Proposed Use of a 50 % Limit of Detection Value in Defining Uncertainty Limits in the Validation of Presence-Absence Microbial Detection Methods

Validation of methods for microbial detection in foods or other matrices involves determining microbe recoveries. Recoveries are expressed qualitatively as presence-absence data, which are obtained from quantitative spiking experiments. Replicate samples of foods are spiked with the microbe of interest, generally at several concentration levels. Usually three different levels are used. However, only the data from the level which gives partial recovery are considered relevant. Such data are most reflective of a method’s detection endpoint but a limit of detection is rarely estimated. The calculation discussed here maximizes the use of the data from such trials by using data from more than one spiking level to calculate an LOD50.