Guide to the Application of Genotyping to Tuberculosis Prevention and Control

Combining Genotyping and Epidemiologic Data to Improve Our Understanding of Tuberculosis Transmission

Comparing Genotyping Results from Three or More TB Patients

In the previous discussion, we focused on possible transmission between just two TB patients. When a genotyping cluster grows to include three or more patients, additional information becomes available that can shed light on how the patients’ cases might be related.

As additional TB patients are diagnosed and found to belong to a previously identified genotyping cluster, more information about possible epidemiologic links becomes available. The greater the number of leads an investigator has to follow-up, the greater the chance of identifying a shared link among patients in a cluster.

Data on additional patients is also helpful in identifying endemic strains that are often found in the absence of evidence of recent transmission. When a TB program first initiates a genotyping program, it will be difficult to identify endemic strains until data from many patients are gathered and analyzed. After several years, a TB program will be able to identify M. tuberculosis strains that are commonly detected in their area but are rarely associated with patients who share known epidemiologic links.