O157H7

O157:H7 is a serotype of Escherichia coli defined by the O157 somatic antigen and the H7 flagellar antigen. It is a major member of the Shiga toxin–producing E. coli (STEC), also known as enterohemorrhagic E. coli (EHEC). O157:H7 is a prominent cause of hemorrhagic colitis and can lead to hemolytic uremic syndrome (HUS), particularly in children and older adults.

The primary reservoir for O157:H7 is ruminant animals, especially cattle. Humans usually acquire the infection through ingestion of contaminated food or water, or via contact with cattle or their environment. The infectious dose is low, with estimates ranging from tens to hundreds of organisms, making prevention and proper handling essential.

Virulence factors include Shiga toxins (Stx1 and Stx2), which inhibit protein synthesis and can contribute to systemic complications. Attachment and effacement of intestinal cells, mediated by intimin (the eae gene), cause characteristic intestinal damage. The combination of toxin production and adherent lesions underlies the disease spectrum.

Clinical presentation typically begins 1 to 10 days after exposure. Patients often develop sudden abdominal cramps, diarrhea that may become bloody, and little or no fever. A subset develops HUS, a serious complication involving microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury, particularly in children.

Diagnosis combines clinical suspicion with laboratory testing. Stool testing includes detection of stx genes by PCR and culture on selective media. O157:H7 colonies on sorbitol-MacConkey agar are usually non-sorbitol fermenters. Management is primarily supportive; antibiotics are used judiciously due to uncertain effects on toxin release.

Prevention focuses on proper cooking of ground beef and other foods, pasteurization, avoidance of cross-contamination, and thorough hand hygiene. Public health surveillance supports outbreak detection and response.