A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 16-year-old man with no significant past medical, surgical, or family history presents to his pediatrician with new symptoms following a recent camping trip. He notes that he went with a group of friends and 1 other group member is experiencing similar symptoms. Over the past 5 days, he endorses significant flatulence, nausea, and greasy, foul-smelling diarrhea. He denies tenesmus, urgency, and bloody diarrhea. The blood pressure is 118/74 mm Hg, heart rate is 88/min, respiratory rate is 14/min, and temperature is 37.0°C (98.6°F). Physical examination is notable for mild, diffuse abdominal tenderness. He has no blood in the rectal vault. What is the patient most likely to report about his camping activities?
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A
Collecting water from a stream, without boiling or chemical treatmentCorrect. Drinking untreated stream water during camping is the classic exposure for Giardia, which causes precisely this picture of foul greasy diarrhea and flatulence without blood or fever.
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B
This has been going on for months.Incorrect. Months of chronic symptoms would suggest other diagnoses like IBS, microscopic colitis, or chronic giardiasis (which can occur but is less classic).
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C
The patient camped as a side excursion from a cruise ship.Incorrect. Cruise ship outbreaks suggest Norovirus (acute watery diarrhea with vomiting) rather than the steatorrhea pattern here.
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D
The patient camped in Mexico.Incorrect. Mexico camping suggests enterotoxigenic E. coli (traveler's diarrhea, acute watery), or Shigella, or amebiasis — but the classic stream-water exposure and steatorrhea here points to Giardia.
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E
The patient ate undercooked ground beef at a cookout.Incorrect. Undercooked ground beef suggests enterohemorrhagic E. coli (O157:H7) causing bloody diarrhea and HUS — not the non-bloody, foul, greasy steatorrhea characteristic of Giardia.
↑ Tap an answer to reveal the reasoning
Answer: A. A teenager develops flatulence, nausea, and greasy, foul-smelling diarrhea (steatorrhea) 5 days after a camping trip — the classic presentation of giardiasis, caused by Giardia lamblia (G. intestinalis), the most common protozoal cause of diarrhea in the US.
Giardia is transmitted by the fecal-oral route, most often through ingestion of CONTAMINATED STREAM OR LAKE WATER (cysts survive cold water and are resistant to standard chlorination). Backpackers, campers, hikers, and travelers who drink untreated surface water are the prototypical patients. After ingestion, Giardia trophozoites attach to the duodenal/jejunal mucosa, impairing nutrient and fat absorption — hence the malodorous fatty diarrhea, flatulence (a remarkably specific symptom), and cramping. Importantly, there is no blood, mucus, or fever, distinguishing Giardia from invasive bacterial pathogens like Shigella, Salmonella, or EHEC.
Diagnosis: stool antigen ELISA or PCR (more sensitive than ova-and-parasite microscopy, which shows the classic trophozoite with two nuclei resembling "owl eyes"). Treatment is oral metronidazole or tinidazole. Prevention: boil, filter, or chemically treat (iodine, chlorine dioxide) surface water before drinking.
**Why each option:**
**A.** Correct. Drinking untreated stream water during camping is the classic exposure for Giardia, which causes precisely this picture of foul greasy diarrhea and flatulence without blood or fever.
**B.** Months of chronic symptoms would suggest other diagnoses like IBS, microscopic colitis, or chronic giardiasis (which can occur but is less classic).
**C.** Cruise ship outbreaks suggest Norovirus (acute watery diarrhea with vomiting) rather than the steatorrhea pattern here.
**D.** Mexico camping suggests enterotoxigenic E. coli (traveler's diarrhea, acute watery), or Shigella, or amebiasis — but the classic stream-water exposure and steatorrhea here points to Giardia.