Specifications for temperature and humidity in sterile storage environments - Where's the evidence?

The concept of event-related sterility for storage of medical devices is widely applied in Australian healthcare facilities. This paper reviews available literature, international standards and guidance documents with respect to the concept of event-related sterility in order to determine: (i) why commercially produced sterile medical devices may withstand adverse temperature and humidity conditions better than items produced in a Sterile Services Department; (ii) what effects temperature and humidity have on maintenance of sterility; and (iii) whether temperature and humidity conditions specified in AS/NZS4187:2003 are evidence-based and whether changes to these could be made in any future revisions. The literature review revealed that manufacturers of commercially available sterile medical devices are subject to stringent medical device regulations that require them to ensure that the devices remain both fit for purpose and sterile until use. This necessitates that manufacturers conduct accelerated ageing and environmental challenge tests to establish and justify the expiry dates given on the package label. The review also found a variety of specifications for temperature and humidity and the guidance documents gave no indication of evidence used as a basis for these requirements. In addition, it was apparent that many published studies on event-related sterility did not include consideration of the effect of temperature and humidity on the duration of sterility. After examination of a range of published material, it was concluded that the specifications in any future edition of AS/NZS4187 could be expanded to a temperature range of 16-25°C and a relative humidity range of 30-75%.