The incubation period in sterility testing.

Sterility test results gathered over a ten year period have been analysed to determine the effects of the incubation period. Overall there was no difference between the membrane filtration test and direct inoculation in the time required for visible growth of contaminants. Growth occurred earlier if products had no preservative or antimicrobial substances. However use of the membrane filtration method did not significantly enhance the efficiency of detection at seven days incubation. Regardless of the nature of the product or the method of test an unacceptable proportion of contaminants would be missed by limiting incubation to seven days.