Heat has the widest range of efficacy among all disinfection methods, without the risk of user toxicity. Certain pathogens are difficult to kill: parvovirus, protozoal oocysts, mycobacteria, bacterial spores, and prions resist most disinfectants but can be eliminated by the application of heat, especially steam, which will kill protozoal oocysts.
Moist heat is more effective than dry heat, especially under pressure. The most efficient sterilization method, for example, is the use of pressurized steam (ie, autoclaving). The recommended autoclave settings for sterilization are 121°C at 15 psi for 15 minutes, or 126°C at 20 psi for 10 minutes. To inactivate prions requires a temperature of 130°C for 30–60 minutes. When autoclaves are not available, surgical instruments that have already been scrubbed can be boiled for some measure of sterility. Commonly available steam cleaners can be used to sterilize soft furnishings (such as carpet), floors, and work surfaces.
In veterinary hospitals, shelters, and the home, infective agents can be inactivated with heat provided by common appliances such as dishwashers, washing machines, and steam cleaners, as well as by incinerators. Dishwashers and washing machines must be used properly so they do not become a source of cross-contamination themselves: Cryptosporidium, Microsporum, and parvovirus are all noteworthy examples of pathogens that can be spread between items by inadequate laundering practices. Sterilization efficacy depends on the duration of exposure of the pathogen to heat, and on whether a chemical disinfectant is also used. Specifically, t
Temperatures in washing machines and dishwashers should be at least 60°C to eliminate pathogenic spores and inactivate resistant viruses such as feline calicivirus (FCV). Standard washing machines may not achieve these critical temperatures; use of a steam cycle may be required. Furthermore, parvovirus can resist temperatures of 80°C for at least 1 hour; the addition of chemical disinfectant (bleach) is essential for elimination of this organism. For fungal pathogens, reliable decontamination can be achieved by laundering at 60°C, regardless of the textiles and detergents used. Temperatures of ≥56°C will kill 99% of Giardia cysts. The temperature needed for decontamination depends on washing time and detergent type. Two additions have been shown to improve the sterilization effectiveness of washing machines in laundry: sodium hypochlorite with detergent substantially decreases the number of virus particles present, and activated oxygen bleach improves effectiveness against a number of bacteria.
