The rates of tuberculosis cases overall and of cases due to recently acquired tuberculosis infection in San Francisco have declined significantly in recent years, due to the effects of more intensive control measures.
A new study identifying the trend, led by researchers from the University of California, San Francisco, is reported in the new issue (June 15) of Annals of Internal Medicine.
The study is the first analysis using methodology called molecular epidemiology--which combines DNA fingerprinting techniques and conventional epidemiology--to track the disease within a defined population and then to determine the effect of interventions designed to halt tuberculosis. Covering 1991-97, the study examined the rate of TB cases overall within the City and County of San Francisco as well as rates within high-risk groups, such as persons infected with HIV.
"We found that the intensified TB control measures established in the early 1990s in San Francisco were associated with a decrease in TB case rates and in the rate due to recently acquired infection," said lead investigator Robert M. Jasmer, MD, UCSF assistant professor of medicine who treats patients in the Division of Tuberculosis Control at San Francisco General Hospital Medical Center.
Study findings showed annual TB rates decreased from a high of 51 per 100,000 persons in 1992 to 30 per 100,000 in 1997. The rate of cases due to recently acquired TB infection--known as clustered cases because these persons have identical strains of the TB bacteria--decreased per 100,000 from 10 in 1991 to 4 in 1997.
Caused by the organism Mycobacterium tuberculosis, TB is a chronic bacterial infection that usually causes disease in the lungs but also attacks other organs. It is spread through the air when a person with active TB disease of the lungs or larynx coughs and infected droplets are inhaled by others into the lungs.