Does a negative stool examination for ova and parasites rule out an intestinal parasitic infection?
A single negative stool examination does not exclude a parasitic infection, since the sample may have been collected during the prepatent period (i.e., the time between infection and the production of detectable ova or larvae) or because the target organism may have been shed inconsistently or in low numbers, as is frequently the case with strongyloides larvae.
New England Journal of Medicine - Vol. 359, No. 1, July 3, 2008