Are multiple stool samples needed for protozoa?

Some studies, such as McHardy et al (2014) found that

The diagnostic yield of the O&P is also significantly impacted by the number of stool specimens collected and submitted to the laboratory for testing. Many intestinal protozoa are irregularly shed, and data suggest that a single stool specimen submitted for microscopic examination will detect 58 to 72% of protozoa present. Hiatt and colleagues found that evaluating three specimens, as opposed to one, resulted in an increased yield of 22.7% for E. histolytica, 11.3% for Giardia, and 31.1% for D. fragilis. As such, many laboratories continue to request 3 specimens be collected and submitted for testing; specimen collection is made, optimally, every other day, over a period of up to 10 days.

However, the same study also noted that alternative approaches have been proposed to help curtail unnecessary testing.

Enhanced sensitivity of molecular detection methods may require only 1 specimen for testing to achieve sensitivity equal to, if not greater than, microscopy. One study demonstrated a 14% increase in yield for gastrointestinal protozoa when a real-time PCR (for which Vibrant uses) was performed on a single stool specimen, compared to microscopy on three specimens.


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