A community outbreak of tuberculosis in Southern Austria: lessons learned for a targeted use of molecular epidemiological methods and tuberculin skin testing

Use of PCR-based Mycobacterium tuberculosis genotyping to prioritize tuberculosis outbreak control activities

Genotypic analysis of Mycobacterium tuberculosis isolates is increasingly applied in direct support of tuberculosis outbreak control activities. This is facilitated by PCR-based strain typing methods that enable the genotypic characterization of samples containing small numbers of M. tuberculosis cells. By using DNA extracted directly from primary diagnostic cultures, PCR-based methods were applied to a tuberculosis outbreak investigation and to surveillance in King County, Washington. In the outbreak investigation, five epidemiologically linked M. tuberculosis isolates had a unique pattern at mycobacterial interspersed repeating unit (MIRU) loci 10 and 23 when the pattern was compared to the patterns in a local MIRU locus database. In order to quickly identify new cases involving this strain (termed SBRI10), targeted genotyping at these two loci was performed with cultures from epidemiologically associated tuberculosis cases. Isolates with the characteristic genotypes at loci 10 and 23 were further analyzed by use of a 12-locus MIRU panel and by repetitive-unit-sequence-based PCR (rep-PCR). Between May 2004 and January 2005, 82 cases were screened, of which 14 were identified for further analysis and 13 were confirmed to be infected with SBRI10. Between September 2005 and August 2006, surveillance universal genotyping was performed by using the 12-locus MIRU panel with DNA from primary diagnostic enrichment cultures. A total of 161 samples were submitted for analysis, and 156 were successfully typed. Fifty-one cases formed 18 presumptive clusters by MIRU locus typing. Of these, 30 cases were confirmed to be members of 11 clusters by rep-PCR. Presumptive genotypic data were available rapidly, sometimes within 2 weeks of diagnosis. In this fashion, PCR-based genotyping provided data that can be used to prioritize disease control activities.

Molecular epidemiology of tuberculosis: toy or tool? A review of the literature and examples from Central Europe

Genotyping has become an indispensable tool in medical microbiology and epidemiology. One of the first targets has been Mycobacterium tuberculosis. Over the past 15 years approximately 900 pertinent publications have substantiated the value of the genotyping approach for tuberculosis control. New insights into the understanding of the natural history of tuberculosis, especially regarding the frequencies of reactivation, reinfection or multiple infection entailed adaptations of pathophysiological concepts. However, assessment of recent transmission, outbreak analysis, and detection of laboratory contamination still form the genuine scope of genotyping. Detection of unsuspected clusters of cases can provide clues to search for further, undetected cases. Uncovering false positive cultures spares the risks and costs of unnecessary treatment and may reveal systematic laboratory weaknesses. Several European countries already profit from nationwide prospective fingerprinting. After providing genotyping results to public health officials, these were able to document epidemiological links for substantially more tuberculosis patients. On a global scale, strain families and particular strains have been identified, characterised and traced in their spread. The importation of Beijing-genotype multidrug-resistant M. tuberculosis into Central European countries will be described here as an example. The goal for further developments is the ability to compare isolates for epidemiological purposes in a single step that also comprises species determination, drug resistance testing and detection of pathogenicity factors.