Infectivity of scrapie prions bound to a stainless steel surface

Background: The transmissible agent of Creutzfeldt-Jakob disease (CJD) is not readily destroyed by conventional sterilization and transmissions by surgical instruments hale been reported. Decontamination studies have been carried out thus far on solutions or suspensions of the agent and may not reflect the behavior of surface-bound infectivity. Materials and Methods: As a model for contaminated surgical instruments, thin stainless-steel wire segments were exposed to scrapie agent, washed exhaustively with or without treatment with 10% formaldehyde, and implanted into the brains of indicator mice. Infectivity was estimated from the time elapsing to terminal disease. Results: Stainless steel wire (0.15 X 5 mm) exposed to scrapie-infected mouse brain homogenate and washed extensively with PBS retained the equivalent of about 10(5) LD50 units per segment. Treatment with 10% formaldehyde for 1 hr reduced this value by only about 30-fold. Conclusions: The model system we have devised confirms the anecdotal reports that steel instruments can retain CJD infectivity even after formaldehyde treatment. It lends itself to a systematic study of the conditions required to effectively inactivate CJD, bovine spongiform encephalopathy, and scrapie agent adsorbed to stainless steel surfaces such as those of surgical instruments.