Figure 2.

Quantity of Mycobacterium tuberculosis (Mtb) DNA detected by polymerase chain reaction (PCR) correlates with known colony-forming units (CFUs) of Mtb. Stool from a healthy control without tuberculosis was spiked with 10-fold dilutions of H37Rv Mtb (N = 6 per concentration, N = 60 total). (A) Stool DNA was isolated and Mtb qPCR quantified (Pearson’s r = 0.998, P value < 0.0001). (B) The percent of assays that detected Mtb was plotted for each concentration. Using logistic regression, there was a 95% probability of detecting Mtb in samples containing at least 95.24 CFU/50 mg of stool (95% confidence interval [CI]: 84.87–105.6) (95% CI shown in pink). This figure appears in color at www.ajtmh.org.