Enterohemorrhagic Escherichia coli (EHEC) is a group of E. coli bacteria that causes severe illness in humans. Unlike harmless strains, EHEC produces potent Shiga toxin, which damages the intestinal lining. Serotype O157:H7 is a well-recognized EHEC strain often responsible for outbreaks of bloody diarrhea and a serious complication called hemolytic uremic syndrome (HUS).
Sources of Infection
EHEC is primarily acquired through contaminated food or water. Cattle and other ruminants like sheep and goats are natural reservoirs for EHEC. Raw or undercooked meat, especially ground beef, is a common source. Contamination can occur during meat processing, and affected meat often looks and smells normal. Unpasteurized dairy products (e.g., raw milk) and juices (e.g., apple cider) also pose a risk.
Contaminated raw vegetables, including leafy greens and sprouts, can carry the bacteria if they contact animal feces or contaminated water. Swimming in or drinking contaminated water, such as from lakes or pools, can also lead to infection. Person-to-person transmission is possible, especially in settings like daycare centers, typically through the fecal-oral route due to inadequate handwashing. Direct contact with infected animals or their environments, such as at petting zoos, is another pathway for transmission.
Symptoms and Progression
The incubation period for EHEC infection ranges from 3 to 4 days, though it can be 1 to 10 days. Initial symptoms often include severe abdominal cramps and watery diarrhea. Fever is usually absent or low-grade during this phase.
Within about 24 hours, the illness commonly progresses to bloody diarrhea, known as hemorrhagic colitis. Some patients report diarrhea that is almost entirely blood. Most uncomplicated infections resolve within 1 to 8 days, but progression to bloody stools is a characteristic sign. Dehydration, fatigue, and nausea may also be present.
Serious Complications
Hemolytic Uremic Syndrome (HUS) is a serious complication of EHEC infection that affects the blood and kidneys. It is characterized by hemolytic anemia (low red blood cells), thrombocytopenia (low platelet count), and acute kidney injury. The Shiga toxin produced by EHEC directly damages blood vessels, particularly in the kidneys, leading to these issues.
HUS develops 5 to 10 days after diarrheal symptoms begin, often as diarrhea improves. Children under 5 and the elderly are at highest risk, with up to 12.9% of children under 5 experiencing this complication. Warning signs of HUS appearing after the initial diarrheal phase include decreased or no urination, unexplained bruising or tiny red spots on the skin, and loss of pink color in the skin and lower eyelids (indicating anemia). Affected individuals may also experience extreme tiredness, irritability, or decreased awareness. HUS can lead to severe outcomes, including kidney failure, neurological problems (e.g., seizures or stroke), and can be fatal.
Diagnosis and Treatment
Diagnosis of EHEC infection involves laboratory testing of a stool sample to identify the bacteria or to detect the Shiga toxin. Molecular tests, such as real-time PCR, can also identify the genes encoding the Shiga toxin. Identifying the specific EHEC serotype, like O157:H7, helps in understanding the source of outbreaks.
Treatment for EHEC infection is primarily supportive, focusing on managing symptoms and preventing complications. Maintaining proper hydration is important, often through oral fluids, to counteract fluid loss from diarrhea. Patients, especially children, are monitored closely for signs of HUS, including changes in urine output or paleness.
Antibiotics are not recommended for EHEC infections because they may increase the risk of HUS. This is believed to occur because antibiotics can cause bacteria to release more Shiga toxin as they are destroyed. Anti-diarrheal medications are also avoided as they can slow the digestive system, potentially preventing toxin expulsion and increasing systemic complication risk. In severe HUS cases, hospitalization may be necessary, with treatment involving intravenous fluids, blood transfusions, and kidney dialysis.
Prevention Methods
Preventing EHEC infection involves several practical steps to minimize exposure to the bacteria. Thorough handwashing with soap and running water is a primary defense, especially after using the bathroom, changing diapers, or handling animals. Hands should also be washed before preparing or eating food.
Cooking ground meat, particularly beef, to a safe internal temperature is important, as EHEC can be present even in meat that looks and smells normal. Using a food thermometer can confirm that ground beef reaches 160°F (71°C). Avoiding cross-contamination in the kitchen by keeping raw meat separate from other foods and washing cutting boards, utensils, and countertops after contact with raw meat prevents the spread of bacteria.
Washing all fruits and vegetables thoroughly, especially those eaten raw, helps remove surface contaminants. Consuming only pasteurized milk and juices is also a safeguard, as pasteurization kills harmful bacteria like EHEC. Avoiding swallowing water when swimming in lakes, ponds, or untreated pools further reduces risk.