What symptom is frequently associated with E. coli infections?

Bloody diarrhea is a hallmark symptom of E. coli infections, particularly those caused by the strain known as Enterohemorrhagic E. coli (EHEC), which includes O157:H7. This specific strain produces toxins that can cause severe damage to the intestinal lining, resulting in inflammation, bleeding, and the characteristic bloody stools. This symptom is significant because it can lead to serious complications, such as hemolytic uremic syndrome (HUS), particularly in vulnerable populations.

In contrast, while fever can occur in some cases, especially if the infection is more severe or systemic, it is not as specific or common as bloody diarrhea. Similarly, headaches can be associated with various infections and are not uniquely linked to E. coli. Cough is typically associated with respiratory infections and does not relate to gastrointestinal conditions such as those caused by E. coli. Therefore, bloody diarrhea stands out as the primary and most recognizable symptom associated with E. coli infections.