Most common cause of hemolytic uremic syndrome is –
**Core Concept**
Hemolytic uremic syndrome (HUS) is a complex disorder characterized by the triad of hemolytic anemia, acute kidney injury, and thrombocytopenia. It is often caused by a bacterial infection, particularly those that produce Shiga toxins, which damage the endothelial cells lining the blood vessels.
**Why the Correct Answer is Right**
The most common cause of HUS is E. coli O157:H7, a Shiga toxin-producing E. coli (STEC) strain. The Shiga toxin produced by this bacterium causes endothelial cell damage, leading to the activation of the coagulation cascade and the formation of microthrombi in the small blood vessels. This results in the characteristic hemolytic anemia, acute kidney injury, and thrombocytopenia seen in HUS. The toxin also causes the release of cytokines and the activation of the complement system, further contributing to the pathogenesis of HUS.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a particular organism or toxin that is known to cause HUS.
* **Option B:** This option is incorrect because it refers to a condition that is associated with HUS, but is not the most common cause.
* **Option C:** This option is incorrect because it refers to a different type of kidney disease that is not characterized by the triad of hemolytic anemia, acute kidney injury, and thrombocytopenia.
**Clinical Pearl / High-Yield Fact**
In patients with HUS, the presence of diarrhea is a key risk factor for the development of this condition. This is because the Shiga toxin produced by E. coli O157:H7 is often transmitted through contaminated food or water.
**Correct Answer: A. E. coli O157:H7**