Enterohemorrhagic Escherichia coli infection

　　1. Etiology

　　Escherichia coli O157:H7 is different from other serotypes of Escherichia coli, which grows well at temperatures between 30 to 42°C, but the optimal growth temperature is still 37°C. The delayed fermentation sorbitol-MacConkey (SMAC) medium can be used as a selective medium for O157:H7. On the SMAC medium, O157:H7 colonies are colorless, while the fermented strains are pink, but half of the EPEC strains have similar characteristics to O157:H7, and attention should be paid to the differentiation between EPEC and EHEC. Escherichia coli O157:H7 is acid and cold-resistant, and can tolerate 5 hours without losing activity at pH 2.5 to 3.5 and temperature 37°C, and can survive for a long time in the refrigerator. It is not heat-resistant and can be killed by 75°C in 1 minute. Escherichia coli O157:H7 does not contain the general enterotoxin gene codon, and does not produce LT, ST through gene probe and animal tests, so it does not have invasiveness and does not belong to the EPEC serotype, and can produce a large amount of Shiga-like toxin (Shiga-Like toxin, abbreviated as SLT). SLT has antigenicity and can be neutralized by rabbit antiserum of Shigella type I toxin. Because SLT can denature, dissolve, and kill Vero cells (i.e., African green monkey kidney cells), it is also called Veto toxin, abbreviated as VT. Among the toxins produced by bacteria, VT is one of the strongest toxins. It can be inactivated by heating to 98°C for 15 minutes. According to the antigenicity, it is divided into VT1 and VT2. Structurally, they are both composed of 1A subunit and 5 to 6B subunits. The molecular weights are 3300 and 8000, respectively.

　　2. Pathogenesis

　　EHEC enters the human body through the oral cavity, reaches the intestinal lumen, and attaches locally to the brush border of intestinal villi with the help of pili. The B subunit binds to the intestinal epithelial cell glycolipid receptor GB3, and the A subunit has toxic activity, enters the cell and inhibits protein synthesis, damaging intestinal epithelial cells, with the cecum and colon being the focus. Grossly visible diffuse hemorrhage and ulcers of the intestinal mucosa. In addition to intestinal epithelial cells, the GB3 receptor is widely present in vascular endothelial cells, renal and nervous tissue cells, damaging vascular endothelial cells, red blood cells, and platelets, leading to HUS. Widespread tubular necrosis can lead to acute renal failure. The excitability of the parasympathetic nervous system is enhanced due to the action of toxins, which may result in sinus bradycardia and convulsions. Vero toxin also stimulates the release of factor VIII by endothelial cells, leading to thrombotic thrombocytopenic purpura.

　　Complications such as hemolytic uremia or thrombotic thrombocytopenic purpura. The lips may turn cherry red, and there may be a ketone odor in the breath. Severe cases may present with restlessness, drowsiness, coma, convulsions, and even shock. Significant hypokalemia symptoms often appear after 1 week of diarrhea, with severe cases developing soft paralysis, even respiratory muscle paralysis, arrhythmia, and coma, which may be life-threatening. The skin may be difficult to recover after scratching, blood pressure may drop, microcirculatory disorders may occur, muscle spasms, pulse may be weak, and oliguria or anuria may occur.

　　The incubation period is 1 to 14 days, commonly 4 to 8 days. Before the onset of the disease, there may be a history of consuming refrigerated ready-to-eat processed fast food. There are three clinical types: asymptomatic infection, mild diarrhea, and hemorrhagic colitis. The typical manifestation is an acute onset, diarrhea, initially watery stools, followed by bloody stools, accompanied by spastic abdominal pain, without fever or low fever, which may be accompanied by nausea, vomiting, and symptoms similar to upper respiratory tract infection. Without complications, the disease naturally heals in 7 to 10 days. A few patients may develop acute hemolytic uremic syndrome in the 1st to 2nd week of the disease, with symptoms such as pallor, weakness, hematuria, oliguria, anuria, subcutaneous and mucosal bleeding, jaundice, coma, convulsions, etc., which are more common in the elderly, children, and individuals with weakened immune function, with a mortality rate of 10% to 50%.

　　Poultry and livestock, such as cattle, sheep, and pigs, are the reservoir hosts and main sources of infection for this disease, with the highest bacterial carriage rate in cattle. Patients and asymptomatic carriers are also among the sources of infection. Transmission occurs through the digestive tract, which involves infection through contaminated food, water, or contact with patients. Commonly contaminated foods include beef, milk, beef liver, chicken, mutton, vegetables, and fruits. The population is generally susceptible, but the elderly and children are primarily affected. The disease has a distinct seasonal pattern, with July, August, and September being the peak months. The large-scale production, refrigeration, transportation, and supply of fast food are highly conducive to large-scale outbreaks of food poisoning; it can also occur sporadically. The disease is globally distributed, and in regions and countries with better hygiene conditions and where most intestinal infectious diseases have been basically controlled, the incidence rate of the disease is rising.

　　1. Bacterial culture isolation can improve the positive rate of stool culture and thus improve the diagnostic rate. Factors affecting culture include stool characteristics, course of disease, and selection of culture medium. Bloody stools, with a short course of disease, have a high positive rate; watery stools, with a long course of disease, especially those over 7 days, have a low positive rate. Sorbitol-MacConkey agar (SMAC) can improve the positive rate.

　　2. Immunological detection uses monoclonal antibodies to perform direct ELISA reaction to detect O157:H7 Escherichia coli.

　　3. Gene detection uses EHEC-specific DNA probes, with sensitivity and specificity both reaching 99%; or PCR is used to analyze the EHEC DNA sequence, finding that the hemolysin AB gene is unique to EHEC, with strong specificity, rapid sensitivity, and results can be obtained within 3-4 hours. There are also multiple PCR methods that simultaneously amplify the two pairs of oligonucleotide primers SLT1 and SLT2, but they have not been widely used in clinical practice. Gene detection can be used for clinical research and epidemiological surveys.

　　4. X-ray examination shows submucosal edema of the ascending colon and sigmoid colon.

　　Prognosis: There have been sporadic cases in China, with mild cases being self-limiting and severe complications leading to death. Patients' diet should be light and easy to digest, with more vegetables and fruits, reasonable dietary搭配, and attention should be paid to sufficient nutrition. In addition, patients should also pay attention to avoiding spicy, greasy, and cold foods.

　　Western medicine treatment for Enterohemorrhagic Escherichia coli infection

　　Medication:There is no academic consensus on whether antibiotics should be used. Some scholars propose that antibiotics cannot shorten the course of the disease, cannot reduce the occurrence of complications, and may even promote the release of Veto toxins, leading to the occurrence of HUS, therefore, it is proposed to avoid the use of antibiotics. However, some scholars propose that antibiotics can be used according to the principle of treating severe infections similar to other infectious diarrhea, such as ciprofloxacin (sparfloxacin), berberine, etc.; for mild cases, intestinal mucosal protectants such as attapulgite or microbiological regulators can be used. At the same time, attention should be paid to correct dehydration and strengthen supportive therapy. Patients with HUS should be rescued according to the抢救 protocol for HUS.