Evaluation of Cleaning and Disinfection Processes Performed byAutomatic Washer/Disinfectors


Evaluation of Cleaning and Disinfection Processes Performed byAutomatic Washer/Disinfectors

By Maria Do CarmoNoronha Cominato Bergo, RN, MS


Thermal washer-disinfectors represent a technology thatbrought about great advantages such as the establishment of protocols, standardoperating procedures, and reduction in occupational risk of a biological andenvironmental nature. The efficacy of the cleaning and disinfection obtained byautomatic washer/disinfector machines, in running programs with different timesand temperatures determined by the different official agencies, was validatedaccording to recommendations from International Organization for Standarization(ISO) Standard 15.883-1/1999 and HTM 2O3O (NHS States, 1997) for the determiningof the minimum lethality and disinfection assurance level (DAL), boththeoretically and through the use of thermocouples. In order to determine thecleaning efficacy, the Soil Test, Biotrace Protect and Protein Test Kit wereused. The procedure to verify the colonyforming units (CFU) count of viablemicroorganisms was performed before and after the thermal disinfection. Thisarticle shows that the results are in compliance with ISO and HTM Standards. Thevalidation steps confirmed the high efficacy level of the medical washer/disinfector. This protocol enabled the evaluation of the procedure based onevidence supported by scientific research, and the possibility of developingfurther research.


Currently, there are several large-scale procedures to cleanand disinfect devices used in a hospital environment, hence the need to studythe efficacy of the washer/disinfector. Michels (1991) mentions the concern withthe risk posed by the handling of devices without the use of adequate protectiveequipment and correct standard procedures, as well as the risk of environmentalcontamination from residues generated by the cleaning process. The cleaning ofthe work environment and devices must be perceived as of maximum importance, asincorrect execution triggers serious problems in downstream operations. Cleaningconsists of the manual or mechanical removal of soil deposited on an inertsurface.

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

This investigation was developed to aid the nurses in thecentral supply (CS) department in choosing among the several different programsavailable for the automatic washer/disinfectors, and to provide scientificallysupported procedures. The general objective of this study was to assess theefficacy of the cleaning and disinfection achieved by automaticwasher/disinfector machines in operating programs with different cycle times andtemperatures recommended by different regulatory agencies. The specificobjectives were to assess the efficacy of the disinfection achieved by theautomatic washer/disinfector in operating programs with different cycle timesand temperatures; determine and analyze the lethality rate A0 and DAL in theequipment for the various disinfection programs suggested by differentregulatory agencies in the different countries and comparing the results totheoretical results. (Jatzwauk, 1997)


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

The Miele protein residue test was applied separately in threeconsecutive cycles of mechanical cleaning and 141 devices (47 in each cycle)were evaluated. The choice of the devices was made in accordance to guidelinesfrom the HTM 2030 standard. In this investigation, the thermal qualificationprogram was previously applied in order to assess the efficacy of the medicalwasher/disinfector and the operating programs. The application was done by theengineer responsible for the validation service, with supervision from theinvestigator.

The ISO 15883-1/1999 standard requires that for validationpurposes, the cycles must be performed three consecutive times. Thus, each cyclehad 20 contaminated devices submitted to three cycles for each protocolinvestigated. After the thermal disinfection was completed, the test deviceswere sent to the bromatology and chemistry area in the sterility section of theAdolfo Lutz Institute for identification of the viable microorganisms.

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

After contamination, the excess residue was removed with astream of pressurized cold water and placed between the two and three trays inthe LTD support. The remaining trays were loaded with the contaminated materialin the investigation itself. After the the usual disinfection cycle, gloves andtwo 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.


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

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

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

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

The Biotrace Protect Protein Residue Test was applied to adevice containing organic matter for control purposes; a developing purple colorindicated the tests efficacy. The tests carried out with the Miele ProteinTest 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 notindicate the presence of protein.

In the sample, a total of 514 devices was evaluated. Theabsence 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 proteincould have been different if the complex shapes of the devices had been observedand the recommended disassembly and prior manual cleaning had been performed.

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

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

These values are inferior to those determined by the ISO15.883:1999 and HTM 2030 standards. Sensor 7 showed a variation greater thanplus or minus 1 degree Celsius in all cycles during the exposition, due to itspositioning so close to the water-heating chamber. Consequently, its values weredisregarded in the final interpretation of the results. The distribution studies were repeated for each of theaforementioned protocols. No alterations were found to be off from thedetermined standards, and the cycles were considered as approved.

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

In calculating the theoretical lethality and the DAL, twoprotocols were approved and five failed because they indicated values smallerthan those verified during the thermocouple evaluation. In the evaluation with thermocouples, the protocols approvedwere: German Standard, BGA time of 10 minutes and temperature of 94 degreesCelsius; British Standard, DHSS/HTM time of 1 second and temperature of 90degrees Celsius; Dutch Standard, RIVM time of 5 minutes and temperature of90 degrees Celsius; and the Swedish Standard, SPRI/Sis times of 1 and 3minutes 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 minutesand temperature of 70 degrees Celsius used in pasteurizing.


The CS department is one of the most important areas in thehospital environment, and encompasses the management, technical and humanresources areas. In the last few years, significant changes have occurred inthis field, which are reflected by the performance levels of the professionalswho work there and in the new technologies used in cleaning, disinfection andsterilization. (Rutala et al., 2000) CS requires a critical and detailedevaluation of its area, limited by physical barriers, in order to provide a safework environment. A detailed planning of the accessories, feedstock, instrumentsand other materials are necessary for surgical planning and for other areas ofthe healthcare institution.

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

The average viable microbial load found in the instrumentsanalyzed was 108 CFU. The result of the viable microbial load observed after thecleaning and disinfecting process with different time cycles and temperaturesfor the BGA, DHSS/HTM, RIVM, SPRI/SIS standards and for the pasteurization cycleshowed 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 befollowed in order to validate washer-disinfectors for thermal disinfection.

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. Thestandards 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 DALvalues for the theoretical calculations and the verification through thethermocouples during the thermal qualification. The ISO 15.883-1/1999 standardestablishes values for the calculation of the A0 and DAL.

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

In 1997, Jatzwauk pointed out that measurements withthermocouples can reveal excess or insufficiency in the time-temperaturerelation. The thermocouples allow for precise measurements, and with resultsavailable during and immediately after the validation process. The amount ofheat can be directly compared through the value for A and provides technicaldetails of the procedures. An excessive time-temperature relation can bedetermined in the same way, as well as a totally inadequate heating, accordingto the ISO.

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

By the results achieved in the validation process, thecalculation of the minimum lethality and DAL must be studied, evaluated andapplied. The estimated time for minimum lethality, according to ISO15.883-1/1999 and HTM 2030, was 10 minutes. The DAL was calculated based on theinitially known population of 108 CFU. To ensure a value for A equal to 10minutes, a reduction greater than or equal to 102 was needed.

The protocols that achieved the expected minimum lethality andDAL 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); SwedishStandard, SPRI/SIS (time of 1 minute and temperature of 85 degrees Celsius);Swedish Standard, SPRI/ SIS (time of 3 minutes and temperature of 85 degreesCelsius); and British Standard, DIHSS/HTM (time of 1 second and temperature of90 degrees Celsius).

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

The standards of the different countries show that it ispossible to reach a reduction in the microbial load of the minimum lethality andDAL above the values found in the theoretical calculations, thus offering a highlevel of disinfection. The main purpose of this study was achieved, as we nowhave the information with which we can base our activities aimed at keeping upwith technological and scientific evolution in CS, and offering information tothe nurses responsible for this department.


This study demonstrates that CS must evolve in itsorganizational structure. A careful evaluation of the physical area is needed,targeting its overall improvement, installation of adequate resources for thetraceability of materials, and the enhancement of environmental and workersafety. Protocols, procedures, and written routines must be validated concerningtheir applicability, and must be made available in each area. The result must beevaluated with benefits to the patient, assuring that the competency can bedemonstrated and the actions performed with quality.

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


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

International Standards Organization. Washer-disinfectormachines. Geneve: ISO 1999.

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

Michels W. Manual cleaning by immersion method, information onMiele 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 awasher/ pasteurizer for disinfection of respiratory-care equipment. InfectControl Hosp Epidemiol. 2000;21(5):333-6.

Rutala WA, Weber JD, Draft guideline for disinfection andsterilization 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. SurgServ Manage.2000; 6(4): 17-20.

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