Implementation of a molecular typing system to support epidemiological investigations in the tuberculosis health care system in Vienna

Tuberculosis continues to be one of the predominant infectious diseases. Ef fective control of its spread requires that sources of infection and routes of transmission be disclosed as quickly as possible. At present such inves tigations are still performed by conventional epidemiological methods. In t he recent past, however, molecular typing systems were added to the spectru m of epidemiological tools. Unfortunately, they were applied to retrospecti ve investigations rather than used as an aid in the health care system. In this study, 515 Mycobacterium tuberculosis strains isolated during 1997 and 1998 in Vienna were analysed by spoligotyping, a molecular technique re quiring no further cultivation of mycobacteria. The study was aimed to asse ss the suitability of the method as a quick means of disclosing new cases. Thus, clusters obtained by spoligotyping were analysed along with demograph ic and epidemiological data and compared with clusters obtained by conventi onal epidemiological techniques alone. In addition, spoligotype-forming clu sters were matched with an international database containing spoligotypes f rom four different studies. Of 515 isolates, 107 showed an unique pattern. The remaining 408 isolates w ere distributed into two large clusters of 82 and 73 isolates and into 49 s maller ones consisting of 2 to 33 isolates each. The two spoligotypes formi ng the large clusters were identical with the most prevalent spoligotypes i n the world. Therefore, for the tuberculosis authorities, information was o nly gained by exeluding rather than tracing possible ways of transmission. Twenty-two of the 49 spoligotypes forming smaller clusters were identical w ith strains found in other parts of the world. Seventeen of 22 infection ch ains assumed by conventional investigations were confirmed by spoligotyping . in small clusters, an additional 24 infections were assumed due to simila rities such as living conditions or socioeconomic status. In 27 clusters, a il patients sharing the same strain belong to the same country or geographi cal area. In conclusion, spoligotyping proved suitable as an early guide in conventio nal investigations to trace routes of M. tuberculosis transmission in a com munity. However, when a strain isolated from a patient belongs to a spoligo type shared by many isolates, a second molecular typing method is required.