Abdominal examination may reveal nonspecific tenderness without evidence of peritoneal irritation. Rectal examination should reveal heme-negative stools. In severe cases, evidence of dehydration or wasting may be present. Giardiasis is caused by the ingestion of infective cysts. Giardia was implicated in 90 waterborne outbreaks in the US from 1964-1984, affecting 23,500 persons.
Venereal transmission occurs through direct fecal-oral transmission.
At least 3 stools taken at 2-day intervals should be examined for ova and parasites. Trophozoites may be found in fresh, watery stools but disintegrate rapidly. If the stool is not fresh or is semiformed to formed, trophozoites will not be found. Cysts are passed in soft and formed stools. If not immediately examined, stool should be preserved in polyvinyl, alcohol, or a formalin preparation.