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Sample Size Determination for Microbial Challenge Testing

We are currently looking for Container Closure Integrity Testing using the Microbial Immersion/Challenge Test.
I am unable to determine the sample size for the test that would represent the whole batch or give us an assurance that the container/closure system will be integral and sterile post-capping.

I was asked to determine the sample size using statistical approach. I looked online for determining sample size based on confidence level and confidence interval but I am getting confused if I am approaching the right way.

Any help would be greatly appreciated.


Hello there,

The CCIT by microbial immersion would produce Pass/Fail results. Considering the high risk in failure, your acceptance rate would be much lower (close to zero). It is generally acceptable by the Agency that a 95% confidence in sufficient for Sterile Products. You need to justify that whatever samples you are selecting (considering “zero” rejects) you are 95% confident that your accept/reject rate falls in the confidence interval. Here is a very good article explaining the sample size and confidence interval relation -