Low-Temperature Sterilization: Characteristics, Benefits, Monitoring

William A. Rutala, PhD, MPHDirector, Hospital Epidemiology, Occupational Health

and Safety at UNC Health Care System; Professor of Medicine and Director, Statewide Program for

Infection Control and Epidemiology at University of North Carolina at Chapel Hill, USA

Disclosure-3M

Low-Temperature Sterilization

Provide overview of low-temperature sterilizationCharacteristicsBenefits Monitoring

www.disinfectionandsterilization.org

Disinfection and Sterilization in Healthcare FacilitiesWA Rutala, DJ Weber, and HICPAC, www.cdc.gov

Overview Last Centers for Disease Control and Prevention guideline

in 1985 158 pages (>82 pages preamble, 34 pages

recommendations, glossary of terms, tables/figures, >1000 references)

Evidence-based guideline Cleared by HICPAC February 2003; delayed by FDA Published in November 2008

Disinfection and Sterilization EH Spaulding believed that how an object will be disinfected

depended on the object’s intended use.CRITICAL - objects which enter normally sterile tissue or the

vascular system or through which blood flows should be sterile.

SEMICRITICAL - objects that touch mucous membranes or skin that is not intact require a disinfection process (high-level disinfection [HLD]) that kills all microorganisms but high numbers of bacterial spores.

NONCRITICAL -objects that touch only intact skin require low-level disinfection (or non-germicidal detergent).

Efficacy of Sterilization Influencing Factors

Cleaning of the objectOrganic and inorganic load presentType and level of microbial contaminationConcentration of and exposure time to disinfectant/sterilantNature of the objectTemperature and relative humidity

Processing “Critical” Patient Care ObjectsClassification: Critical objects enter normally sterile tissue or

vascular system, or through which blood flows.

Object: Sterility.Level germicidal action: Kill all microorganisms, including bacterial

spores.Examples: Surgical instruments and devices; cardiac

catheters; implants; etc.Method: Steam, gas, hydrogen peroxide gas plasma,

vaporized hydrogen peroxide, ozone or chemical sterilization.

Critical ObjectsSurgical instrumentsCardiac catheters Implants

SterilizationThe complete elimination or destruction of all forms of microbial life and is accomplished in healthcare facilities by either physical or chemical processes

Sterilization of Patient Equipment

Alternatives to ETO-CFCETO-CO2, ETO-HCFC, 100% ETO

Newer Low Temperature Sterilization TechnologyHydrogen Peroxide Gas PlasmaVaporized hydrogen peroxideOzone-not commonly used

Cleaning Mechanical cleaning machines-automated equipment may

increase productivity, improve cleaning effectiveness, and decrease worker exposure Utensil washer-sanitizer Ultrasonic cleaner Washer sterilizer Dishwasher Washer disinfector

Manual

STERILIZATIONFactors affecting the efficacy of sterilization Bioburden Cleaning Pathogen type Protein and salt Biofilm accumulation Lumen length and diameter Restricted flow

Lumens Sterilized by VariousLow-Temperature Sterilization Methods

Challenge: 12/88 100%ETO HCFC-ETO Sterrad10% Serum,0.65% Salt(7 organisms, N=63) 44% 39.7% 49.2% 35%No Serum or Salt,(3 organisms, N=27) ND 96.3% 96.3% NDAlfa et al. Infect Cont Hosp Epidemiol 1996;17:92-100. The three organisms included: E. faecalis, M.

chelonei, B. subtilis spores. The seven organisms included: E. faecalis, P. aeruginosa, E.coli, M. chelonei, B. subtilis spores, B. stearothermophilus spores, B. circulans spores

Low-Temperature Sterilization Technologies (LTST)Conclusions

All LTST technologies have limitations LTST (ETO, HP gas plasma) demonstrate a significant

number of failures in presence of serum or salt Salt and serum provide protection for spores and

bacteria Salt and serum combined with a narrow lumen provide

extraordinary protection with LTST

IS THERE A STANDARD TO DEFINE WHEN A DEVICE IS CLEAN?

There is currently no standard to define when a device is “clean”, cleanliness controlled by visual

Potential methods: level of detectable bacteria; protein (6µg/cm2); endotoxin; ATP; lipid

This is due in part to the fact that no universally accepted test soils to evaluate cleaning efficiency and no standard procedure for measuring cleaning efficiency

At a minimum, a cleaning process should: reduce the natural bioburden; remove organic/inorganic contaminants; provide devices that when sterilized have a SAL 10-6

Verifying Cleaning Processes AAMI recommends incorporating test methods that verify

the functionality of the automated washer Washer indicators have been in use in Europe and

Canada and some US hospitals Washer indicators are chemical indicators imprinted with a

dried test soil formula and a dye.

Cleaning Indicators for Washers Monitor the automated

washer and instrument cleaning chemistry functionaiity

Indicator includes proteins, lipids, and polysaccharides to mimic common challenging test soils

Low-Temperature Sterilization Provide overview of low-temperature sterilization

Characteristics Benefits-sterilize temperature and moisture-sensitive

medical and surgical devices in health care Review advantages/disadvantages of LTS technology

Monitoring

100% Ethylene Oxide4.8 ft3 chamber

Ethylene Oxide (ETO) Advantages

Very effective at killing microorganisms Penetrates medical packaging and many plastics Compatible with most medical materials Cycle easy to control and monitor

Disadvantages Some states (CA, NY, TX) require ETO emission reduction of 90-

99.9% (air pollution control device) CFC (inert gas that eliminates explosion hazard) banned after 1995 Potential hazard to patients and staff Lengthy cycle/aeration time

Ethylene Oxide Aeration• The ability to penetrate is an important characteristic of

ETO• It is this property that necessitates extended periods of aeration

• During aeration, heated air is flushed through chamber to remove ETO residuals from sterilized items

• Consult the medical device manufacturer for recommended aeration times• Composition of device

• Intended application

Aeration Time Guidelines*

Temperature Aeration Time

50°C 12 hours

60°C 8 hours

* Based on polyvinylchloride (PVC) tubing

Ref: ANSI/AAMI ST41:2008 Section 8.8.4

Ethylene Oxide Aeration

OSHA Occupational Exposure Standard for ETOExposure Limits

Employer required to monitoremployee exposure WHAT?

• Monitor for 8-hour TWA

• 15 minute sampling period

HOW?• Breathing zone air samples

WHO?• Representative employee on each shift for each job classification

If ETO exposure 0.5 ppm Action Level, 8-hr TWA-monitoring of those employees can be discontinued

3M™ Ethylene Oxide Monitor 3550

Hydrogen Peroxide Gas Plasma

Hydrogen Peroxide Gas Plasma Sterilization

Advantages Safe for the environment and health care worker; it leaves

no toxic residuals Fast - cycle time is 28-52 min and no aeration necessary Used for heat and moisture sensitive items since process

temperature 50oC Simple to operate, install, and monitor Compatible with most medical devices

Hydrogen Peroxide Gas Plasma Sterilization

Disadvantages Cellulose (paper), linens and liquids cannot be processed Sterilization chamber , about 3.5ft3 to 7.3ft3

Endoscopes or medical devices restrictions based on lumen internal diameter and length (see manufacturer’s recommendations); expanded claims with NX

Requires synthetic packaging (polypropylene) and special container tray

V-PRO™1, Vaporized Hydrogen Peroxide Advantages

Safe for the environment and health care worker; it leaves no toxic residuals

Fast - cycle time is 55 min and no aeration necessary Used for heat and moisture sensitive items (metal and nonmetal devices)

Disadvantages Sterilization chamber is small, about 4.8ft3

Medical devices restrictions based on lumen internal diameter and length-see manufacturer’s recommendations, e.g., SS lumen 1mm diameter, 125mm length

Not used for liquid, linens, powders, or any cellulose materials Requires synthetic packaging (polypropylene) Limited use and limited comparative microbicidal efficacy data

Ozone Advantages

Used for moisture and heat-sensitive items Ozone generated from oxygen and water (oxidizing) No aeration because no toxic by-products FDA cleared for metal and plastic surgical instruments, including

some instruments with lumens Disadvantages

Sterilization chamber small, 4ft3

Limited use (material compatibility/penetrability/organic material resistance?) and limited microbicidal efficacy data

ConclusionsSterilization

All sterilization processes effective in killing spores Cleaning removes salts and proteins and must precede

sterilization Failure to clean or ensure exposure of microorganisms

to sterilant (e.g. connectors) could affect effectiveness of sterilization process

RecommendationsMethods of Sterilization

Steam is preferred for critical items not damaged by heat Follow the operating parameters recommended by the

manufacturer (times, temperatures, gas conc) Use low temperature sterilization technologies for

reprocessing critical items damaged by heat Aerate surgical and medical items that have been

sterilized in the ETO sterilizer

Newer Trends in Sterilization of Patient Equipment

Alternatives to ETO-CFCETO-CO2, ETO-HCFC, 100% ETO

New Low Temperature Sterilization Technology

Hydrogen peroxide gas plasma-most common

Vaporized hydrogen peroxide-limited clinical useOzone and hydrogen peroxide-not FDA cleared

Nitrogen dioxide-not FDA cleared

Low-Temperature Sterilization Provide overview of low-temperature sterilization

Characteristics Benefits-sterilize temperature and moisture-sensitive

medical and surgical devices in health care Monitoring

Monitoring of Sterilizers Use physical, chemical and biological monitors to ensure the

effectiveness of the sterilization process Each load should be monitored with physical and chemical

indicators If the physical, chemical or biological indicators suggest

inadequate processing, the items should not be used Biological indicators should be used at least weekly (commonly

daily or each load) with spores intended specifically for the type of sterilizer

Objectives of Monitoring the Sterilization Process

Assures probability of absence of all living organisms on medical devices being processed

Detect failures as soon as possibleRemoves medical device involved in failures

before patient use

Sterilization MonitoringSterilization monitored routinely by combination of physical,

chemical, and biological parameters Physical - cycle time, temperature, pressure Chemical - heat or chemical sensitive inks that change

color when germicidal-related parameters present (Class 1-6)

Biological - Bacillus spores that directly measure sterilization

Biological Indicators • Select BIs that contain spores of

Bacillus atrophaeus

• Rationale: BIs are the onlysterilization process monitoringdevice that provide a direct measure of the lethality of the process

Biological Monitors ETO - B. atrophaeus New low temperature sterilization technologies

HP gas plasma (Sterrad) and HP vapor (V-Pro)- G. stearothermophilus

Ozone-G. stearothermophilus

Process Challenge Device (PCD)

“A PCD is a device used to assess the effective performance of a sterilization process by providing a challenge to the process that is equal or greater than the challenge posed by the most difficult item routinely processed.”

•PCD may be:

• User-assembled test pack

• Commercially available, FDA cleared preassembled test pack

•ST41 describes two types of PCDs

• Routine BI test pack

• Challenge BI test pack

Ethylene Oxide Sterilization Recommended Monitoring Practices

ANSI/AAMI ST41:2008, Section 10

Routine Load Release/Sterilizer Efficacy Monitoring

• Physical monitoring of cycle• External and internal monitoring of packages• Monitoring of every load with a PCD (routine test pack) containing a BI and a CI or equivalent, commercially available BI PCD

• Ideally, quarantine implants until BI results are known

Ethylene Oxide

BI placed in full load in center

Frequency, in each load Visual, color 48 hour

readout Rapid readout BI for ETO

provides 4hr (not shown)

Hydrogen Peroxide Gas Plasma

Provides evidence that proper sterilization conditions were achieved in 24 hours

Built-in chemical indicator confirms it has been exposed to HP if color changed from red to yellow

Placed in peel pack on bottom rack with tyvek side up 1x per day

CI placed in every load

Monitoring of Sterilizers

Internal Chemical IndicatorValidates the sterilant penetrated the pack or trayAdvantage of the pack control monitor is that it is

inside each pack in multiple locationsDetect local problem

RecommendationsMonitoring of Sterilizers

Following a single positive biological indicator used with a method other than steam, treat as non-sterile all items that have been processed in that sterilizer, dating back to last negative biological indicator. These non-sterile items should be retrieved, if possible, and reprocessed.

Routine Load Release/Routine Sterilizer Efficacy Monitoring

Acceptance criteria• Appropriate readings from physical monitors

• Appropriate readings from CIs

• Negative result from BI in PCD

• Positive BI control result

• Run a control BI, with matching lot #, each day

• Document all results in sterilization cycle record

ANSI/AAMI ST41:2008, Section 10

RecommendationsStorage of Sterile Items

Sterile storage area should be well-ventilated area that provides protection against dust, moisture, and temperature and humidity extremes.

Sterile items should be stored so that packaging is not compromised

Sterilized items should be labeled with a load number that indicates the sterilizer used, the cycle or load number, the date of sterilization, and the expiration date (if applicable)

Conclusions All sterilization processes effective in killing spores Cleaning removes salts and proteins and must precede

sterilization Delivery of sterile products for use in patient care

depends not only on the effectiveness of the sterilization process but also on cleaning, disassembling and packaging of the device, loading the sterilizer, and monitoring

Low-Temperature Sterilization Provide overview of low-temperature sterilization

Characteristics Benefits Monitoring

References Rutala WA, Weber DJ. Disinfection and sterilization: What clinicians need

to know. Clin Infect Dis 2004;39:702 Rutala WA, Weber DJ, HICPAC. CDC guideline for disinfection and

sterilization in healthcare facilities. November 2008. www.cdc.gov Alfa MJ, Olson N, DeGagne P, Hizon R. New low temperature sterilization

technologies: Microbicidal activity and clinical efficiency. In Rutala WA, ed. Disinfection, Sterilization, and Antisepsis in Healthcare. Champlain, NY: Polyscience Publications. 1998:67-78.

Rutala WA, Weber DJ. Clinical effectiveness of low-temperature sterilization technologies. Infect Control Hosp Epidemiol 1998;19:798-804.

Rutala WA, Weber DJ. Disinfection and sterilization. 2013;41:S2