The US Food and Drug Administration identified which of the following as a recurrent theme contributing to persistent contamination of flexible endoscopes and the transmission of infection?

A. Exposure of endoscopes to patients with antibiotic resistant bacteria
B. Increasing prevalence of immunocompromised patients
C. Failure to meticulously follow manufacturer's written instructions for processing
D. Damage to endoscopes caused by inexperienced personnel
E. Excessively long endoscopic procedure times