by Susan Cantrell

Much of the literature on disinfectants and sterilants opens with a definition of terms. Which indicates that the subject is not a simple one, although it can be understood with a little effort. William A. Rutala, PhD, MPH, University of North Carolina at Chapel Hill, a world-renowned expert on the subject, describes sterilization as "the complete elimination or destruction of all forms of microbial life, required for instruments or devices that have contact with sterile tissue. Disinfection describes a process that eliminates many or all pathogenic microorganisms on inanimate objects with the exception of bacterial spores." Therefore, chemicals that eliminate all microbial life, including spores, are referred to as sterilants, whereas disinfectants eliminate all or most pathogenic organisms but not spores.

The importance of pre-cleaning

Before objects are disinfected or sterilized, they must be rendered safe to handle, so first they must be decontaminated. In fact, the most important step toward disinfection or sterilization is a thorough cleaning of the objects. And while cleaning does help to reduce the microbial load, its real purpose is to remove soil such as blood, pus, or mucous that would interfere with the disinfectant or sterilant in doing its job by blocking direct contact to the object.

"Cleaning is the removal of foreign material (eg, soil and organic material) from objects," Rutala told HPN, "and it is normally accomplished using water with detergents or enzymatic products. Thorough cleaning is required before high-level disinfection and sterilization since inorganic and organic materials that remain on the surfaces of instruments interfere with the effectiveness of these processes."

"The most oft-repeated phrase in the industry," said Jack Kinville, Marketing Manager, Ruhof Corporation, Mineola, NY, "is ‘If it’s not clean, you can’t sterilize it’." That sounds a little funny, but it’s really very serious. Kinville explains why: "As long as there is bioburden on an instrument, no matter how miniscule, the instrument is unsafe to use and can cause cross-contamination."

Bioburden that is not cleaned from instruments before disinfection or sterilization can translate to added costs due to cross-contamination, which can lead to lengthier hospital stays and further treatments for patients, but it also can shorten the life of the instrument unnecessarily, causing the need for repairs or early replacement. Kinville expounded: "Residual bioburden can cause harmful corrosion, rusting, and pitting, reducing the life of the instrument. That is why it is important to have a synergistic blend of enzymes to remove all bioburden (blood, fat, carbohydrates, starch, and protein). If you have an enzymatic cleaner containing only a protein enzyme, you are not going to be able to remove fat, carbohydrates, or starch; so, you must have a specific enzyme to remove each individual contaminant: carbohydrase for carbohydrates, amylase for starch, protease for blood and protein, and lipase for fat."

Desirable attributes of cleaning solutions

Kinville summed up qualities important in cleaning solutions. A good cleaning solution should make it possible to

• Use only one cleaner for every department, to reduce inventory

• Use a cleaner with a built-in detergent, to eliminate the need to buy separate detergents

• Remove all bioburden, to lower instrument repair and replacement costs

• Speed up instrument turnaround time; no bioburden on instruments means no rewashing

• Reduce the risk of cross-contamination, raising the level of patient safety

• Have low-sudsing, for better visibility of instruments as they are being cleaned

• Be used on all instruments and scopes

• Be used in all automatic washers, washer sterilizers, and ultrasonic equipment, and for manual cleaning

• Remove all blood, fat, carbohydrates, starches, and protein

• Be neutral pH, safe for use on all scopes and instruments

Classification system

In 1968, Earle H. Spaulding devised a classification system for items that need to be disinfected or sterilized for reuse. With a little tweaking, it’s basically still used today by infection control practitioners. Spaulding’s system divided instruments and other items used on or by patients into three categories: critical, semicritical, and noncritical.1,2

Critical items are those that would present a high risk of infection if they were contaminated with infectious microorganisms or spores. This category includes surgical instruments, cardiac and urinary catheters, and implants, objects that invade sterile tissue or the vascular system.1,2 Critical items must be sterilized, because sterile tissue absolutely should come in contact only with sterile instruments.

Semicritical objects are those that touch mucous membranes or skin whose integrity has been breached. Included in this category are items such as respiratory therapy and anesthesia equipment, hydrotherapy tanks, and endocavitary probes.1,2 Rutala notes that, "High-level disinfection is required for semicritical items, such as endoscopes, that come in contact with mucous membranes or non-intact skin."

Noncritical items include equipment such as blood pressure cuffs, bed rails, linens, bedside tables, furniture, and floors.1,2 "Low-level disinfection is recommended for noncritical items that come in contact with intact skin. Intact skin acts as an effective barrier to most microorganisms; therefore, the sterility of items coming in contact with intact skin is ‘not critical’," explained Rutala. (It should be noted, however, that noncritical items could cause secondary transmission, because infectious microorganisms on them can be transmitted to the patient by, for example, the hands of healthcare workers who have handled the contaminated object.)1

Factors to consider when choosing disinfectants

The Table shows a breakdown of disinfectants and sterilants used in each of the three categories, critical, semicritical, or noncritical.1 Disinfectants and sterilants should be selected carefully, with consideration given to the type of material out of which the instrument or item to be disinfected or sterilized is made. For instance, heat is one of the suggestions for sterilizing critical items, but the item must be able to tolerate the heat or it could be ruined. Stabilized hydrogen peroxide and sodium hypochlorite are two chemicals recommended for semicritical devices requiring high-level disinfection, but they can harm some metals. Clearly, it’s important to have a knowledge of which chemicals are appropriate to use on which materials. Manufacturer’s recommendations must be given serious consideration, too.

Some of the chemicals cross categories, the difference being the level of disinfection, which is determined by the length of time the object is exposed to the chemical. For example, some disinfectants will kill spores, sterilizing objects, if the objects are exposed to the chemicals for an extended period of time (6 to 10 hours).1,2 These same disinfectants, at different concentrations and at shorter periods of exposure, will perform high-level disinfection by killing all microorganisms except high numbers of bacterial spores.1,2 Which disinfectant is chosen, the concentration of the disinfectant, and the exposure time is determined by the risk of infection posed with the use of the instrument or item.2

Properties of ideal disinfectants

Properties to look for when selecting the ideal disinfectants were outlined by Rutala. Disinfectants should

• Be a broad-spectrum antimicrobial

• Be fast-acting

• Be unaffected by environmental factors

• Be nontoxic

• Be surface-compatible so that it doesn’t cause corroding or deterioration

• Be easy to use

• Be odorless

• Be economical

• Be water-soluble

• Be stable in concentrate and use-dilution

• Have good cleaning properties

• Be nonflammable

• Leave a residual effect on the treated surface

An interesting point is that certain organisms seem to have a built-in resistance to certain disinfectants.1 The concentration of the chemical can make a difference in the organisms’ susceptibility to the disinfectant.1

There’s a great deal about which one must be educated when in charge of choosing chemicals and methods used to sterilize or disinfect items reused on or by patients, much that’s really important to understand before it’s possible to make informed and responsible choices. But there is one thing that isn’t understood, and, oddly enough, that’s how sterilants and disinfectants work. "The mechanisms by which germicides inactivate microorganisms remain incompletely understood," said Rutala. "Unlike antibiotics, most disinfectants have multiple target sites of action to include the cell wall, cytoplasmic membranes, cytoplasmic constituents (eg, nucleic acids, ribosomes, etc)."

Well, we can live without complete knowledge of how disinfectants work; fortunately, strict adherence to using them properly makes just exactly that possible for many people each day. HPN

REFERENCES

1.Rutala WA. Selection and use of disinfectants in health care. In: Mayhall CG. Hospital Epidemiology and Infection Control. 1st ed. Baltimore, MD: Williams & Wilkins; 1996:913-936.

2.Rutala WA. Disinfection and sterilization of patient care items. In: Herwaldt LA, Decker MD. A Practical Handbook for Hospital Epidemiologists. 1st ed. Thorofare, NJ: SLACK Inc; 1998:271-280.