Setting: Mycobacterium tuberculosis strain CDC1551 outbreak area in Tennessee and Kentucky and selected locations in the USA.
Objective: Develop a PCR assay to distinguish the highly transmissible CDC1551 from strains which have similar 4-band IS6110 fingerprints.
Design: Compare the IS6110 insertion sites in CDC1551 with those in 10 isolates which have similar 4-band IS6110 fingerprints. Utilize unique characteristics of insertion sites in CDC1551 to design a multiplex PCR to identify this strain.
Results: A multiplex PCR was developed which targets an IS6110 insertion conserved in most IS6110 low copy number strains and a deletion within the direct repeat region adjacent to an IS6110 insertion. Of 139 isolates with similar 4-band fingerprints, the CDC1551 PCR pattern was generated by only the 14 outbreak associated isolates. Of 154 isolates with different fingerprints, only four generated the CDC1551 pattern and these could be distinguished from CDC1551 by their IS6110 fingerprint.
Conclusions: The multiplex PCR used in conjunction with the IS6110 fingerprint should be a useful tool to aid in the continued surveillance of the outbreak area and follow the spread of this highly transmissible strain of M. tuberculosis.