The colitis caused by E. coli O157:H7 is characterized by severe abdominal cramps, diarrhea that typically turns bloody within 24 hours, and sometimes fever. The incubation period—that is, the time from exposure to the onset of symptoms—in outbreaks is usually reported as 3 to 4 days but may be as short as 1 day or as long as 10 days. Infection can occur in people of all ages but is most common in children.
Unlike other E. coli pathogens, which remain on intestinal surfaces, Shiga toxin-producing bacteria, like O157:H7, are invasive. After ingestion, E. coli bacteria rapidly multiply in the large intestine and then bind tightly to cells in the intestinal lining. Once in the systemic circulation, Shiga toxin becomes attached to weak receptors on white blood cells, thus allowing the toxin to “ride piggyback” to the kidneys.
Inflammation caused by the toxins is believed to be the cause of hemorrhagic colitis, the first symptom of E. coli infection, which is characterized by the sudden onset of abdominal pain and severe cramps. Such symptoms are typically followed within 24 hours by diarrhea, sometimes fever.
As the infection progresses, diarrhea becomes watery and then may become grossly bloody; that is, bloody to the naked eye. E. coli symptoms also may include vomiting and fever, although fever is an uncommon symptom.
On rare occasions, E. coli infection can cause bowel necrosis (tissue death) and perforation without progressing to hemolytic uremic syndrome (HUS)—a complication of E. coli infection that is now recognized as the most common cause of acute kidney failure in infants and young children. In about 10 percent of E. coli cases, the Shiga toxin attachment results in HUS.
Infection with E. coli O157:H7 or other Shiga toxin-producing E. coli is usually confirmed by the detection of the bacteria in a stool specimen from an infected individual. Most hospitals labs and physicians know to test for these bacteria, especially if the potentially infected person has bloody diarrhea. Still, it remains a good idea to specifically request that a stool specimen be tested for the presence of Shiga toxin-producing E. coli.
In most infected individuals, symptoms of a Shiga toxin-producing E. coli infection last about a week and resolve without any long-term problems. Antibiotics do not improve the illness, and some medical researchers believe that these medications can increase the risk of developing HUS. Therefore, apart from supportive care, such as close attention to hydration and nutrition, there is no specific therapy to halt E. coli symptoms. The recent finding that E. coli O157:H7 initially speeds up blood coagulation may lead to future medical therapies that could forestall the most serious consequences. Most individuals who do not develop HUS recover within two weeks.