Genotyping in contact investigations: a CDC perspective

Genotyping of Mycobacterium tuberculosis isolates has been widely used to support investigations of outbreaks and as a tool for studying transmission dynamics and other aspects of tuberculosis epidemiology. Its applications to contact investigations are more limited. Targeted typing can be used to confirm or disprove suspected relationships among cases. Universal typing of isolates can be used to identify unsuspected transmission and broaden the scope of contact investigations. In order to properly use the results, one must understand the nature of the changes in the M. tuberculosis genome that produce the heterogeneity reflected in the genotypes, and understand the discriminatory power of the various methods. IS6110 fingerprinting provides the highest discriminatory power, but can be a slow process. Spoligotyping and MIRU-VNTR are PCR-based methods that provide faster turnaround and produce digital results that facilitate comparisons. Appropriately used, isolate genotyping can be a useful adjunct to standard contact investigations.