Evaluation of Cleaning and Disinfection Processes Performed byAutomatic Washer/Disinfectors

Evaluation of Cleaning and Disinfection Processes Performed by Automatic Washer/Disinfectors

By Maria Do Carmo Noronha Cominato Bergo, RN, MS


Thermal washer-disinfectors represent a technology that brought about great advantages such as the establishment of protocols, standard operating procedures, and reduction in occupational risk of a biological and environmental nature. The efficacy of the cleaning and disinfection obtained by automatic washer/disinfector machines, in running programs with different times and temperatures determined by the different official agencies, was validated according to recommendations from International Organization for Standarization (ISO) Standard 15.883-1/1999 and HTM 2O3O (NHS States, 1997) for the determining of the minimum lethality and disinfection assurance level (DAL), both theoretically and through the use of thermocouples. In order to determine the cleaning efficacy, the Soil Test, Biotrace Protect and Protein Test Kit were used. The procedure to verify the colonyforming units (CFU) count of viable microorganisms was performed before and after the thermal disinfection. This article shows that the results are in compliance with ISO and HTM Standards. The validation steps confirmed the high efficacy level of the medical washer/ disinfector. This protocol enabled the evaluation of the procedure based on evidence supported by scientific research, and the possibility of developing further research.


Currently, there are several large-scale procedures to clean and disinfect devices used in a hospital environment, hence the need to study the efficacy of the washer/disinfector. Michels (1991) mentions the concern with the risk posed by the handling of devices without the use of adequate protective equipment and correct standard procedures, as well as the risk of environmental contamination from residues generated by the cleaning process. The cleaning of the work environment and devices must be perceived as of maximum importance, as incorrect execution triggers serious problems in downstream operations. Cleaning consists of the manual or mechanical removal of soil deposited on an inert surface.

Technology has evolved considerably in this field. There are various types of medical washers available ultrasonic, disinfectors, pasteurizers and sterilizer/washers. Furthermore, there have also been technological improvement in the process inputs such as enzymatic detergents, soil-residue tests, and tests to detect protein residue. In the European community, the thermo-disinfector washer machines operate at different temperatures and cycle times, which are determined by official regulatory agencies in the various European countries, making it difficult for our selection of the best program. (Fengler, 2001) There are no operating standards to guide the assessment of washer/disinfector machines in Brazil. For this reason, we have used the standards adopted in the equipments country of origin and the manufacturers specifications.

This investigation was developed to aid the nurses in the central supply (CS) department in choosing among the several different programs available for the automatic washer/disinfectors, and to provide scientifically supported procedures. The general objective of this study was to assess the efficacy of the cleaning and disinfection achieved by automatic washer/disinfector machines in operating programs with different cycle times and temperatures recommended by different regulatory agencies. The specific objectives were to assess the efficacy of the disinfection achieved by the automatic washer/disinfector in operating programs with different cycle times and temperatures; determine and analyze the lethality rate A0 and DAL in the equipment for the various disinfection programs suggested by different regulatory agencies in the different countries and comparing the results to theoretical results. (Jatzwauk, 1997)


This investigation was conducted in a laboratory using a quantitative approach. The ISO 15.883-1/1999 and HTM 2030 standards were used for guidance and methodology in conducting this investigation. The cleaning assessment was performed in the same manner for all programs investigated. The Soil Test and Biotrace Protect were evaluated in three cycles of mechanical cleaning. The Soil Test was applied to 313 devices. Of these, five presented Soil Test residues after a visual inspection. Due to their complex shapes, they were submitted to the Biotrace Protect protein residue test. The Biotrace Protect test was applied to 65 devices where 25 were evaluated at each cycle.

The Miele protein residue test was applied separately in three consecutive cycles of mechanical cleaning and 141 devices (47 in each cycle) were evaluated. The choice of the devices was made in accordance to guidelines from the HTM 2030 standard. In this investigation, the thermal qualification program was previously applied in order to assess the efficacy of the medical washer/disinfector and the operating programs. The application was done by the engineer responsible for the validation service, with supervision from the investigator.

The ISO 15883-1/1999 standard requires that for validation purposes, the cycles must be performed three consecutive times. Thus, each cycle had 20 contaminated devices submitted to three cycles for each protocol investigated. After the thermal disinfection was completed, the test devices were sent to the bromatology and chemistry area in the sterility section of the Adolfo Lutz Institute for identification of the viable microorganisms.

For this phase, an intentional contamination of 60 devices with blood from a placenta from a natural birth was done by keeping the device in contact with the placenta for one hour. This one-hour contact period was determined by considering the length of time actually dispended in intra-surgical time recorded, operating room disassembly, and the preparation of the material for cleaning and disinfection procedures.

After contamination, the excess residue was removed with a stream of pressurized cold water and placed between the two and three trays in the LTD support. The remaining trays were loaded with the contaminated material in the investigation itself. After the the usual disinfection cycle, gloves and two gamma-ray-sterilized polyethylene bags were used to remove the devices. Using aseptic technique, the devices were placed inside the bags, sealed, identified and subsequently conditioned in resistant polyethylene packaging.

click here to view table


For results of the soil and protein residue tests as assessment of the mechanical cleaning process, see Table 1 above.

Data shown in Table 1 demonstrate the frequency distribution of the soil and protein residue in the contaminated surgical instruments with the Soil Test and with visual inspection evaluation. The Biotrace Protect and Miele Kit protein residue tests were evaluated by colorimetric comparison. According to the data in Table 1, five of the devices (1.6 percent) evaluated showed a presence of residue in the Soil Test. The absence of Soil Test residue was observed on 308 (98.4 percent) of the devices. The samples totaled 313 devices.

The Soil Test residue was observed on the following instruments: one Ruskin bone-cutting forceps, one Leksell laminectomy rongeur, one Stille-Luer rongeur, one Stille-Liston bone-cutting forceps, and one Kerrison rongeur. In some of the devices, the central joints were disassembled for better access of the mechanical cleaning; however, the design of certain instruments prevented disassembly. The Kerrison and some rongeur models required manual brush cleaning in order to remove internal soil.

With the Biotrace Protect Protein Residue Test, 60 (92 percent) of the devices analyzed showed negative results for the presence of protein. Five (8 percent) of the instruments showed residues in the Soil Test; the Biotrace Protect Protein Residue Test was also applied and the results confirmed the presence of protein.

The Biotrace Protect Protein Residue Test was applied to a device containing organic matter for control purposes; a developing purple color indicated the tests efficacy. The tests carried out with the Miele Protein Test Kit indicated negative results in 141 (100 percent) of the tested devices. The test applied for control purposes to a device with organic matter did not indicate the presence of protein.

In the sample, a total of 514 devices was evaluated. The absence of soil and protein was observed in 509 (98.1 percent) of the devices. In 10 of them (1.9 percent), the presence of soil or protein could have been different if the complex shapes of the devices had been observed and the recommended disassembly and prior manual cleaning had been performed.

The qualification of the thermal washer/disinfector, according to the different BGA, DHSS/HTM, RIVM, SPRI/SIS standards and in cycles with different pasteurization times and temperatures, was conducted by an engineer from a firm specializing in the validation process. The tests were carried out in the cycle, with the washer/disinfector both empty and loaded with devices. According to the protocols, the recommendations and demands from GMP/FDA 21 CFR Part II, GHTF Study Group 3 Quality Systems Process Validation Guide, ISO 15.883:1999 and HTM 2030 were followed, see Table 2 below.

Twelve thermocouples were used and variations among the sensors were less than plus or minus 2 degrees Celsius and in the same sensor less than plus or minus 1 degree Celsius.

These values are inferior to those determined by the ISO 15.883:1999 and HTM 2030 standards. Sensor 7 showed a variation greater than plus or minus 1 degree Celsius in all cycles during the exposition, due to its positioning so close to the water-heating chamber. Consequently, its values were disregarded in the final interpretation of the results. The distribution studies were repeated for each of the aforementioned protocols. No alterations were found to be off from the determined standards, and the cycles were considered as approved.

click here to view table

Data from Table 3 show the importance of the evaluation of all the parameters for DAL and A0, even though the UFC has shown a reduction inferior to less than 102 in all protocols, which does not mean that all protocols were approved, see Table 3 on page 36.

In calculating the theoretical lethality and the DAL, two protocols were approved and five failed because they indicated values smaller than those verified during the thermocouple evaluation. In the evaluation with thermocouples, the protocols approved were: German Standard, BGA time of 10 minutes and temperature of 94 degrees Celsius; British Standard, DHSS/HTM time of 1 second and temperature of 90 degrees Celsius; Dutch Standard, RIVM time of 5 minutes and temperature of 90 degrees Celsius; and the Swedish Standard, SPRI/Sis times of 1 and 3 minutes and temperature of 85 degrees Celsius.

The protocols that failed were: British Standard, DHSS/HTM time of 2 minutes and temperature of 82 degrees Celsius, cycle with 30 minutes and temperature of 70 degrees Celsius used in pasteurizing.


The CS department is one of the most important areas in the hospital environment, and encompasses the management, technical and human resources areas. In the last few years, significant changes have occurred in this field, which are reflected by the performance levels of the professionals who work there and in the new technologies used in cleaning, disinfection and sterilization. (Rutala et al., 2000) CS requires a critical and detailed evaluation of its area, limited by physical barriers, in order to provide a safe work environment. A detailed planning of the accessories, feedstock, instruments and other materials are necessary for surgical planning and for other areas of the healthcare institution.

The cleaning procedures performed in CS must comply with the protocols and guidelines of the manufacturers of the materials and equipment. The cleaning agents must be tested before approval; adequate resources must be provided for the professionals who work in this environment. (Rutala, 2002) The qualification of workers, professional training, and constant evaluation of the knowledge of the protocols and the efficacy of the processes are a high priority. Equipment that operates in a closed system is safer for workers because it reduces the dissemination of contaminants into the environment and reduces the risk of occupational accidents. The use of environment and individual protection equipment should be mandatory. (Fengler, 2001; Schultz, 1997; Spry 2000)

The average viable microbial load found in the instruments analyzed was 108 CFU. The result of the viable microbial load observed after the cleaning and disinfecting process with different time cycles and temperatures for the BGA, DHSS/HTM, RIVM, SPRI/SIS standards and for the pasteurization cycle showed there had been no growth. This result was expressed as less than 102 CFU.

The HTM 2030 and the ISO 15.883-1/1999 standards must be followed in order to validate washer-disinfectors for thermal disinfection.

click here to view table

A validation project to ensure consistent results must be established in compliance with standards. The soil test and protein-residue tests are indicated for the evaluation of thermal disinfection. The standards do not indicate microbial tests for the thermal validation in washer/ disinfectors. The initial CFU result of 108 was used to determine the A0 and DAL values for the theoretical calculations and the verification through the thermocouples during the thermal qualification. The ISO 15.883-1/1999 standard establishes values for the calculation of the A0 and DAL.

For the validation of the thermal qualification for the washer/ disinfector, the tests were conducted following the BGA, DHSS/ HTM, RIVM, and SPRI/SIS standards, and for the cycle with time and temperatures for pasteurization. Twelve thermocouples were used to carry out the thermal distribution study, with three empty cycles and three cycles with instrument loads. All protocols were considered to be approved. The calculations for minimum lethality with thermocouples presented a result higher than those found in the theoretical calculations because the minimum lethality in the thermal validation process starts to accumulate with the increase in temperature, before the beginning of the thermal disinfection phase.

In 1997, Jatzwauk pointed out that measurements with thermocouples can reveal excess or insufficiency in the time-temperature relation. The thermocouples allow for precise measurements, and with results available during and immediately after the validation process. The amount of heat can be directly compared through the value for A and provides technical details of the procedures. An excessive time-temperature relation can be determined in the same way, as well as a totally inadequate heating, according to the ISO.

It is necessary to establish if these theoretical values found are in line with the data obtained in the thermoelectric validation. There are important variables that must be considered in the process, such as: cycle time, temperature, quality and volume of water, types of detergent, dosage, lubricants and the washer model. It is important to obtain this information and detailed evaluation from the manufacturer. To certify these figures, it is important to compare data from the theoretical calculations, thermocouple measurements and microbial count.

By the results achieved in the validation process, the calculation of the minimum lethality and DAL must be studied, evaluated and applied. The estimated time for minimum lethality, according to ISO 15.883-1/1999 and HTM 2030, was 10 minutes. The DAL was calculated based on the initially known population of 108 CFU. To ensure a value for A equal to 10 minutes, a reduction greater than or equal to 102 was needed.

The protocols that achieved the expected minimum lethality and DAL during the thermal qualification with thermocouples were: German Standard, BGA (time of 10 minutes and temperature of 94 degrees Celsius); Dutch Standard, RIVM (time of 5 minutes and temperature of 90 degrees Celsius); Swedish Standard, SPRI/SIS (time of 1 minute and temperature of 85 degrees Celsius); Swedish Standard, SPRI/ SIS (time of 3 minutes and temperature of 85 degrees Celsius); and British Standard, DIHSS/HTM (time of 1 second and temperature of 90 degrees Celsius).

The protocols that did not reach the expected minimum lethality and DAL during the thermal qualification with thermocouples were: cycle time and temperature for pasteurizing (70 degrees Celsius/30 minutes) and British Standard, DHSS/HTM (time of 2 minutes and temperature of 82 degrees Celsius).

The standards of the different countries show that it is possible to reach a reduction in the microbial load of the minimum lethality and DAL above the values found in the theoretical calculations, thus offering a high level of disinfection. The main purpose of this study was achieved, as we now have the information with which we can base our activities aimed at keeping up with technological and scientific evolution in CS, and offering information to the nurses responsible for this department.


This study demonstrates that CS must evolve in its organizational structure. A careful evaluation of the physical area is needed, targeting its overall improvement, installation of adequate resources for the traceability of materials, and the enhancement of environmental and worker safety. Protocols, procedures, and written routines must be validated concerning their applicability, and must be made available in each area. The result must be evaluated with benefits to the patient, assuring that the competency can be demonstrated and the actions performed with quality.

The ISO 15.883-1/1999 and HTM 2030 standards allow for an assessment of the procedures based on scientific research-supported evidence, offering the possibility for the multi-disciplinary team members in the sterilization units to work toward the prevention of infections, to develop new studies, and to apply their experiences to their work environment.


Fengler TW, Pahike H, Bisson S, Michels W. Are processed surgical instruments protein free? Zentr Steril. 2001; 9(1):20-32.

International Standards Organization. Washer-disinfector machines. Geneve: ISO 1999.

Jatzwauk L. Practical testing of thermal disinfection processes using wireless thermologgers. Zentr Steril. 1997; 5(5):260-65.

Michels W. Manual cleaning by immersion method, information on Miele disinfecting appliances. Gutersloh: Miele. 1991. p. 3-13.

NHS States. Executive Agency of the Department of Health. Washerdisinfector: validation and verification. London: The Stationery Office; 1997. (Health Technical Memorandum 2030).

Rutala WA, Weber JD, Gergen MF, Gratta AR. Efficacy of a washer/ pasteurizer for disinfection of respiratory-care equipment. Infect Control Hosp Epidemiol. 2000;21(5):333-6.

Rutala WA, Weber JD, Draft guideline for disinfection and sterilization in healthcare facilities. Atlanta: CDC; 2002.

Schultz JK. Decontamination: recommended practices. In: Reichert M. Sterilization technology for the healthcare facility, 2nd ed.

Gaithersburg; Aspen; 1997. chap. 2, p. 10-20.

Spry C. Renewed interest in instrument cleaning. Surg Serv Manage. 2000; 6(4): 17-20.

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