Comparison of a rapid readout biological indicator for steam sterilization with four conventional biological indicators and five chemical indicators.

OBJECTIVE

In this study, we compare a new biological indicator that provides results within 3 hours with four conventional, 48-hour biological indicators and five chemical indicators.

DESIGN

Biological indicators tested included the conventional Attest 1262, Proof Plus, Assert, and Biosign, and the new Attest 1292 Rapid Readout biological indicator. Chemical indicators tested included Comply, Propper, Chemdi, Sterigage, and Thermalog S. Spore survival following 121 degrees C in a gravity displacement sterilizer was measured by media color change after incubation for 24 and 48 hours at 56 degrees C for the conventional biological indicators, fluorescence at 3 hours for the Attest 1292 Rapid Readout biological indicator, and color change for the chemical indicators. Each exposure time was replicated 12 times with 5 samples of each indicator per run (ie, 60 replicates per indicator).

RESULTS

At 48 hours, the conventional biological indicators Attest 1262, Proof Plus, Assert, and Biosign showed 100%, 95%, 88%, and 93% spore survival at 5 minutes' exposure 0%, 0%, 0% and 8% at 10 minutes; and all showed 0% survival at 15 minutes' exposure. Following a 3-hour incubation, the Attest 1292 Rapid Readout biological indicator showed fluorescence at 100%, 72%, and 0% at 5, 10, and 15 minutes, respectively. The chemical indicators Comply, Propper, Chemdi, Sterigage, and Thermalog S revealed sterilization failure rates of 100%, 100%, 100%, 100%, and 100% at 5 minutes' exposure; 0%, 0%, 0%, 92%, and 100% at 10 minutes; and 0%, 0%, 0%, 3%, and 27% at 15 minutes' exposure, respectively.

CONCLUSIONS

The sensitivity of the Attest 1292 Rapid Readout biological indicator parallels that of conventional biological indicators. These data suggest that a 3-hour rapid readout biological indicator is equivalent to a standard 48-hour biological indicator. Some chemical indicators (eg, Thermalog S) failed to indicate adequate sterilization at 15 minutes' exposure. These chemical indicators have the potential of causing unnecessary recall of adequately sterilized items.