A molecular epidemiologic analysis of tuberculosis trends in San Francisco, 1991-1997

Background: To decrease tuberculosis case rates and cases due to recent infection (clustered cases) in San Francisco, California, tuberculosis control measures were intensified beginning in 1991 by focusing on prevention of Mycobacterium tuberculosis transmission and on the use of preventive therapy. Objective: To describe trends in rates of tuberculosis cases and clustered cases in San Francisco from 1991 through 1997. Design: Population-based study. Setting: San Francisco, California. Patients: Persons with tuberculosis diagnosed between 1 January 1991 and 31 December 1997. Measurements: DNA fingerprinting was performed. During sequential 1-year intervals, changes in annual case rates per 100 000 persons for all cases, clustered cases (cases with M. tuberculosis isolates having identical fingerprint patterns), and cases in specific subgroups with high rates of clustering (persons born in the United States and HIV-infected persons) were examined. Results: Annual tuberculosis case rates peaked at 51.2 cases per 100 000 persons in 1992 and decreased significantly thereafter to 29.8 cases per 100 000 persons in 1997 (P < 0.001). The rate of clustered cases decreased significantly over time in the entire study sample (from 10.4 cases per 100 000 persons in 1991 to 3.8 cases per 100 000 persons in 1997 [P < 0.001]), in persons born in the United States (P < 0.001), and in HIV-infected persons (P = 0.003). Conclusions: The rates of tuberculosis cases and clustered tuberculosis cases decreased both overall and among persons in high-risk groups. This occurred in a period during which tuberculosis control measures were intensified.