15 Million Americans Said
Infected With TB - Most
Are 'Inactive'
CHICAGO (AP) -- Even the most successful programs to combat tuberculosis fail to eradicate as many as a third of new infections, pointing to the need for new strategies, researchers said in a new report.
A program implemented in Baltimore used state-of-the-art techniques to cut the city's TB rate from one of the highest in the nation to one of the lowest. It was among the first to implement directly observed therapy and aggressive contact tracing.
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.
"It suggests that to bring TB rates down from low to even lower, or if one wants to think of eradication, more is going to be needed," Dr. William R. Bishai, the study's lead author, said in a telephone interview Monday.
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.
But in the 2 1/2 years ending in 1996, new infections still accounted for about one-third of all diagnoses, with the remainder being old infections that had just begun to cause illness, researchers said.
The new cases clustered mostly in areas with high rates of poverty, poor education, drug abuse, alcoholism and the AIDS virus, where TB control has traditionally been difficult, the researchers said.
"A lot of the recently transmitted TB appeared to be transmitted casually -- probably between people who didn't know one another's identities," said Bishai, assistant professor of international health at Johns Hopkins University School of Hygiene and Public Health.
Contract tracing wouldn't help those people, Bishai said.
An expert not involved in the study noted that other cities have tried the same TB-control measures for shorter periods and have found the same thing.
Creative approaches will be needed, said the expert, Dr. Peter F. Barnes of the University of Texas Health Center at Tyler.
One technique could use DNA fingerprinting to locate clusters of new infections, and then an old approach -- chest X-rays -- to screen everyone in the cluster for unidentified active cases, he said.
By BRENDA C. COLEMAN, AP Medical Writer