Recent transmission of tuberculosis in Madrid: usefulness of molecular techniques

BACKGROUND: Recent studies suggest that many tuberculosis cases in urban ar eas result from recent transmission. The aim of this study was to determine patterns of tuberculosis transmission in Madrid. PATIENTS AND METHODS: A prospective population-based molecular epidemiologi cal study of patients diagnosed of tuberculosis was conducted in three urba n districts of Madrid (455.050 inhabitants) during 1997-1998. Clinical, dem ographic and epidemiological data were reviewed. Patients were included in clusters when their isolates contained: al six or more IS6110 bands in an i dentical pattern, or bl five or fewer IS6110 bands that matched identically and had an identical spoligotyping pattern. RESULTS: Of 207 positive-culture patients, 148 (71,5%) were DNA fingerprint ed. A total of 18 clusters which included 62 patients (41,9%) were identifi ed. Clusters Contained between 2 and 12 cases. Risk factors for clustering included: age < 35 years (OR = 4,1, 95% CI: 1,9-8,9), injection drug use (O R = 4,7, 95% CI: 1,6-14,8), HIV infection (OR = 2,7, 95% CI: 1,1-6,8), and a history of imprisonment (OR = 2,9, 95% CI: 1,2-7,2). The epidemiological investigation identified connections among 27% of clustered patients. CONCLUSIONS:: A high proportion of cases of tuberculosis in urban Madrid re sult from recent transmission. Molecular epidemiology studies give valuable information for urban tuberculosis control.