Numbers of Giardia in the feces of infected children.

Estimates were made of the number of Giardia in 1,090 stools from 15 infected children over periods of 1 to 3 months. Three patterns of excretion were observed: 1) high, with the parasite abundant in nearly all stools; 2) low, with the parasite detectable in only 40% of the stools and scanty when present; and 3) mixed, with periods of 1 to 3 weeks of high excretion alternating with generally shorter periods of low excretion, and an overall average of about 60% of stools positive. The presence and relative numbers of Giardia in the feces apparently were unrelated to either the consistency of the stools or frequency of defecation. Attempts to increase parasite excretion with purgatives were, on the whole, unsuccessful.