Efficacy of high‐level disinfection of endoscopes contaminated with Streptococcus equi subspecies equi with 2 different disinfectants

Abstract Background Prevention of spread of Streptococcus equi subspecies equi (S. equi) after an outbreak is best accomplished by endoscopic lavage of the guttural pouch, with samples tested by culture and real time, quantitative polymerase chain reaction (qPCR). Disinfection of endoscopes must eliminate bacteria and DNA to avoid false diagnosis of carrier horses of S. equi. Hypothesis/Objectives Compare failure rates of disinfection of endoscopes contaminated with S. equi using 2 disinfectants (accelerated hydrogen peroxide [AHP] or ortho‐phthalaldehyde [OPA]). The null hypothesis was that there would be no difference between the AHP and OPA products (based on culture and qPCR results) after disinfection. Methods Endoscopes contaminated with S. equi were disinfected using AHP, OPA or water (control). Samples were collected before and after disinfection and submitted for detection of S. equi by culture and qPCR. Using a multivariable logistic regression model‐adjusted probability, with endoscope and day as controlled variables, the probability of an endoscope being qPCR‐positive was determined. Results After disinfection, all endoscopes were culture‐negative (0%). However, the raw unadjusted qPCR data were positive for 33% AHP, 73% OPA, and 71% control samples. The model‐adjusted probability of being qPCR‐positive after AHP disinfection was lower (0.31; 95% confidence interval [CI], −0.03‐0.64) compared to OPA (0.81; 95% CI, 0.55‐1.06), and control (0.72; 95% CI, 0.41‐1.04). Conclusion and Clinical Importance Disinfection using the AHP product resulted in significantly lower probability of endoscopes being qPCR‐positive compared to the OPA product and control.