Guide to the Application of Genotyping to Tuberculosis Prevention and Control

Developing a Tuberculosis Genotyping Program

Special Issues

Continuity Between Past Genotyping Activity and New Genotyping Programs

Many programs have IS6110-based RFLP results on a large number of isolates. It will not be possible for the new genotyping laboratories to perform spoligotyping and MIRU analysis on a large number of previously collected isolates. But if the TB program has on-going outbreaks that have been documented by genotyping and you believe there may be additional cases in the future, a single isolate from each outbreak may be submitted for genotyping. A reasonable definition of an outbreak is a cluster of at least four patients who have matching genotypes that includes at least one patient who received a TB diagnosis within the last 3 years. A notation that these isolates came from previous outbreak cases should be made in the “Comments” field of the TB Genotyping Isolate Submission Form.

Evaluation of the Usefulness of Genotyping

The TB program should collect data that allow an evaluation of the impact of the genotyping program on their TB control practice. Consider the following as helpful items to track:

• Unsuspected outbreaks identified through genotyping.
• False-positive cultures identified through genotyping.
• Epidemiologic links between two TB cases that were identified during contact investigations and later confirmed or refuted by subsequent cluster investigations.
• New epidemiologic links that were identified during cluster investigations but not discovered during previous contact investigations.

These data can be used to evaluate the impact of the genotyping activity. It should be noted that the value of genotyping for detecting unsuspected transmission increases over time. The minimum time needed for establishing a background of genotypes for an area is 2–3 years.