughout the world with drug regimens which otherwise would have been effective. Moreover, a vaccine has been available for many years, but is underutilized.

"We are not using existing tuberculosis drugs effectively, and we are not developing the new drugs we need. Anti-TB drugs discovered decades ago are sitting on the shelf, even though they are nearly 100 percent effective and cost as little as $13 for six months worth of treatment,'' said Dr. Arata Kochi, manager, WHO TB program.

TB is caused by exposure to Mycobacterium tuberculosis, a species of rod-shaped bacteria. Transmission occurs via exposure to airborne particles produced in the sneezes and coughs of infected patients. The most common site of infection is the lungs. Nearly 90 percent of TB cases are the result of a dormant infection becoming active when the host immune system weakens. TB has become one of the leading causes of death among people with AIDS.

On the research front, French and British researchers have identified a gene associated with drug resistance. This discovery could offer potential new strategies for drug development, and may also speed development of a much need rapid test for determining drug resistant strains of TB.

SOURCES: Journal of the American Medical Association, 1/18/95, v.273, No.3, 220-226. Heart Lung, 1993;22:365-369. FDA Online documents.

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