Disinfection is the operation following washing and prior to sterilisation. It is becoming increasingly important in the fight against nosocomial infections in healthcare facilities.

Thermal disinfection is the recommended method for all critical medical devices; accordingly, the future European and international standards are logically defining this concept that had remained vague for such a long time.

Appendix A of the future PrEN 15883-1 standard recognises that a lethal effect against microbial flora is ascertained beyond 65°C.

Following the example of the Fo sterilisation value concept, a new concept for evaluating the efficacy of thermal disinfection known as Ao was created in order to standardise the various practices and definitions existing in different countries up to now.

The value is determined in a matter of seconds, and represents the integral of the cycle temperature/time curve starting at 65°C and up to the end of the disinfection plateau.

The recommended Ao values for prEN 15883-1 and Ð2 are 600 s for medical devices in contact with intact skin and 3000 s for critical medical devices.

To obtain the required values, several temperature-time pairs are possible, for instance:

• For a 600-second Ao:

- 10 min at 80°C
- 3 min 10 s at 85°C
- 1 min at 90°C
- 30 s at 93°C

• For a 3000-second Ao:

- 50 min at 80°C
- 16 min at 85°C
- 5 min at 90°C
- 2 min 30 s at 93°C

HOSPITALIA washer disinfectors are equipped with 4 certified preset programs with the following Ao values:

instruments and anaesthetics: . . . 3000-second Ao, disinfection plateau at 90°C for 5 min. trays/containers and clogs: . . ..600-second Ao, disinfection plateau at 85°C for 3 min. 10 s.

The Lancer programs are designed to obtain an Ao value as of the moment when the indicated disinfection temperature is reached (85°C or 90°C).
Thus, they provide a buffer margin of safety. Any deviation from the disinfection temperature during the plateau is automatically detected and signalled by an alarm.