Disinfection vs. Sterilization: How to Handle Both

If you're confused about the options available to disinfect or sterilize an item, here's help. In this article, I'll describe the differences between disinfection and sterilization and explain when and where to use each.

Understanding Disinfection
The term disinfection simply means the destruction of harmful microorganisms. As we shall see, the term is relative. You can disinfect a device without destroying all microorganisms on it or even a majority of them.

We classify disinfectants in one of three ways, depending on their relative ability to inactivate different types of microorganisms:

– Low-level disinfectants are effective against only Group A microorganisms, which are the least resistant variety and easiest to inactivate. They include all vegetative bacteria, fungi, and liphophilic viruses (e.g., influenza, HIV, herpes).
– Intermediate-level disinfectants kill both Group A and the slightly more resistant Group B microorganisms, which include M. tuberculosis, HBV, and the hydrophilic viruses (e.g., echovirus and coxsackievirus).
– High-level disinfectants, which include glutaraldehyde, 6% hydrogen peroxide, chlorine dioxide, peracetic acid, and ortho-phthalaldehyde, will destroy Group A, B, and the most resistant C organisms, which include bacterial spores. High-level disinfectants will not kill high numbers of bacterial spores, however. This type of disinfection is often used for endoscopes.

Understanding Sterilization
As opposed to disinfection, sterilization is an absolute term. When you sterilize something, you destroy all forms of microbial life on the item. Something cannot be "partially sterile."

Practically speaking, though, it becomes a matter of probability whether sterility has been achieved. This is expressed as a sterilization assurance level (SAL) measured by the percent reduction or number of logarithmic reductions (D values) brought about by the sterilization process. Before a manufacturer can label a product as sterile, it needs to validate that the process will produce a SAL of 10-6. In other words, it needs to reduce the chances that the item is contaminated to one in 1 million.

When to Use Each Method
It's possible to divide all the items you use in your facility into three categories based on how likely it is that a contaminated item would cause an infection. Here are some examples of items in each category and whether they require disinfection or sterilization:

Critical items enter sterile tissue or come in contact with the vascular system. They include implants and cardiac catheters.

These items pose a high risk of infection if they are contaminated with any microorganism, including bacterial spores. Therefore, they must be sterile prior to use. You have three options for sterilizing these instruments:

1. Steam sterilization: As this is the most effective form of sterilization, use it for all critical items that can withstand the temperatures and pressures of steam sterilization without damage. Contact the manufacturer if there is any question regarding the heat sensitivity of the item or any of its components.

2. Liquid sterilization: If the item cannot withstand high temperatures and is immersible (endoscopes fit in this category) it is possible to use a process such as the Steris System 1?? ? or any other liquid sterilization system that has a proven record of effectiveness and safety. These systems work especially well for lumened instruments, since they force the liquid sterilant through the cannulas. This process is more expensive and somewhat less effective than steam, and it's not possible to package the item prior to sterilization.

3. Gas or plasma. Other low temperature sterilization systems include 100% ethylene oxide (EtO), EtO mixtures, and the Sterrad plasma systems. Any of these methods may be appropriate. EtO and EtO mixtures allow you to package the products prior to sterilization; this gas has excellent penetration. Among the drawbacks are speed; it takes as much as eight hours to sterilize with EtO. This type of system also typically requires exhaust plumbing. The Sterrad system is rapid, sterilizing in 45 to 90 minutes, and there are no fumes, but penetration is not as good as it is with EtO.

If none of these low temperature sterilization methods are available to you, you must either buy single-use, disposable products or contract with one of the sterilization service companies. Semi-critical items come in contact with mucous membranes or non-intact skin. They include respiratory therapy and anesthesia equipment. These items must be free of all microorganisms except for low numbers of bacterial spores. Generally speaking, intact mucous membranes will be resistant to infection by common bacterial spores but may be susceptible to organisms that are relatively easy to kill using high-level disinfection.

If possible, sterilize your semi-critical items, but at a minimum, you need to high-level disinfect them using any of the disinfectants approved by the FDA and/or the EPA for the intended use. High-level disinfectants can even achieve sterility if given enough contact time (hours) and temperature.

When using chemical disinfectants it is critical to ensure that the chemicals are compatible with all parts of the item being disinfected. Some are very corrosive. Be familiar with the OSHA and other safety requirements and pay special attention to the three controlling variables: contact time, temperature and concentration.

Non-critical items come in contact with intact skin but not mucous membranes. They include bedpans, bed rails, blood pressure cuffs, etc. There is little risk of transmitting infectious disease to the patient via these items; however, they can act as a carrier of disease by contaminating the hands of healthcare workers and visitors. Low-level disinfectants like ethyl or isopropyl alcohol, household bleach (1 to 500 dilution), and phenolic, iodophor or quaternary ammonium germicide detergents, are adequate to clean these items.

The Importance of Cleaning
In a device where you can see all the surfaces, you can usually tell if it's clean just by looking at it. This is not true of devices such as endoscopes that draw all sorts of blood, blood products, and other potentially infectious liquids and solids through their cannulas and ports.

Try to clean instruments, especially instruments like endoscopes, right after you use them; if you allow debris to dry within the cannulas it will be almost impossible to get it out. Residual debris will also severely inhibit disinfection or sterilization. Glutaralde-hyde will actually "fix" some debris to the inner walls. Therefore, you should always disassemble the scope and immerse the parts in an enzymatic solution to begin the cleaning process right after use, as difficult as this might be during this very busy time.

Dan Mayworm is the former president of Mayworm Associates, Inc. and publisher of The Journal of Healthcare Resource Management and Infection Control & Sterilization Technology. He is the former president of Tower Products, Inc., a manufacturer of packaging materials for the medical device industry. Mr. Mayworm has served as president of the Health Industries Association and as an executive committee member of the Health Industry Manufacturers Association, and has given expert testimony before both the House and Senate subcommittees.

If you have an infection prevention question that you would like Mr. Mayworm to answer in this column, fax it to 610-240-4919, snail mail it to Outpatient Surgery Magazine, 3 Beryl Road, 2nd Floor, Paoli, PA 19301, or e-mail Mr. Mayworm at [email protected].