An animal model for checking instrument sterilisation

In vitro assessment of sterilisation and disinfection processes using bacteria as test organisms are the basis of recommendations for clinical practice. It has been difficult to test efficacy against viruses, or to determine the effect of blood and other body fluids.We used duck hepatitis B virus which is similar to the human agent to test the efficacy of autoclaving on dental syringes. Low levels of virus (sufficient to infect 1/16 ducklings) survived high temperature/short cycle autoclaving of syringes which had been contaminated to mimic 'in use' conditions.Electronmicroscopy showed extensive biofilm formation on the luminal surface of used dental syringes, and this protects organisms against destruction by chemical and physical agents. It is also difficult to remove by cleaning.We believe that routine cleaning procedures must be rigorous and that clinical guidelines for sterilisation and disinfection should incorporate a significant margin in excess of the conditions based on conventional in vitro tests.