The foundation of environmental decontamination is identification, removal and treatment (if a shelter has the appropriate housing/space and resources) of affected animals coupled with careful mechanical cleaning. Disinfection is an important part of the protocol but is adjunct to mechanical removal.
Clean all surfaces three times with any good detergent and clean rags. Follow this mechanical removal with a disinfectant. Concentrated bleach or even diluted at 1:10 is too harsh to be routinely used and thankfully is not necessary. Effective disinfectants include Accel/Rescue® (Accelerated hydrogen peroxide 1:16), Accel® TB (hydrogen peroxide 0.5%.), Enilconazole, bleach diluted 1:32 with prolonged contact time (at least 10 minutes), 2% Potassium Peroxymonosulfate, Formula 409® (quaternary ammonium 0.3%), and Clorox Clean-Up® (sodium hypochlorite 1.84%,). These have all been shown to be very effective on pre-cleaned surfaces where all organic matter has been removed. For additional specific information regarding the efficacy of various cleaning compounds against ringworm spores, see this 2013 study in Veterinary Dermatology.
High heat (> 110oF) is also effective. This temperature can be attained by commercial dishwashers, some commercial steam applicators (but not necessarily home steam carpet cleaners) and clothes dryers.
Environmental decontamination is usually straightforward in a typical shelter with easily disinfected and mechanically cleaned cages. It can present a much greater problem in a home or more home-like environment such as a group cat room.
Application of harsh disinfectants to every contaminated surface is an impossible goal in such environments. Fortunately, much can be accomplished through identification, removal and treatment of carrier animals, followed by repeated application of elbow grease.
Fungal cultures from the environment can take the guesswork out of decontamination, and spare a lot of unnecessary work and worry. First clean carefully and disinfect where possible, then take cultures of possibly contaminated areas to evaluate success (see below for Swiffer swab method.) If the culture is negative, the area can probably be safely re-opened to feline inhabitants. If positive, at least you know for sure you have to go back and try again. This can save a lot of agony over whether to replace carpets, furniture etc. The five D’s of ringworm decontamination are:
Repeat the five D’s as necessary until environmental cultures are negative!