The need for three stool specimens in routine laboratory examinations for intestinal parasites.

This study was designed to test whether three sequential stool specimens are necessary for reliable detection of intestinal parasites in routine laboratory examinations. There were 175 patients in whom a single species of intestinal parasite or ova was identified on at least one occasion when three stool specimens were examined over a period of 14 days from the first recorded specimen. Examination of a first stool specimen detected parasites and/or ova in 102/175 patients (58.3%); examination of a second specimen identified an additional 36 positive patients (20.6%) and examination of a third specimen yielded a final 37 previously undetected patients (21.1%). These findings indicate that at least three stool specimens should be examined to confirm the presence of intestinal parasites. Even with such practice, it is not possible to guarantee that there is no infestation, but examination of fewer specimens would run a definite risk of false negative results.