Identification of Francisella tularensis subsp. tularensis A1 and A2 infections by real-time polymerase chain reaction.

Francisella tularensis subsp. tularensis (type A) is subdivided into clades A1 and A2. Human tularemia infections caused by A1 and A2 differ with respect to clinical outcome; A1 infections are associated with a higher case fatality rate. In this study, we develop and evaluate TaqMan polymerase chain reaction (PCR) assays for identification of A1 and A2. Both assays were shown to be specific to either A1 or A2, with sensitivities of 10 genomic equivalents. Real-time PCR results for identification of A1 and A2 were in complete agreement with results obtained by pulsed field gel electrophoresis analysis or conventional PCR when specimens from sporadic tularemia cases and a tularemia outbreak involving both A1 and A2 were tested. In addition, outbreak samples not previously typed to the clade level could be classified as A1 or A2. The assays described here provide new diagnostic tools with a level of sensitivity not previously available for identification of A1 and A2 infections.