Initial symptoms of E. coli O157:H7 infection

The initial symptoms of E. coli O157:H7 infection usually appear about 3 to 5 days (though occasionally in as few as one day or as many as 10 days) after a person ingests the bacteria; the symptoms include

• nausea
• vomiting
• stomach cramps
• diarrhea that often is bloody

The person may have a mild fever of about 100 to 101F (37.7 to 38.3 C). These symptoms can be seen in infected children and adults.

Later symptoms  E. coli O157:H7 infections

The majority of people (especially normal adults) that get the infection resolve the infection without antibiotics in about five to 7 days. However, some people (about 10% of people infected, especially children under the age of 5 and the elderly) develop more severe signs and symptoms, and these people usually require hospitalization and aggressive treatment. These patients develop the usual symptoms listed above, but do not resolve the infection. They develop symptoms that last longer (at least a week) and, if not treated promptly, the infection may lead to disability or death.

These symptoms or complications fall into three main categories;

• Hemorrhagic (bloody) diarrhea: Hemorrhagic (bloody) diarrhea symptoms are an increased amount of blood in the diarrheal stool that does not seem to resolve and is usually accompanied by severe abdominal pain. Although this may resolve within a week, some individuals can develop anemia and dehydration that can cause death.
• Hemolytic-uremic syndrome (HUS): Hemolytic-uremic syndrome symptoms of pallor (due to anemia), fever, bruising or nose bleeding (due to destruction of blood platelets that are needed for blood to clot), fatigue, shortness of breath, swelling of the body, especially hands and feet, jaundice, and reduced flow of urine may be seen. HUS symptoms usually develop about 7 to 10 days after the initial diarrhea begins. HUS is the most common cause of kidney failure in children; children under 10 years old are the most likely to develop HUS. E. coli 0157:H7 produces toxins that damage the kidneys and destroys platelets that can lead to kidney failure, excessive bleeding, seizures or death.
• Thrombotic thrombocytopenic purpura (TTP): Thrombotic thrombocytopenic purpura is caused by the loss of platelets; however, the symptoms that occur are somewhat different and occur mainly in the elderly. The symptoms are fever, weakness, easy, rapid or "spontaneous" bruising, renal failure, and mental impairment that can rapidly progress to organ failures and death. Until the 1980's, TTP was considered a fatal disease, but since the 1980's, plasma exchange and infusion techniques have reduced the death rate in TTP patients to about 10%.

How is an infection with E. coli 0157:H7 diagnosed?

The diagnosis of E. coli 0157:H7 infection begins with an accurate history, physical exam, and an analysis of a sample of stool from the patient. A presumptive diagnosis is frequently made if the patient has symptoms of bloody diarrhea and a history of being exposed to persons, foods or liquids known to be a source of an E. coli 0157:H7 outbreak.

Because other disease-causing bacteria (for example, Shigella and Salmonella) can give patients similar initial symptoms, a definite diagnosis is based on culture of E. coli 0157:H7 from the patient's sample of stool on special culturing plates that then are tested with antiserum (antibodies) that react only with E. coli O157H7. Not all clinics or hospitals have the diagnostic antiserum, so the testing may take a few days.

Because of the high frequency of outbreaks of E. coli 0157:H7, the CDC in 2009 recommended that all patients being screened for community-acquired diarrheal infections have their stool samples analyzed with antisera for Shiga toxins, the toxins that are produced by E. coli 0157:H7 and a few other bacteria, in addition to having cultures of their stool. This approach may result in faster diagnosis of E. coli )157H7 infections.

Blood tests such as a complete blood count (CBC), and blood levels of electrolytes, platelets, blood urea nitrogen (BUN), and creatinine (blood tests that measure function of the kidney) are performed periodically to look for the development of HUS or TTP.

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