Table 1 Factors Affecting Efficacy of Disinfection



Concentration of disinfectant Each disinfectant has a minimum concentration for potency  against particular pathogens in suspension; when contaminants are dried onto a surface, the concentration required is invariably higher
Formulation of disinfectant Even if 2 products have the same nominal concentrations of  active ingredients, other components of the formulations may affect relative efficacy
Target organism(s)* Pathogens have different degrees of resistance to germicides;  although there is definite overlap between classes depending on organism and product, the order of resistance is generally considered to be as follows: bacterial spores > non enveloped viruses = mycobacteria > fungi > enveloped viruses = vegetative bacteria
Contact time Disinfectants should be applied for at least the time specified on the product label as this has been validated by the manufacturer
Temperature Efficacy of disinfection generally increases with temperature; therefore, it is important to observe the minimum temperatures given on label instructions
Water hardness Hard water can diminish product efficacy; consult product label or the manufacturer
Soil load Inorganic or organic soil remaining on surfaces can partially neutralize applied disinfectants by interaction and can help to shield microbial contaminants from contact with the disinfectant
Biofilm presence Surfaces that are continuously or frequently wet or damp develop microbial biofilms, which can be very resistant to disinfection
Surface microtopography Even apparently flat surfaces have many scopic irregularities,  which can shield microorganisms from proper contact with the disinfectant; formulations often contain wetting agents to facilitate such contact
Precleaning The compatibility of precleaners and disinfectants must be verified, especially for quaternary ammonium compounds
pH Disinfectants are usually designed to work optimally at a specified pH
Relative humidity Relative humidity of the room affects penetration of the disinfectant into dried material
Compatibility Some surfaces are incompatible with certain types of disinfectants
Application method The amount of disinfectant delivered to the target depends on  whether it is applied by immersion, flooding, brushing or wiping; moreover, the nature of the applicator should be compatible with the type of disinfectant and the applicator must be clean, so as not to neutralize the applied disinfectant
Application rate The ratio between the target contamination and the applied disinfectant is important, especially when soiling is present: the amount to be applied per unit area is not usually specified by the manufacturer
Storage Disinfectant should always be stored according to the manufacturer’s directions
Product age Disinfectant should always be used within the manufacturer’s specified shelf life

*In practice, the contaminating microorganisms are not usually known.