Diagnostic accuracy of real‐time, quantitative PCR (qPCR) assays to quantify virulent Rhodococcus equi using rectal swab samples has not been systematically evaluated.
To evaluate the accuracy of qPCR of rectal swab samples to differentiate foals with pneumonia from healthy foals of similar age from the same environment.
An incident case‐control study design was used. Rectal swabs were collected from all foals diagnosed with R. equi pneumonia at 2 horse‐breeding farms (n = 47). Eligible pneumonia cases (n = 39) were matched by age to up to 2 healthy (n = 53) control foals; rectal swabs were collected from control foals on the day of diagnosis of the index case. DNA was extracted from fecal swabs and the concentration of virulent R. equi (ie, copy numbers of the virulence‐associated protein A gene [ vapA] per 100 ng fecal DNA) was estimated by qPCR.