Factor |
Comments |
| 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.