Comparative thermoresistance of two biological indicators for monitoring steam autoclaves. 2. Comparison performed at 134 degrees C in a hospital prevacuum steam sterilizer.

The thermoresistance of various lots of two biological indicators (BIs) for steam sterilization control, a Scandinavian BI (SBI) and the Attest BI (ABI), were compared during sterilization cycles in a hospital prevacuum (pressure-pulsing) steam autoclave at 134 degrees C, saturated steam. ABI No. 1242, ABI No. 1262 (its replacement) and incremental heat exposure times between 0 s and 180 s were used. The intrachamber temperature and pressure were continuously measured and monitored throughout the sterilization cycles. The results showed that both of the ABIs were more thermoresistant than the SBI, giving 33.1% (ABI No. 1242), 18.9% (ABI No. 1262), and 0% (SBI) autoclave survivors. Because the time needed to reach 134 degrees C (preconditioning time) increased as the day progressed, and varied from day to day, correlation between individual incremental heat exposure times and the number of surviving BI units was not possible. Standardized test conditions are necessary for a true comparison of BIs.