Evaluation of Cleaning and Disinfection Processes Performed byAutomatic Washer/Disinfectors

May 1, 2005

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

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

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

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

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;

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

Jatzwauk L. Practical testing of thermal disinfection
processes using wireless thermologgers. Zentr Steril. 1997;

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.

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.