Disinfection prevents infection by reducing the number of potentially infective organisms by killing, removing, or diluting them. Disinfection can be accomplished by application of chemical agents or use of physical agents such as ionizing radiation, dry or moist heat, or superheated steam (autoclave, 120°C) to kill microorganisms. Often a combination of agents is used, eg, water and moderate heat over time (pasteurization); ethylene oxide and moist heat (a sterilant); or addition of disinfectant to a detergent. Prevention of infection also can be achieved by washing, which dilutes the potentially infectious organism.
Hand hygiene is probably the most important means of preventing transmission of infectious agents from person to person or from regions of high microbial load, eg, mouth, nose, or gut, to potential sites of infection. Alcohol-based hand rubs and soap and warm water are used to remove bacteria. Skin disinfectants along with detergent and water are usually used preoperatively as a surgical scrub for surgeons’ hands.
Evaluation of effectiveness of antiseptics, disinfectants, and sterilants, although seemingly simple in principle, is very complex. Factors in any evaluation include the intrinsic resistance of the microorganism, the number of microorganisms present, mixed populations of organisms, amount of organic material present (eg, blood, feces, tissue), concentration and stability of disinfectant or sterilant, time and temperature of exposure, pH, and hydration and binding of the agent to surfaces. Specific, standardized assays of activity are defined for each use. Toxicity for humans also must be evaluated. In the USA, the Environmental Protection Agency (EPA) regulates disinfectants and sterilants and the FDA regulates antiseptics.
Users of antiseptics, disinfectants, and sterilants need to consider their short-term and long-term toxicity because they may have general biocidal activity and may accumulate in the
TABLE 50–1 Activities of disinfectants.
Bacteria Viruses Other Gram-Positive Gram-Negative Acid-Fast Spores Lipophilic Hydrophilic Fungi Amebic Cysts Prions Alcohols (isopropanol, HS HS S R S V — — R conc, concentration; HS, highly susceptible; MS, moderately susceptible; —, no data; R, resistant; S, susceptible; V, variable.
environment or in the body. Disinfectants and antiseptics may also become contaminated by resistant microorganisms—eg, spores, P aeruginosa, or Serratia marcescens—and actually transmit infection. Most topical antiseptics interfere with wound healing to some degree. Cleansing of wounds with soap and water may be less damaging than the application of antiseptics.
Some of the chemical classes of antiseptics, disinfectants, and sterilants are described briefly in the text that follows. The reader is referred to the general references for descriptions of physical disinfection and sterilization methods.
The two alcohols most frequently used for antisepsis and disinfection are ethanol and isopropyl alcohol (isopropanol). They are rapidly active, killing vegetative bacteria, Mycobacterium
TABLE 50–2 Commonly used terms related to chemical and physical killing of microorganisms.
Antisepsis Application of an agent to living tissue for the purpose of preventing infection
Decontamination Process that produces marked reduction in number or activity of microorganisms
Disinfection Chemical or physical treatment that destroys most vegetative microbes and viruses, but not spores, in or on inanimate surfaces
Sanitization Reduction of microbial load on an inanimate surface to a level considered acceptable for public health purposes