What is the most likely diagnosis for a child presenting with oliguria, petechiae, and jaundice following bloody diarrhea?

The clinical presentation described—oliguria, petechiae, jaundice, and a recent history of bloody diarrhea—strongly suggests a diagnosis of hemolytic uremic syndrome (HUS) secondary to infection with E. coli O157:H7. This particular strain of E. coli is notorious for producing a Shiga toxin, which can lead to gastrointestinal symptoms including bloody diarrhea.

In the aftermath of the gastrointestinal infection, HUS can develop, particularly in children. It is characterized by the triad of acute renal failure (resulting in oliguria), hemolytic anemia (which can cause jaundice due to the breakdown of red blood cells), and thrombocytopenia (which may manifest as petechiae due to bleeding). The constellation of symptoms in this case aligns with HUS very well, making it the most likely diagnosis.

Acute kidney injury due to dehydration, while possible, would not typically present with the systemic symptoms such as jaundice and petechiae. Acute glomerulonephritis could present with hematuria and renal failure, but would not generally follow a bloody diarrhea illness and does not usually present with the combination of symptoms found here. Nephrotic syndrome is characterized by significant proteinuria