Disinfection is confusing because of the many products available and because of the differences in opinion about which types of disinfectants should be used.
Chris Miller, PhD
A high-level disinfectant is sporicidal and also will kill hydrophilic viruses if used at the appropriate contact time within the stated use-life. Most everyone in hygiene and dentistry has seen all of these terms, but their specific meanings can become confusing without periodic review.
• Types of disinfectants - A sterilant* is an agent that can kill all microorganisms, including bacterial spores. A disinfectant is an agent that can kill most disease-producing microbes, but not bacterial spores. Bacterial spores are the hallmark microbe because of their very high resistance to killing by chemical and physical agents.
A high-level disinfectant is a chemical solution that can kill low levels of bacterial spores at the contact time recommended for disinfection on the product label (45-90 minutes for example). However, with an extended contact time (10 hours for example) the high-level disinfectant becomes a liquid sterilant able to kill high levels of bacterial spores.
These high-level killing agents act as a high-level disinfectant or a sterilant, depending on how they are used. Contact time is the time the item being treated is in direct contact with the killing agent.
High-level disinfectants/liquid sterilants are to be used as immersion products and not for surface disinfection. Examples are glutaraldehydes, special hydrogen peroxide, and special peracetic acid products. Items submerged should be limited to those that cannot be heat-sterilized (such as heat-sensitive plastic items).
An intermediate-level disinfectant is a chemical agent that does not kill bacterial spores but is tuberculocidal and kills other disease-producing microbes. Tuberculocidal indicates that the disinfectant has been shown capable of killing Mycobacterium tuberculosis var. bovis. This bacterium is very resistant to chemical killing and is a hallmark microbe for disinfectants much like bacterial spores are for sterilants.
Some examples of intermediate disinfectants include water-based phenolics, alcohol-based phenolics, iodophors, sodium hypochlorites and other chlorine compounds, and alcohol-based quaternary ammonium compounds. These disinfectants are used in dentistry as surface disinfectants.
The terms alcohol-based and water-based mean that either alcohol (ethanol or isopropanol) or water is also present with the main active ingredient. An alcohol-quaternary ammonium compound might contain ethanol and quaternary ammonium compounds (sometimes referred to as a "quat"), such as benzyl ammonium chloride or alkyldimethylethylbenzyl ammonium chloride.
- Low-level disinfectants - Low-level disinfectants are chemical agents that are not sporicidal or tuberculocidal, but can kill most other microorganisms. Low-level disinfectants are hospital-level disinfectants, which means that they have been shown capable of killing Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella choleraesuis. These three bacteria are not as resistant as Mycobacterium or bacterial spores, but they are more resistant than many other bacteria. Low-level disinfectants are not used to disinfect patient-care surfaces, but they are used on floors, walls, and some countertops. The most common type of low-level disinfectant is an alcohol-free quaternary ammonium compound.
- Virucidal activity - Most viruses are rapidly killed even with low-level disinfectants. However, some viruses are more resistant than others. This resistance is related to specific surface properties of the virus. Viruses that have an outer lipid (fat) layer on their surface (called an envelope) are referred to as lipophilic (fat-loving) viruses. This envelope is easily destroyed by a variety of chemicals, and its destruction inactivates the whole virus. So, lipophilic viruses - such as HIV, herpes simplex, and influenza - are easily killed by a wide variety of disinfectants, including low-level disinfectants.
Viruses that do not have a lipid envelope are called hydrophilic (water-loving) viruses. These viruses (such as polio virus, coxsackievirus) are more resistant to chemicals since they do not have the sensitive lipid layer on their outside.
Also, some intermediate viruses (such as adenoviruses, rotovirus) do not have an envelope; however, they are not quite as resistant as the hydrophilic viruses but are more resistant than the lipophilic viruses. They have an "intermediate" resistance.
- Use of disinfectants - A few terms relate to the use of disinfectants. One is contact time, defined above. Another is use-life, related to agents that must be activated (such as alkaline glutaraldehydes). Use-life is the length of time a product remains active after it has been activated. For alkaline glutaraldehydes, this time may be 14 days, 28 days, or 30 days (as specified on the product label). Precleaned surface or precleaning refers to cleaning an object or a surface before it is disinfected or sterilized. Thus, for proper surface disinfection, the surface is always precleaned and then disinfected. This also relates to the phrase spray-wipe-spray for surface disinfection. You "spray" on the disinfectant and "wipe" the surface (this is the precleaning step), and then you "spray" on the disinfectant and let it sit for the prescribed contact time.
The phrase kills the AIDS virus in one minute that appears on some disinfectant labels can be confusing. It suggests that the contact-time for using the disinfectant is only one minute. While this time may be sufficient to kill HIV, it would not be long enough to kill many other more resistant microbes.
In summary, disinfection is confusing simply because of the many products available and because of the differences in opinion about which types of disinfectants should be used. Hopefully, these descriptions of disinfection-related terms will aid understanding this important infection-control procedure.
* Some liquid sterilants cannot destroy prions such as the Creutzfeldt-Jakob disease agent.
Chris Miller, PhD, is professor of oral microbiology and executive associate dean at the Indiana University School of Dentistry.
