This patient with dysentery most likely has Escherichia coli infection and is at risk for hemolytic uremic syndrome (HUS). E. coli O157:H7, a Shiga toxin–producing E. coli (STEC) serotype, is the most common cause of acute bloody diarrhea in the United States. It differs from other causes of dysentery in that fever is distinctly uncommon. STEC organisms are widespread in the gastrointestinal tract of domesticated animals, particularly cattle, and cause disease through ingestion of contaminated food or, as in this case, unpasteurized milk. One of the most serious complications of STEC infection is the development of HUS, which occurs in 5% to 10% of cases, most frequently in children. HUS is a form of thrombotic microangiopathy characterized by fever, hemolytic anemia, consumptive thrombocytopenia, neurologic findings, and kidney failure. Antibiotic and antimotility therapies are both associated with increased risk for HUS and should not be prescribed when there is clinical concern for STEC gastrointestinal disease.

The other choices are complications associated with bacterial causes of dysentery, but unlike STEC infections, these are usually associated with fevers. Aortitis is an inflammation of the aortic wall and can potentially be caused by Salmonella infection, which has a propensity for causing endovascular infection, particularly when there is significant atherosclerosis or graft material. Guillain-Barré syndrome is a rare complication of Campylobacter infection, occurring in less than 1% of cases; however, up to 40% of cases of Guillain-Barré are triggered by an antecedent Campylobacter infection. Several strains of Yersinia cause infection of the mesenteric lymph nodes and can mimic acute appendicitis. Grossly bloody stools are uncommon with Yersinia infection. Reactive arthritis can occur following Campylobacter, Shigella, Salmonella, or Yersinia infections in patients who are positive for the HLA-B27 gene.