The ability of biological indicators to detect sterilization failures

The purpose of this study was to determine if a delay in analyzing biological indicators (BI's) after heat-processing prevents detection of sterilization failures. Sets of various types of BI's were processed through sublethal conditions in a steam, chemical vapor or dry heat sterilizer. Portions of each set of BI's were then analyzed for live spores immediately, after a 7-day delay at 27 degrees C, after a 7-day delay at 37 degrees C and in one instance after a 3-day mail delay. Of the 486 BI's exposed for sublethal times in steam at 250 degrees C, 483 (99.4%) exhibited spore growth (sterilization failure) after the 3-7 day delays before analysis. Of the 200 BI's exposed for sublethal times in the chemical vapor sterilizer, 193 (96.5%) exhibited spore growth after 7-day delays before analysis. All of the 120 (100%) BI's exposed for sublethal times in a static air dry heat sterilizer at 320 degrees F showed growth after 7-day delays before analysis. These results indicate that the delays before BI analysis described in this study do not cause any predictable pattern of preventing detection of sterilization failures.