Guide to the Application of Genotyping to Tuberculosis Prevention
Developing a Tuberculosis Genotyping Program
Comparing Genotyping Results Between Jurisdictions
Experience has shown that most TB transmission occurs within a
single TB programís 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.