But the two techniques did not stop the spread of the dangerous lung infection among casual contacts, researchers concluded in a report in Wednesday's Journal of the American Medical Association. In directly observed therapy, health workers observe patients take each dose of medicine during months of treatment to ensure none is missed. Patients may be required to take medicine daily or several times a week. Contact tracing requires health workers to question each patient to learn who he has exposed to the infection so that they can be notified and given preventive therapy. TB spreads mainly when infected people cough or sneeze bacteria into the air, where they are inhaled by others.
Incomplete therapy promotes drug-resistant bacteria, a growing problem.
Fewer than 20,000 new TB cases were diagnosed last year, but highly drug-resistant TB has turned up in 43 states. Tuberculosis can be deadly if untreated. An estimated 15 million Americans are infected with TB, but 85 to 90 percent are inactive and not infectious. No effective vaccine is available. Baltimore implemented directly observed therapy and contact tracing in 1981, and lowered its rate from more than 35 new cases per 100,000 people in 1981 to fewer than 15 cases per 100,000 people in 1996.