Background: Recent studies suggest that many tuberculosis cases in urban areas 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 epidemiological study of patients diagnosed of tuberculosis was conducted in three urban districts of Madrid (455.050 inhabitants) during 1997-1998. Clinical, demographic and epidemiological data were reviewed. Patients were included in clusters when their isolates contained: a) six or more IS6110 bands in an identical pattern, or b) 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 fingerprinted. A total of 18 clusters which included 62 patients (41,9%) were identified. 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 (OR = 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 result from recent transmission. Molecular epidemiology studies give valuable information for urban tuberculosis control.