Gerald E. McDonnell - Antisepsis, Disinfection, and Sterilization

TABLE 1.22 Examples of biological-indicator standards

a ISO, International Standards Organization; EN, European Norm, from the CEN (European Committee for Standardization); USP, United States Pharmacopeia; EP, European Pharmacopoeia.

Other, miscellaneous indicators include mechanical indicators, such as gauges or sensors that measure temperature, concentration, pressure, time, etc., that are used to monitor various physical parameters during a given process and cleaning indicators that use artificial test soils inoculated onto a surface to test (generally by visual inspection) physical removal during a cleaning process or cycle. Mechanical indicators play an important role in the parametric release of a product or process as an alternative to the use of chemical and biological indicators for routine monitoring of sterilization processes (see section 1.4.2.4).

TABLE 1.23 A typical classification of chemical indicators

FIGURE 1.24 Example of a chemical-indicator color change.

The concept of parametric control (or release) as a method to verify the effectiveness of a biocidal process is based on the understanding of all the key physical parameters that can affect its success or failure. Although theoretically this could be applied to any disinfection or sterilization process, it is generally restricted to well-characterized sterilization methods, including steam, dry heat, ethylene oxide, and ionizing radiation. An example is steam sterilization. The efficacy of steam is affected by the temperature and time, but also by the presence of air (see section 5.2). These parameters are reasonably well understood and can be physically measured (by using mechanical indicators [see section 1.4.2.3]) to ensure that the correct conditions have been met during a given steam sterilization cycle. In addition to monitoring these conditions, a series of in-process tests and controls are also conducted to provide further assurance that the sterilization process has been efficient. However, the concern with parametric release as an alternative to biological monitoring is in the control of other variables that can affect the effectiveness of the process. In the case of steam, these include the quality of the steam (see section 5.2), variations in the load being sterilized, and in the case of reusable devices, if the cleaning process has been sufficient prior to sterilization (see section 1.4.8). In most cases, disinfection and sterilization processes are routinely tested and monitored using a combination of biological and chemical indicators in parallel with mechanical indicators for parametric control.

TABLE 1.24 Examples of chemical-indicator standards

a ISO, International Standards Organization; EN, European Norm, from the CEN (European Committee for Standardization); ANSI/AAMI, American National Standards Institute/Association for the Advancement of Medical Instrumentation.