Giardiasis: An Under-Diagnosed Cause of Common Gastrointestinal Symptoms

Abstract

Purpose: 1) To discuss giardiasis as an important but sometimes under-diagnosed etiology of common gastrointestinal symptoms. 2) To highlight the importance of basic diagnostic principles. Case: A 27-year-old male was referred to our center for a second opinion on chronic diarrhea. He complained of a 5-year history of 8 to 10 non-bloody, watery bowel movements, sometimes nocturnal. He also had intermittent, lower crampy abdominal pain. There was no fever, vomiting or weight loss. The patient sometimes consumed well water. Multiple upper endoscopic, colonoscopic and abdominal computed tomographic examinations had previously been negative. Duodenal, terminal ileal and colon biopsies had been read as normal. He was eventually diagnosed with irritable bowel syndrome and was treated with fiber, loperamide, antispasmodic agents and cholestyramine with no relief. Initial work-up in our clinic included blood tests to rule out anemia, hypoalbuminemia, hyperthyroidism and to screen for celiac disease. These were negative. Stool microscopy for ova, cysts and parasites was positive for Giardia lamblia cysts and trophozoites. Stool Giardia antigen was also positive. Review of outside duodenal biopsies from 2 years earlier showed Giardia organisms. No further diagnostic testing was recommended. The patient's symptoms partially responded to a 5-day course of metronidazole. He subsequently had a complete response to treatment with single-dose tinidazole. Discussion:Giardia lamblia is the most common gastrointestinal parasite in the United States. Well water is often implicated in the waterborne transmission of the pathogen. Symptoms can be variable and non-specific but diarrhea is the most frequently reported symptom. Stool microscopy of a single specimen can detect the organism in 50 percent of cases; the detection rate increases with three specimens. Stool antigen testing has a sensitivity and specificity of approximately 90 and 100 percent respectively. Duodenal biopsies can reveal the diagnosis but are usually normal. Oral metronidazole is commonly used as first-line treatment. Single-dose tinidazole is highly effective and Food and Drug Administration (FDA)-approved for the treatment of giardiasis. Conclusions: Giardiasis is the most common gastrointestinal parasitic infection in the United States and an important etiology of gastrointestinal symptoms in adults. It can easily be diagnosed by non-invasive stool tests. This case highlights the importance of awareness and maintaining a high index of suspicion for the disease, particularly in patients with risk factors. This case also demonstrates that a thorough diagnostic work-up does not necessarily translate to invasive, repetitive or costly testing.