The instruments, used to examine the lungs and digestive tract, were washed by hand and processed through a decontaminator reaching temperatures of more than 200 degrees, according to CPMC spokesman Dean Fryer.
However, for unknown reasons the instruments were not subjected to a final sterilization step, Fryer said.
"We have since corrected our sterilization processes, informed the patients involved and discussed this matter in detail with their doctors," Fryer said.
"The doctors were neither aware of nor responsible for this circumstance," he added.
An evaluation by an independent infectious disease expert concluded the risk of disease transmission was very low. However, the hospital has contacted affected patients and advised them to get tested for infectious diseases such as HIV and hepatitis as a precaution, Fryer said.
"We apologize to our patients and regret that this occurred," he said. "At CPMC, we remain dedicated to continuous improvement and committed to our patients."
A state Department of Public Health spokeswoman confirmed the agency had been notified of the issue, but said she could not comment on an ongoing investigation.