Hemolytic uremic syndrome is most commonly associated with infection by which organism?

• A. Salmonella Typhi
• B. E. coli O157:H7
• C. Vibrio cholerae
• D. Yersinia enterocolitica

Answer: (B)

HUS is driven by damage to small vessel endothelium in the kidneys, leading to microangiopathic hemolytic anemia, low platelets, and acute kidney injury. The most common trigger in children is infection with Shiga toxin–producing Escherichia coli, especially the O157:H7 serotype. The Shiga-like toxin released by this bacteria injures endothelial cells, promoting platelet activation and the formation of microthrombi in renal vessels. As red blood cells pass through these narrowed, damaged vessels, they are sheared, causing hemolysis, while platelets are consumed, producing thrombocytopenia; kidney involvement is prominent due to the toxin’s strong effect on renal microvasculature.

The other organisms listed cause distinct diarrheal or systemic diseases (typhoid fever with Salmonella Typhi, classic cholera with Vibrio cholerae, or enteric Yersinia infections) and are not the typical triggers of HUS via Shiga toxin–mediated endothelial injury. While HUS can rarely follow other Shiga-toxin producers, the association with E. coli O157:H7 is the strongest and most well-established.