Fecal concentration of Rhodococcus equi determined by quantitative polymerase chain reaction of rectal swab samples to differentiate foals with pneumonia from healthy foals.

Background: Diagnostic accuracy of real-time, quantitative PCR (qPCR) assays to quantify virulent Rhodococcus equi using rectal swab samples has not been systematically evaluated.

Objective: 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.

Animals: One hundred privately owned foals born in 2021 from 2 farms in New York.

Association of pneumonia with concentrations of virulent Rhodococcus equi in fecal swabs of foals before and after intrabronchial infection with virulent R. equi.

Background: Intragastric administration of virulent Rhodococcus equi protects foals against subsequent experimental intrabronchial (IB) infection, but it is unknown whether R. equi naturally ingested by foals contributes to their susceptibility to pneumonia.

Hypothesis: Fecal concentration of virulent R.