Hydrogen peroxide is a very effective disinfectant when used for inanimate objects or materials with low organic content such as water. Systems that produce hydrogen peroxide vapor or dry mist are now available for room decontamination in healthcare facilities. Organisms that produce the enzymes catalase and peroxidase rapidly degrade hydrogen peroxide. The innocuous degradation products are oxygen and water. Concentrated solutions containing 90% weight per volume H2O2 are prepared electrochemically. When diluted in high-quality deionized water to 6% and 3% and put into clean containers, the products remain stable. Concentrations of 10–25% hydrogen peroxide are sporicidal. Vapor phase hydrogen peroxide (VPHP) is a cold gaseous sterilant that has the potential to replace the toxic or carcinogenic gases ethylene oxide and formaldehyde. VPHP does not require a pressurized chamber and is active at temperatures as low as 4°C and concentrations as low as 4 mg/L. It is incompatible with liquids and cellulose products. It penetrates the surface of some plastics. Automated equipment using vaporized hydrogen peroxide or hydrogen peroxide mixed with formic acid is available for sterilizing endoscopes.
Peracetic acid (CH3COOOH) is prepared commercially from hydrogen peroxide, acetic acid, and a catalyst such as sulfuric acid. It is explosive in the pure form. It is usually used in dilute solution and transported in containers with vented caps to prevent increased pressure as oxygen is released. Peracetic acid is more active than hydrogen peroxide as a bactericidal and sporicidal agent. Concentrations of 250–500 ppm are effective against a broad range of bacteria in 5 minutes at pH 7.0 at 20°C. Bacterial spores are inactivated by 500–30,000 ppm peracetic acid. Only slightly increased concentrations are necessary in the presence of organic matter. Viruses require variable exposures. Enteroviruses require 2000 ppm for 15–30 minutes for inactivation.
An automated machine that uses buffered peracetic acid liquid of 0.1–0.5% concentration has been developed for sterilization of medical, surgical, and dental instruments. Peracetic acid sterilization systems have also been adopted for hemodialyzers. The food processing and beverage industries use peracetic acid extensively because the breakdown products in high dilution do not produce objectionable odor, taste, or toxicity, and rinsing is not necessary.
Peracetic acid is a potent tumor promoter but a weak carcinogen. It is not mutagenic in the Ames test.
Ultraviolet irradiation is used in some health care facilities as an alternate mode of disinfection for patient care areas. It is typically employed via an automated system, allowing for less staff exposure to decontamination products. It has rapid cidal activity against numerous pathogens, providing effective decontamination for most vegetative bacteria in less than 25 minutes and against C. difficile in less than one hour.
Heavy metals, principally mercury and silver, are now rarely used as disinfectants. Mercury is an environmental hazard, and some pathogenic bacteria have developed plasmid-mediated resistance to mercurials. Hypersensitivity to thimerosal is common, possibly in up to 40% of the population. These compounds are absorbed from solution by rubber and plastic closures. Thimerosal 0.001– 0.004% is still used safely as a preservative of vaccines, antitoxins, and immune sera. Although a causative link to autism has never been established and the original claim was found to be fraudulent, thimerosal-free vaccines are available for use in children and pregnant women.