Sterilization - The Ultimate in Clean

Norine McVann
May 1, 2014

Executive Summary

  • “In February (2009), the V[eterans] A[dministration] launched an investigation after learning that more than 10,000 patients at three agency hospitals in the Southeast may have been exposed to HIV, hepatitis and other infections through non-sterile equipment used in colonoscopies or endoscopies conducted as far back as 2003.”1
  • “…A Winston-Salem hospital apologized Monday (February 2014) after improper sterilization exposed nearly 20 patients to a rare neurological disease.”2

Can you imagine learning that the surgical instruments used in your recent medical procedure were contaminated? What a frightening prospect! That is why vigilance around maintaining appropriate levels of sterilization control is so critically important. 

The world is full of microorganisms that can pose a variety of health-related threats to society. To help protect us, various forms of sterilization are used across industries to help reduce, if not eliminate, our exposure to these hazards. The Food and Drug Administration specifically mandates the use of sterilization in the food and medical products industries through the Code of Federal Regulation, Part 820 Quality System Regulation. These mandates require the validation of the sterilization process and verification that confirms the sterilization has been successfully fulfilled.3

Sterilization Defined

The formal definition of sterilization is “the process of destroying all microorganisms and their pathogenic products.”4 The aim of sterilization is the reduction of bioburden (microorganisms or potential pathogens) that could lead to illness and infection as the result of contact with these pathogens on the products we encounter - whether they are food, medicine or medical instruments.

Methods of Sterilization

The sterilization process can be accomplished through a variety of means such as heat, radiation and the use of chemicals.5 The following lists the various options available today, describing the process, features and caveats.

  • Heat: Heat is used in a variety of ways to sterilize products including moist steam, dry heat, flaming and incineration.
    • Moist Steam - a widely used method for heat sterilization using a device called an autoclave. Autoclaves commonly use steam at temperatures of 121-134 C (250F-273F) and sterilizes equipment and supplies by subjecting them to high-pressure, saturated steam for 15–20 minutes, depending on the size of the load and the contents. Autoclaves are widely used in the microbiology, medical, veterinary science, dentistry and prosthetics industries to name a few. Autoclave treatment will inactivate fungi, bacteria, viruses and bacterial spores when properly administered. These devices come in a variety of sizes ranging from desktop to large standalone units.   
    • Dry Heat - This process is accomplished by conduction, whereby heat is absorbed by the exterior surface of an item and then passed inward to the next layer. Eventually, the entire item reaches the proper temperature needed to achieve sterilization. As heat takes much longer to be transferred to the product using this method, both the duration and the temperature are usually increased, unless forced ventilation of hot air is used. However, dry heat has the advantage that it can be used on powders such as pharmaceutical materials and other heat-stable items that would be adversely affected by moist steam.
      Instruments should be dry before sterilization since water will interfere with the process. Dry-heat destroys microorganisms by causing coagulation of proteins.
    • Flaming - used in microbiology labs whereby a Bunsen burner or alcohol lamp heats a surface to a red glow to inactivate any infectious agent. This is commonly used for small metal or glass objects.
    • Incineration - commonly used to sanitize medical waste and other biohazardous materials by reducing it to ash. This would be used to prevent microbial contamination when product is being disposed with other non-hazard waste products.
  • Chemical Sterilization:  Although heat provides the most reliable method of sterilization, it can damage heat-sensitive materials such as plastics, electronics and fiber optics. For such materials, sterilization through the use of gases such ethylene oxide and chemical-oxidizing agents such as hydrogen peroxide and ozone may be the best alternative. However, it is important that materials being sterilized through these methods are chemically compatible with the sterilant being used to prevent damage to the product itself.
    • Ethylene Oxide (EtO) - commonly used chemical method penetrates well through paper, cloth and plastic films and kills known viruses, bacteria and fungi and is compatible with most materials. It is widely used in medical device manufacturing as a large-scale sterilization process. More than 50 percent of disposable medical devices are sterilized using this method. However, it is also highly flammable, toxic and carcinogenic with the potential to cause reproductive damage, so operating controls are critical. 
    • Ozone - used in industrial settings to sterilize water and air. The benefit is that it is able to oxidize most organic matter. However, this gas is toxic and unstable limiting its use in many cases.
    • Bleach - will kill many organisms but not all spores; it is also highly corrosive. 
    • Formaldehyde - an acceptable liquid chemical agent if the device is properly immersed for a sufficient length of time.  It can also be used as a gaseous agent and is used in this form to sterilize vaccines. 
    • Hydrogen peroxide - a strong oxidant effective against a wide range of microorganisms, including bacteria, yeasts, fungi, viruses and spores. Hydrogen peroxide is a stable and effective means of microbial sterilization when used on surfaces. It has been used on products such as soft contact lenses, ventilators, fabrics and endoscopes.6
  • Radiation Sterilization:  This process involves the use of ionizing and non-ionizing radiation to sterilize products.  Gamma, E-beam and X-rays are forms of ionizing radiation while UV light is a form of non-ionizing radiation. Radiation sterilization causes damage to organism cell chromosomes or DNA. Damaged cell DNA cannot reproduce or function properly leading to death of the microbial.7
      • Electron beam (E-Beam) - uses an on-off technology and creates a higher dosing rate that requires a lower exposure time, reducing decomposition of materials such as polymers in the product being sterilized. This method of sterilization is often used with disposable medical devices. Facilities that use this sterilization process require substantial concrete shielding to protect both the environment and workers from radiation exposure.
      • X-ray - in the high energy form it can irradiate large packages and pallet loads of medical devices. Their penetration is sufficient to treat multiple pallet loads with good uniformity.  X-ray sterilization is an electricity-based process not requiring chemical or radioactive material.9
        Below is an illustration10 of the different radiation technologies noted above and their penetrating properties.

     

    • Ultraviolet Light – a non-ionizing form of sterilization with limited use as it is only capable of sterilizing surfaces and some transparent objects. UV irradiation uses short light waves to kill microorganisms by destroying the nucleus and preventing cell function. The effectiveness of this method depends on “line of sight” of the UV light source to the microorganism. If the UV light is obstructed the sterilization is ineffective.11 It is routinely used to sterilize the interiors of biological safety cabinets between uses, but is ineffective in shaded areas, including areas under dirt. It also damages some plastics, such as polystyrene foam if exposed for prolonged periods of time.

Each of the radiation sterilization methods noted above has its limitations, so choosing the correct method will help ensure the validation of the sterilization as mandated by governing agencies.

Sterilization Process Monitoring

Sterilization procedures should be monitored through a combination of mechanical, chemical and biological techniques designed to evaluate the sterilizing conditions and the procedure's effectiveness.12

  • Mechanical –includes techniques for monitoring sterilization equipment such as the cycle time, temperature and pressure by observing gauges or displays on the sterilizer. Correct readings do not ensure sterilization, but incorrect readings could be the first indication that a problem has occurred with the sterilization cycle.
  • Chemical Indicators (CIs) - internal and external, use-sensitive chemicals that assess physical conditions such as temperature or sterilant penetration during the sterilization process. Chemical indicators such as heat-sensitive tape change color when a given dose is reached. An internal chemical indicator should be placed in every package to ensure the sterilization agent has penetrated the packaging material and actually reached the instruments. 
    CI test results can be viewed immediately after the sterilization cycle is complete and could provide an early indication if a problem occurred during the process. Because chemical indicators do not prove sterilization has been achieved, a biological indicator (i.e., spore test) is required.
  • Biological indicators (BIs) - considered the most accepted means of monitoring the sterilization process by the Center for Disease Control.  This is because they directly determine whether the most resistant microorganisms (e.g., Geobacillus or Bacillus species) are present, rather than merely indicating whether the physical and chemical conditions necessary for sterilization have been met.13  In addition, the placement of the BIs within the sterilizer should follow the manufactures instruction for use.14

The Center for Disease Control requires that any load containing implantable devices be monitored, and that each sterilizer be tested at least weekly through the use of BIs to verify the units are functioning correctly.15

Once the sterilization cycle has been completed, the load should be protected and handled in a way that will maintain the sterility of the product.16 In addition, manufacturer’s instructions on proper installation and equipment maintenance should be followed for all sterilization equipment.17

The location of microorganisms on a product is a critical factor that must be assessed to ensure that the appropriate sterilization method is being used.  Medical instruments with multiple pieces must be disassembled and equipment such as endoscopes that have crevices, joints and channels are more difficult to access than are flat-surface equipment. This is because it is difficult for the sterilization process to penetrate all parts of the equipment. Only surfaces that directly contact the sterilant will actually be sterilized, so there must be no air pockets and the equipment must be completely immersed for the entire exposure period. Given this challenge, manufacturers should be encouraged to produce equipment that is easy to sterilize and clean.18

SAL

Once the sterilization process is completed, it must be verified. This verification is conducted through the use of a mathematical process called Sterility Assurance Level (SAL) to determine the probability that a given process has made something sterile. A level of 10−6 is recommended for organisms on a sterilized device.19 This is essentially saying that there is a less than or equal to one chance in a million that an item remains contaminated and is therefore not sterile.20

  • 10-3 – Required for products not intended to come into contact with breached skin or compromised tissue. This includes topical devices (gowns, ECG electrodes, etc.), urinary catheters, tongue depressors, etc.21
  • 10-6 – Required for products intended to come into contact with breached skin or compromised tissue.  It includes implantables and products that are invasive such as wound dressings and hypodermic needles, as well as products that claim sterile fluid pathways (i.e. IV sets, syringes, etc.)

Contract Sterilization Firms & Standards

There are numerous firms globally that provide contract sterilization services. Two of the largest and most recognized names in the contract sterilization business are Steris and Sterigenics International, Inc. Contract sterilizers should be compliant with the FDA’s 21 CFR 820 for quality systems along with ISO 13485. They should also be in compliance with various standards (ANSI, AAMI and ISO) governing sterilization methods as noted:

  • ANSI/AAMI/ISO 11135:2007 – Sterilization using Ethylene Oxide (EO)
  • ANSI/AAMI/ISO 11137:2006 – Sterilization using Radiation
  • ANSI/AAMI/ISO 17665:2006 – Sterilization using Moist Heat
  • ANSI/AAMI/ISO 20857:2010 – Sterilization using Dry Heat

Contractual Controls

Any companies using contract sterilization firms should implement the practice of formal contracts with a statement outlining the role and responsibility of both parties. These contracts should have legal review and include insurance requirements as a means of providing financial protections to the manufacturer. The collection and retention of sterility certificates is also important in tracking products for recall purposes once it is released to the market. The ability to retrieve products that are believed to be contaminated is critical in protecting the end user from possible injury or illness. 

Conclusion

There will always be a need for sterilization to protect the public from harmful microorganisms. Ensuring sterilization procedures are properly implemented and verifiable is also critical as many of the sterilization processes are themselves potentially harmful, not only to the end product but to those working with the various sterilization techniques. The total elimination of harmful microorganisms is simply not possible. However, the science and technologies used to measure the success of sterilization techniques, along with the governing regulatory requirements, have created a system that, has served well in protecting the public from unseen harm.

Contact Us

To learn more about how OneBeacon Technology Insurance can help you manage online and other technology risks, please contact Dan Bauman, Vice President of Risk Control for OneBeacon Technology Insurance at dbauman@onebeacontech.com or 262.966.2739.

References

1 Mundell, E. J. (June 16, 2009). “VA faces questions over tainted colonoscopies.”  US News.  Retrieved April 2014.  http://health.usnews.com/health-news/family-health/cancer/articles/2009/06/16/va-faces-questions-over-tainted-colonoscopies

Associated Press (February 11, 2014).  “20 exposed to incurable brain disease in N.C. hospital” Retrieved April 2014. http://www.usatoday.com/story/news/nation/2014/02/11/creutzfeldt-jakob-exposure/5389547/           

USFDA, CFR 21, Part 820 Quality System Regulation.  Retrieved February 2014. http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=820&showFR=1&subpartNode=21:8.0.1.1.12.2

4  The Free Dictionary, Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition.  Retrieved February 2014. http://medical-dictionary.thefreedictionary.com/sterilization

5 The International Pharmacopoeia, Fourth Edition, 3rd Supplement, 2013, Section 5.8 – Methods of Sterilization. Retrieved February 2014.  http://apps.who.int/phint/en/p/docf/

CDC, Guidelines for Disinfection and Sterilization in Health Care Facilities, 2008.  Retrieved February 2014. http://www.cdc.gov/hicpac/disinfection_sterilization/7_0formaldehyde.html

7 How is Radiation used to sterilize medical instruments?  Health Physics Society.  Retrieved February 2014.  http://hps.org/publicinformation/ate/q4004.html

8 “Gamma Processing.” Synergy Health.  Retrieved February 2014.  http://www.synergyhealthplc.com/sites/default/files/synergy-health-sterilisation-specialist.pdf

9 “X-Ray Sterilization of Medical Devices.” MedicalDevice-Network.com. Retrieved February 2014. http://www.medicaldevice-network.com/projects/x-ray-sterilization/

10 Image of Ionization Sterilization and penetration distances. http://en.wikipedia.org/wiki/Sterilization_(microbiology)

11 Ultraviolet germicidal irradiation http://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiation

12 CDC, FAQ on Sterilization-Monitoring. Retrieved February 2014. http://www.cdc.gov/OralHealth/infectioncontrol/faq/sterilization_monitoring.htm#a1

13 Ibid 12

14 Ibid 12

15 Ibid 12

16 “The Standard for Cleaning, Disinfection and Sterilization of Reusable Medical Devices for Health Care Facilities and Settings.” (June 2012). Alberta Government.  Retrieved February 2014. Section 7.4, page 20. http://www.health.alberta.ca/documents/IPC-Medical-Device-Cleaning-2012.pdf

17 Ibid 16, page 21.

18 Rutala, William; Weber, David (November 2008). “CDC Guideline for Disinfection and Sterilization in Healthcare Facilities.”  Retrieved February 2014 http://www.cdc.gov/hicpac/Disinfection_Sterilization/4_0efficacyDS.html

19 Ibid 4 

20 “Sterility Assurance Compliance- A Guide for Medical Device Manufactures.” Northview Biosciences, Inc. Retrieved February 2014. http://hbehcan.tripod.com/dosyalar/mak.pdf

21 “Sterility Assurance Levels (SAL).”  Steris Isomedix.  (September 2007), Retrieved February 2014. http://www.isomedix.com/wp-content/uploads/2013/03/19-Sterility-Assurance-Levels-SALs-Irradiation.pdf

OTHER SOURCES:

http://www-naweb.iaea.org/napc/iachem/Brochgammairradd.pdf
http://npic.orst.edu/factsheets/antimicrobials.html