Enterohemorrhagic Escherichia coli, or EHEC, is a specific group of bacteria that can cause severe illness in humans. While many E. coli strains are harmless, certain EHEC strains cause serious health issues. Understanding how these bacteria function and spread is important for public health, as infections can range from mild to life-threatening.
Understanding Enterohemorrhagic E. coli
EHEC is a distinct strain of Escherichia coli that causes severe infections. Its defining characteristic is the production of potent Shiga toxins (Stx1 and Stx2), which are responsible for severe symptoms. The most commonly recognized serotype is O157:H7, linked to numerous outbreaks of bloody diarrhea and hemolytic uremic syndrome (HUS) globally.
Shiga toxins bind to a specific receptor called globotriaosylceramide (Gb3) on human cells, particularly in the intestinal wall. Once bound, the toxins enter the cells and inhibit protein synthesis, leading to cell damage and death. This cellular disruption contributes to the severe gastrointestinal symptoms observed in infected individuals. While EHEC can colonize the gastrointestinal tract of animals like cattle without causing illness, humans are susceptible to the toxin’s effects due to Gb3 receptors on their vascular endothelium.
Sources of Infection and Transmission
EHEC infection primarily occurs through ingesting contaminated food or water. A common source is undercooked ground beef, which can be contaminated during slaughter. Contaminated produce like spinach, lettuce, and sprouts, as well as unpasteurized milk, apple juice, or apple cider, have been linked to outbreaks. These foods can become contaminated if they contact animal feces containing the bacteria.
Water can also serve as a vehicle for transmission, including swimming in or drinking water contaminated with EHEC, such as inadequately chlorinated pools, lakes, or untreated well water. Direct contact with animals, particularly ruminants like cattle, goats, and sheep, at petting zoos or farms, poses another risk, as these animals can carry EHEC asymptomatically and shed the bacteria. Person-to-person transmission is also possible, especially in settings like daycare centers or within families, due to the low infectious dose required.
Recognizing Symptoms and Potential Complications
Symptoms of EHEC infection typically begin two to five days after exposure, though they can appear as early as one or as late as ten days. The illness often starts with severe abdominal cramps. This is usually followed by watery diarrhea that often progresses to bloody diarrhea within 24 hours. Vomiting and nausea are also common, while fever is generally absent or low-grade.
The most serious complication is Hemolytic Uremic Syndrome (HUS), which develops in about 5% to 10% of infected individuals. HUS is a severe condition characterized by acute kidney failure, a low red blood cell count (hemolytic anemia), and a low platelet count (thrombocytopenia). Young children, especially those under five, and the elderly are at higher risk of developing HUS. Signs of HUS include decreased urination, extreme tiredness, pale skin, and unexplained bruising. HUS can lead to permanent kidney damage or be fatal.
Diagnosis and Management
Diagnosis of EHEC infection typically involves laboratory testing of stool samples. Healthcare providers look for E. coli bacteria, specifically serotypes like O157:H7, or the Shiga toxin it produces. Rapid stool assays or molecular tests detecting the gene encoding the Shiga toxin can help confirm the diagnosis. Stool samples should be collected early in the illness, ideally before any antibiotic treatment, to improve detection rates.
Management of EHEC infection is primarily supportive, focusing on hydration and rest. Patients with severe symptoms, particularly those developing HUS, often require hospitalization for close monitoring and care. Certain medications should be avoided: antibiotics are generally not recommended because they can increase Shiga toxin release, potentially worsening the condition or raising the risk of HUS. Similarly, anti-diarrheal medications should be avoided as they may prolong the presence of bacteria and toxins in the intestines, increasing the risk of systemic complications.
Preventive Measures
Preventing EHEC infection centers on good hygiene and safe food handling. Thorough handwashing with soap and running water is an effective preventive measure, especially after using the restroom, changing diapers, or handling animals. When soap and water are unavailable, an alcohol-based hand sanitizer with at least 60% alcohol can be used.
Proper food handling and cooking are important. Ground beef, pork, and lamb should be cooked to an internal temperature of at least 160°F (71°C) to destroy the bacteria. Preventing cross-contamination in the kitchen is important; raw meat should be kept separate from ready-to-eat foods, and surfaces, cutting boards, and utensils that have touched raw meat should be washed thoroughly. Consuming only pasteurized milk, dairy products, and juices helps avoid infection, as pasteurization kills harmful germs. When swimming, avoid swallowing water from lakes, ponds, streams, or pools. If using well water, boiling may be necessary if its safety is uncertain.