Risk of tuberculosis transmission among healthcare workers

Data from a prospective molecular-epidemiological study (1997-2015) of patients with culture-confirmed tuberculosis in Hamburg, Germany, were evaluated to assess the occupational risk of Mycobacterium tuberculosis complex transmission in a low-incidence setting. Isolates of M. tuberculosis complex were genotyped using IS6110 restriction fragment length polymorphism analysis. Results of structured questionnaires, geographical mapping and additional patient interviews were used for confirming epidemiological links. Out of the 2393 cases, 918 (38.4%) were classified into 224 clusters comprising 2-70 patients per cluster. Among the 918 cluster members, epidemiological links could be confirmed in 340 (37.0%) patients. In total, 55 (2.3%) patients were healthcare workers; 26 healthcare workers remained unclustered, but 29 healthcare workers belonged to cluster groups. Conventional contact tracing performed before genotyping to identify sources of the reported index cases detected only 73 (3.1%) patients. Logistic regression analysis confirmed work in the healthcare sector as strongest predictor for clustering of patients with verified epidemiological links (odds ratio (OR) 3.1, 95% CI 1.6-5.9), followed by alcoholism (OR 2.3, 95% CI 1.7-3.2) and sputum smear positivity (OR 1.8, 95% CI 1.4-2.3). Immigrants were more likely to be cluster nonmembers (OR 0.3, 95% CI 0.3-0.5). Recent transmission in Hamburg within the 19-year study period was found to be strongly associated with working in a healthcare facility. Although clusters also include many "imported" strains from abroad or regional highly prevalent M. tuberculosis strains with no evident epidemiological connection, routine molecular-epidemiological survey is indispensable to optimising and controlling the effectiveness of TB control strategies in German healthcare settings.