Trace, refrigeration doesn't always kill coccidia but the oocyst's hard coating becomes more rigid and resistant to stains and dyes, and therefore harder to pick up in a slide. Samples less than 2 hours old that have never been refrigerated are the most accurate.
If you must refrigerate a sample, place a wet paper towel in the plastic bag to keep it from dehydrating as quickly. That will help bacteria and protozoa from going into their stasis state when confronted with cold dry conditions.
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