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Published online by Cambridge University Press: 21 June 2016
Extract
The performance of a biological indicator (BI) over a range of sterilization temperatures is known as a z value and, as defined by Roberts, is “the number of degrees change in temperature to achieve a tenfold change in the D value.” A plot of the D values versus exposure temperatures will reveal the z value as the negative reciprocal of the slope of the resulting thermal resistance curve. Historically, paper strip carriers of Bacillus stearothermophilus spores have been found to possess a z value in the range of l7°-2O°F, whereas self-contained BIs tested in our laboratories have exhibited z values as high as 64°F (Figure I), which reflects their excessively high resistance at flash sterilization temperatures. In general, such matters are not of concern to the end user until such time as false positives are encountered during flash sterilization.
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- Copyright © The Society for Healthcare Epidemiology of America 1988
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