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[14] Thermal Washer-Disinfectors - Investigating the Disinfection Effect with ThermologgersFor routine investigation of the effect of disinfection in washer-disinfectors with a disinfection step, thermoelectric procedures using temperature sensors are described in Standard prEN 15883-1 "Validation of washer-disinfectors", since these can be easily conducted, evaluated and documented on site. A PC and appropriate software as well as one or several thermologgers spanning at least the range 10 °C - 100 °C are required. The standard describes in detail the requirements to be met by the measuring instruments as well as execution of measurements for the various test steps. They supplement any existing in-process control of the washer-disinfectors because they measure independently and can be compared with the data of the in-process control, to the extent that the latter can be read. The A0 value concept "A" is defined as the equivalent time in seconds at 80 °C to produce a given disinfection effect. The D value is the time needed at a particular temperature to reduce the microbial count to 10% (by 1 log10 level). The z value is the increase in temperature needed to reduce the D value to 1/10. If the defined temperature is 80 °C and the z value is 10, the term A0 is used. The A0 VALUE of a moist heat disinfection process is the lethality expressed in terms of the equivalent time in seconds at a temperature of 80 °C delivered by that process to the product with reference to microorganisms possessing a z value of 10. This is the case for many microorganisms. For disinfection processes aimed at bacteria, including mycobacteria, fungi and heat-sensitive viruses, an A0 VALUE OF 600 is defined, corresponding to a hold time of 600 s = 10 min at 80 °C. The A0 value of 600 can also be achieved at 90 °C with a hold time of 1 min. Table 1 shows conversion of the A0 value of 600 to other temperatures according to Machmerth. If efficacy is to be ensured also against HEAT-RESISTANT VIRUSES, e.g. hepatitis B, an A0 value of 3000 must be chosen, corresponding to a temperature of 90 °C and a hold time of 5 min. It is recommended to select in general the A0 value of 3000 for programmes used to process surgical instruments. For the TYPE TEST for washer-disinfectors based on standard prEN ISO 15883-1 extensive temperature measurements are needed, which in some cases are repeated during the operational and performance qualification after installation of the appliance on site using loads defined by the operator. For the routine tests, the operator defines in a QUALITY ASSURANCE CONCEPT which machines are to be checked and how often and in what positions the measurements are to be conducted. Unlike in the case of microbiological methods with biological indictors as used for periodic testing, the results can be read at once. But they do not provide any information on the preceding IMPECCABLE CLEANING of products, which constitutes a precondition for reliable disinfection. Hence supplementary investigations for cleanliness must be carried out. While recording the temperature course for the entire process with thermologgers, important information is also gathered on the exposure time and on the temperature range traversed in the cleaning step.
Table 1 Conversion of the A0 values to other temperatures (after Machmerth)
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What measuring instruments and measurements are required for routine investigation of washer-disinfectors? STANDARD prEN DIN ISO 15 883-1 introduces A0 as a yardstick for the lethality effect against microorganisms in moist heat processes and defines the required temperatures and exposures times. THE TEMPERATURE MEASUREMENTS are performed between the items being cleaned so as to demonstrate that all inner and outer surfaces have been reached. A0 is the lethality time in seconds at 80 °C and a z value of 10. AN A0 VALUE OF 600 has been defined for processes aimed at bacteria, fungi and heat-sensitive viruses. It can be achieved with various combinations of temperatures and hold times. AGAINST HEAT-RESISTANT VIRUSES an A0 value of 3000 is required. This is generally recommended for processing surgical instruments. THE TYPE TEST calls for extensive temperature measurements. A QUALITY ASSURANCE CONCEPT defines which machines are to be tested and how often within the framework of routine testing. IMPECCABLE CLEANING is a precondition for reliable disinfection. |
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