Diarrhea lasting several weeks usually without fever; [PPID, p. 3157]
Many infections are asymptomatic. Acute symptoms include malodorous diarrhea, cramping, and nausea. Chronic symptoms include diarrhea, distention, flatus, and weight loss. [Merck Manual, p. 1371-2] About 1/4 of patients have vomiting and <20% have fever. Other findings occasionally described are urticaria and reactive arthritis. Patients may be lactose intolerant for several weeks after completion of treatment. Eosinophilia is not seen. [Guerrant, p. 623-30] Fever and blood in stool suggest another diagnosis. Patients with chronic infection may have episodes rather than continual symptoms. In some cases, diarrhea is less prominent than belching, flatulence, and weight loss. [Harrison ID, p. 1208-9] Giardiasis is associated with arthritis, uveitis, and urticaria, but it is not yet known if it causes these conditions. Giardiasis is an uncommon cause of cholecystitis and pancreatitis. [Cecil, p. 2042] Initial stool specimens may be negative because the incubation period can be shorter than the prepatent period (time necessary for cysts to be formed in the stool). Some patients have episodes of diarrhea along with normal bowel movements and constipation. [PPID, p. 3157]
Humans, cats, dogs, cattle, beaver and other animals may carry the infection. Children may become infected in daycare centers. Infection is also acquired by drinking or swimming in contaminated water or eating contaminated food. [CCDM, p. 235] Backpackers who drink untreated surface water are at risk. Certain sexual practices (fecal-oral contact) increase risk. [Cecil, p. 2041] Other mammals that may be infected are dogs, cats, sheep, cattle, beavers, gerbils, and mice. [PPID, p. 3528] As few as 10 cysts can cause infection. Cysts can remain viable for months in cold water and are not destroyed by standard techniques of water chlorination. Leaking sewer lines may contaminate outmoded water systems. [Harrison ID, p. 1207]
For updated text and symptoms of infectious diseases, see iddx.com.
Stool antigen detection with immunofluorescence (DFA) most sensitive/specific;. PCR available. [ABX Guide] Direct immunofluorescent microscopy is 90% sensitive on a single stool sample. [Cecil, p. 2042]