A 55-year-old woman presents to a primary care physician with persistent nausea and abdominal discomfort. She has experienced these symptoms daily for the past 3 months. She feels bloated and has episodic loose and watery stools. She has a history of hypertension and hyperlipidemia for which she takes amlodipine and atorvastatin. She immigrated from Vietnam 6 months ago. Her temperature is 98.6°F (37.0°C), blood pressure is 110/60 mmHg, pulse is 70/min, and respirations are 18/min. Physical exam reveals a thin-appearing woman in no acute distress. Her mucous membranes are moist. Cardiac and lung examinations are unremarkable. Laboratory results are as follows: Leukocyte count: 13,000/mm^3 Segmented neutrophils: 54% Bands: 2% Eosinophils: 6% Basophils: 0.4% Lymphocytes: 30% Monocytes: 5% A vitamin D level is 26 ng/mL (reference: >= 30 ng/mL). Which of the following is the most appropriate test in making the diagnosis?
Lower endoscopy
Bowel wall biopsy
CT scan of the abdomen
Stool ova and parasite assay
Stool ova and parasite assay
This patient who presents with persistent abdominal discomfort, nausea, bloating, diarrhea, eosinophilia, and signs of malabsorption (thin-appearing, vitamin D deficiency) in the setting of immigration from a resource-limited country most likely has a gastrointestinal parasite infection (Ascaris lumbricoides). The most appropriate next step in management is to obtain a stool ova and parasite assay.

Ascaris lumbricoides is a roundworm that is transmitted via the fecal-oral route (egg ingestion). While most patients are asymptomatic, there can be pulmonary and intestinal manifestations in the early and late phases, respectively. Pulmonary signs include dry cough, dyspnea, fever, and wheezing. Intestinal signs include abdominal discomfort, diarrhea, nausea, vomiting, malabsorption, and/or anorexia. The diagnosis should be suspected in patients with vague abdominal symptoms with travel history to an endemic area. The diagnosis is secured with stool microscopy for eggs or worms. Complications of this condition include intestinal obstruction or hepatobiliary/pancreatic involvement, presenting as biliary colic, obstructive jaundice, and/or ascending cholangitis. Treatment in patients with uncomplicated infection is with anti-helminth therapy (albendazole or mebendazole).

Parija et al. review the epidemiology of helminth infections globally. The authors note that many cases are caused by Ascaris species. They recommend prompt identification of these infections as they can cause lack of school attendance, anemia, and cognitive deficits if left untreated.

Incorrect Answers:
Answer A: Bowel wall biopsy is used in the diagnostic work-up of suspected Whipple disease, which presents with chronic diarrhea, malabsorption, weight loss, and joint symptoms (arthralgias). This disease is progressive over years and would be less likely in this patient with disease onset of 3 months.

Answer B: CT scan of the abdomen is used in the diagnostic work-up of small bowel obstruction, which presents as crampy abdominal pain, constipation, obstipation, and/or vomiting. Bowel obstruction is an acute process that would be unlikely in this patient with chronic symptoms. Although bowel obstruction is a complication of Ascaris infection, this patient has no signs of obstruction. Diarrhea may occur secondary to infection of the colon as well including colitis or diverticulitis; however, these conditions typically cause pain and low grade fever.

Answer C: Lower endoscopy (colonoscopy) is used in the diagnosis of inflammatory bowel disease, consisting of Crohn disease and ulcerative colitis. Ulcerative colitis presents with bloody diarrhea, abdominal pain, weight loss, and fatigue. Eosinophilia would be unexpected, and this patient does not have bloody diarrhea.

Answer E: Stool toxin assay is used to diagnose Clostridioides difficile infection. This presents after recent antibiotic use with watery diarrhea, dehydration, fever, and nausea. It presents acutely and generally without eosinophilia.

Bullet Summary:
Parasitic gastrointestinal infections present with chronic diarrhea, abdominal discomfort, malabsorption, and eosinophilia, and are diagnosed using stool ova and parasite assays.