An 8-year-old boy presents to the emergency department with a complaint of high-grade fever for 5 days. The mother complains that his urine output has been significantly less and he had several episodes of bloody diarrhea. On examination, the child is ill-looking, pale, and febrile with edema on both the extremities and crepitations in both lung bases. Laboratory investigations show low hemoglobin and platelet count. What is the most likely diagnosis?