Companies that make reusable, snakelike cameras to examine patients internally should begin making disposable versions, because the current models cannot be properly sterilized and have spread infections from one patient to another, the Food and Drug Administration said on Thursday.

In the meantime, hospitals that use the instruments, called duodenoscopes, should start to transition to models with disposable components to reduce the risk of infection to patients, the agency said.

Duodenoscopes, which are used in about 500,000 procedures a year in the United States, have been implicated in hospital outbreaks sickening hundreds of patients. Tests ordered by the F.D.A. found that one in 20 harbored disease-causing microbes like E. coli even after being properly cleaned.

Duodenoscopes are long fiber-optic devices that are inserted into the upper part of the small intestine through the mouth; the instruments are used in patient after patient. Though they are cleaned, they cannot be sterilized with steam heat and are instead hand-scrubbed and then put in dishwasher-like machines that use chemicals for disinfection.