Review Question - QID 213634

An 18-year-old girl is brought into the emergency department by her parents for diarrhea over the past 5 days. She reports that after eating at a barbecue she developed diarrhea. At first, she thought it was just the “stomach flu” and didn’t think too much of it. However, 2 days ago she began developing intense abdominal cramps and bloody diarrhea. She endorses lethargy, nausea, and 1 pre-syncopal episode but denies fever, confusion, hematemesis, or neurologic deficits. Laboratory studies are shown below. A physical examination demonstrates diffuse abdominal tenderness, conjunctival pallor, and delayed capillary perfusion. Figure A shows the results of the patient’s peripheral smear.

Hemoglobin: 9.1 g/dL
Hematocrit: 30 %
Leukocyte count: 16,000/mm^3 with neutrophilic predominance
Platelet count: 87,000/mm^3

Serum:
Na+: 137 mEq/L
Cl-: 96 mEq/L
K+: 4.1 mEq/L
HCO3-: 25 mEq/L
BUN: 17 mg/dL
Glucose: 130 mg/dL
Creatinine: 2.5 mg/dL
Thyroid-stimulating hormone: 2.1 µU/mL
Ca2+: 9.1mg/dL
AST: 8 U/L
ALT: 12 U/L

What is the underlying etiology for this patient’s condition?