A 29-year-old man comes to the office due to 10 days of fatigue and copious watery diarrhea. He has had no fever, stool with blood or mucus, tenesmus, or vomiting. The patient returned a week ago from a 3-week trip to Eastern Europe. During this trip, he spent much time hiking and swimming in local lakes and streams. He has no chronic medical problems and takes no medications. The patient does not use tobacco, alcohol, or illicit drugs. Temperature is 37.2 C (99 F), blood pressure is 120/74 mm Hg, pulse is 80/min, and respirations are 15/min. Cardiopulmonary auscultation is normal. The abdomen is soft and nontender with increased bowel sounds and no organomegaly. Stool is negative for leukocytes and fecal occult blood. Which of the following pathogens is most likely responsible for this patient's symptoms?
Although bacterial and viral pathogens are the most common causes of travelers' diarrhea, parasitic organisms such as Cryptosporidium parvum, Cyclospora, and Giardia are responsible for most cases of prolonged, profuse, watery diarrhea.
C parvum is an intracellular protozoan transmitted via the ingestion of contaminated water (drinking, swimming). Oocytes release sporozoites that penetrate intestinal epithelial cells, resulting in altered villous architecture. Although a minority of patients remain asymptomatic, most develop mild or profuse watery diarrhea. Malaise, nausea, crampy abdominal pain, and low-grade fever may also occur.
Fecal laboratory testing is rarely positive for leukocytes or blood, but microscopy with specialized stains is usually diagnostic (routine stool ova and parasite testing does not identify C parvum). Otherwise healthy adults typically have spontaneous resolution of symptoms within 10-14 days; however, patients who are immunocompromised (eg, AIDS) are at risk for severe, chronic disease.
(Choice A) Most cases of Clostridioides difficile arise in those who have recently been hospitalized or treated with antibiotics, or those on antacids. Manifestations include watery diarrhea (often with mucus or occult blood), abdominal pain, cramping, and leukocytosis. This patient has no risk factors for C difficile infection, and the pathogen is not a common cause of travelers' diarrhea.
(Choice C) Entamoeba histolytica is a rare cause of travelers' diarrhea (eg, <0.5% in a study from Germany); it typically presents subacutely in individuals who live or have spent extended time (eg, months) in an endemic area.
(Choice D) Shigella flexneri can cause travelers' diarrhea but is typically associated with dysentery (bloody, mucoid diarrhea).
(Choice E) Strongyloides stercoralis is a helminth that typically causes mild, intermittent skin, gastrointestinal, and pulmonary symptoms over the course of years. Although diarrhea and abdominal pain may occur, profuse watery diarrhea would be atypical.
Educational objective:
Travelers' diarrhea that is prolonged, profuse, and watery is often due to a parasitic pathogen such as Cryptosporidium parvum. C parvum infections may be transiently severe but are typically self-limited in otherwise healthy individuals (resolving spontaneously in 10-14 days). Patients who are immunocompromised (eg, AIDS) are at risk for chronic infection.