Molecular epidemiology of tuberculosis among immigrants in Hamburg, Germany

To study the characteristics of tuberculosis (TB) in foreign-born individuals living in Hamburg, Germany, and to discover in what way foreign-born individuals contribute to the incidence of TB in Hamburg, an in-depth epidemiological study was performed by a combination of classical and molecular methods. In total, 796 patients with TB were analyzed between 1997 and 2002 (88.7% of all patients with culture-positive TB in the study period). Of this total, 334 were foreign-born patients from 43 different countries. Of these, only 31 cases were identified as a consequence of the screening of 12,176 asylum seekers at entry. Of the foreign-born patients, 41.9% had been living in Germany for more than 5 years. On the basis of the IS6110 typing results for isolates from all patients, 246 patients (31%) were classified into 68 clusters, with each cluster containing from 2 to 38 patients. Among foreign-born individuals, 86 (26%) were represented in 40 clusters. In multi-variate analyses, a previous history as a TB contact had the highest predictive risk for clustering among foreign-born patients, followed by drug addiction, alcohol dependence, being an asylum seeker, and unemployment. Epidemiological links verifying recent transmission could be confirmed for 39 of the 86 foreign-born members (45.3%) who formed a cluster, comprising 16 source patients and 23 directly infected patients. Of 2,227 previously known contacts of foreign-born patients subjected to traditional contact investigation, 14 foreign-born individuals (0.6%) subsequently contracted culture-confirmed TB, but only 9 transmissions could be confirmed by IS6110 typing (39.1% of the 23 confirmed fresh infections retrospectively confirmed by IS6110 typing). In conclusion, only a minority of TB cases among foreign-born individuals are detected by screening of asylum seekers or conventional contact tracing. Recent transmission does not play an important role in TB among immigrants in Hamburg.