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Guide to the Application of Genotyping to Tuberculosis Prevention and Control
Developing a Tuberculosis Genotyping Program
Comparing Genotyping Results Between Jurisdictions
Experience has shown that most TB transmission occurs within a single TB program’s jurisdiction. On the basis of this experience, the genotyping laboratories will consider the genotyping results from each TB program separately when they look for genotyping matches. In other words, the genotyping laboratories will identify genotyping matches only among isolates that came from patients residing within the jurisdiction of a specific TB program.
Although this policy will identify almost all important genotyping matches, there will be instances of interjurisdictional TB transmission that are not detected. The NTCA/CDC Advisory Group on Tuberculosis Genotyping is working to develop possible ways to identify and alert TB controllers about possible interjurisdictional TB transmission. Whatever system is adopted, it will be important to consider epidemiologic data in addition to genotyping data in order to make decisions about the need for further investigations.
The following interim plans will help TB programs identify interjurisdictional TB transmission while we work on a comprehensive approach. CDC will review all genotyping laboratory reports as they are submitted to detect any instances of interjurisdictional genotyping matches. Depending on how unusual the genotyping pattern is (common genotyping patterns are less likely to represent recent transmission than never-before-seen patterns), on the geographic distribution of the genotyping cluster (interjurisdictional matches among adjacent TB programs are more likely to represent recent transmission than matches from TB programs that are widely separated), and on information about epidemiologic links that have been discovered by TB programs, CDC will notify TB programs of the interjurisdictional genotyping matches that are most likely to represent recent transmission. As experience with the new PCR genotyping methods grows and we learn more about the utility of identifying interjurisdictional genotyping matches, we will modify this approach.
As another interim measure, TB programs can contact adjacent TB programs and exchange genotyping results. For example, if one TB program is interested in a particular genotyping cluster in their jurisdiction, they can ask the adjacent program whether they have detected isolates with the same spoligotype and MIRU type. Adjacent TB programs can also agree to form a network to share all their genotyping results. For example, genotyping results could be posted on a web site, or results could be shared routinely by e-mail. Anyone who belongs to the network could sort the results and easily identify cross-jurisdictional genotyping matches.
Initially, CDC announced that interested TB programs could request that the genotyping laboratory search its database for any matches that came from adjacent TB programs where interjurisdictional transmission had been documented. As a result of that announcement, CDC received an unexpectedly large number of requests, including from states that were not adjacent to each other. Because the benefit of matching results from large geographic areas is not yet known, CDC will not be able to accommodate all the requests it has received. As more is learned about the utility of searching for possible interjurisdictional genotyping matches, this policy will be reanalyzed.