Review Question - QID 108889

This patient is presenting with flatulence, bloating, and foul-smelling diarrhea suggestive of giardiasis. The first-line treatment for giardiasis is metronidazole.

The clinical presentation of flatulence, bloating, and foul-smelling diarrhea following a hiking trip is characteristic of giardiasis. The stool sample demonstrating a flagellated trophozoite confirms the diagnosis of giardiasis. Giardia lamblia is an anaerobic protozoon that is usually transmitted to humans via waterborne cysts that are ingested by drinking water from mountain streams. They can be seen on histology as flagellated trophozoites that “look back at you.” The first-line therapy for symptomatic giardiasis is metronidazole, an antibiotic and anti-protozoal agent. Of note, patients with IgA deficiency are at an increased risk of developing giardiasis due to an inability to mount an immune response against mucosal parasitic infections. Giardia rarely causes bloody diarrhea, so the blood on the toilet paper in this case likely stemmed from abrasion due to excessive wiping.

Figure A demonstrates the classic appearance of giardia lamblia. Note the flagellated trophozoite that has a “smiley face.”

Incorrect Answers:
Answer 2: Ciprofloxacin is a fluoroquinolone antibiotic. It is not used in the treatment of giardiasis but does have an indication for severe infectious diarrhea.

Answer 3: Ampicillin is a cell-wall synthesis inhibitor that is used to treat gram-positive and some gram-negative infections. It is not used in the treatment of giardiasis but it is the first-line treatment for diarrhea due to Listeria monocytogenes.

Answer 4: Vancomycin is a cell-wall synthesis inhibitor that is used to treat gram-positive infections. It is not used in the treatment of giardiasis but it is the first-line treatment for diarrhea due to Clostridium difficile colitis. This would present as abdominal pain and watery stools after a course of antibiotics.

Answer 5: Sulfasalazine is a sulfa-based anti-inflammatory medication that is used to treat Crohn's disease and ulcerative colitis. It is also used to treat rheumatoid arthritis. Inflammatory bowel disease would present with weight loss, bloody stools (not just blood on toilet paper) and abdominal pain.

Bullet Summary:
Giardiasis is a protozoal infection that causes fatty foul-smelling diarrhea by attaching to the lining of the duodenal wall and leading to malabsorption. The first-line treatment for giardiasis is metronidazole.