What is the most likely associated condition for a 3-year-old girl presenting with fever, elevated blood pressure, and a peripheral blood smear showing Gram-negative rods?

The presentation of a 3-year-old girl with fever, elevated blood pressure, and a peripheral blood smear showing Gram-negative rods strongly suggests an infection that may lead to serious complications, particularly those associated with hemolytic uremic syndrome (HUS).

HUS is characterized by a triad of symptoms: hemolytic anemia, acute renal failure, and thrombocytopenia. It is often related to infection with certain strains of Escherichia coli, particularly Enterohemorrhagic E. coli (EHEC), which can produce toxins leading to endothelial damage and subsequent development of HUS. The presence of Gram-negative rods in the blood smear aligns with this likely infectious agent, while the fever indicates an active infection that could precipitate HUS.

In contrast, acute lymphoblastic leukemia usually presents with more varied symptoms including fatigue, frequent infections due to bone marrow infiltration, and other hematological abnormalities, but not typically with Gram-negative rods in the blood smear. Thalassemia is a blood disorder resulting in abnormal hemoglobin but would not typically present with an acute infection or related elevated blood pressure and peripheral smear finding as described. Viral infections can also cause fever but would not usually produce Gram-negative bacteria observed on a blood