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Ongoing outbreak of tuberculosis in a low-incidence community: a molecular-epidemiological evaluation.

SETTING
Federal State of Hamburg, Germany, 1997-2002.


OBJECTIVE
To identify the pathways of tuberculosis (TB) transmission and to evaluate possible risk factors for recent transmission in Hamburg.


DESIGN
A prospective, molecular-epidemiological study was performed. Conventional contact tracing and an indepth epidemiological analysis were conducted.


RESULTS
A predominant cluster of Mycobacterium tuberculosis strains was identified by IS6110 DNA fingerprinting of 828 TB cases notified during the study period. The cluster expanded from seven cases in 1997 to 38 in June 2002. A single source case could not be identified. Transmission links were confirmed in 20 cases. Twenty-five patients were regular customers at a bar close to the red-light district. Seven patients, including one regular customer in the bar, were staying at a nearby hostel for homeless men, and four were living in a far-away hostel for alcoholic men. Of the 421 close contact persons investigated, 169 (40.1%) had positive tuberculin skin tests, and eight became ill (1.9%). Twelve of 20 cases with confirmed recent transmission could only be determined a posteriori by fingerprinting.


CONCLUSIONS
An ongoing outbreak at a local bar indicates chronic alcoholism as a high-risk factor for the dissemination of TB in a large metropolitan area. The fact that conventional contact tracing is insufficient for the detection of chains of transmission in this milieu indicates the need for an improved, location-based approach, e.g., the implementation of an outreach strategy.