Overview
Enteric infectious diseases caused by enterohemorrhagic Escherichia coli (EHEC), the causative agent of hemorrhagic enteritis, mainly Escherichia coli O157:H7, a diarrhea-causing Escherichia coli bacterium newly discovered in 1982. In addition, O26:H11 may also be one of the pathogens, which has not been officially reported in China.
Epidemiology
Poultry and livestock are the storage hosts of the disease and the main source of infection, such as cattle, sheep, swine, etc. Cattle have the highest carrier rate. Patients and asymptomatic carriers are also a source of infection. Digestive tract transmission, through eating contaminated food and water or contact with patients and infected. Commonly contaminated foods are beef, milk, beef liver, chicken, lamb, vegetables and fruits, etc. The population is generally susceptible, but the elderly, children are mainly. There are obvious seasonal 7, 8, 9 months for the epidemic peak. The mass production, refrigeration, transportation and supply of fast food can easily lead to large-scale outbreaks of food poisoning; it can also be distributed. The disease is globally distributed, and the incidence of the disease is on the rise in regions and countries where sanitary conditions are better and most enteric infections have been basically controlled.
Causes
Escherichia coli O157: H7 is different from other serotypes of Escherichia coli, in 30 ~ 42 ℃ growth are good, but the optimal growth temperature is still 37 ℃, slow fermentation of sorbitol – MacConkey (SMAC) medium can be used as a screening medium for O157: H7. In SMAC medium, O157: H7 colonies were colorless, while the fermentation strains were pink, but half of EPEC strains have similar characteristics to O157: H7, attention should be paid to the identification of EPEC and EHEC. Escherichia coli O157: H7 acid-resistant low temperature, pH 2.5 ~ 3.5, temperature 37 ℃, can withstand 5h without losing activity, in the refrigerator can survive for a long time not heat-resistant, 75 ℃ 1min that is killed. Escherichia coli O157:H7 does not contain the general enterotoxin gene code, with gene probes and animal testing do not produce LTST, not invasive, does not belong to the EPEC serotypes can produce a large number of Shiga-like toxin (Shiga-Liketoxin, referred to as SLT).SLT antigenic, can be Shiga type I bacterial toxin rabbit antisera and neutralization of SLT because it can make the SLT has antigen, can be neutralized by rabbit antiserum of Shiga type I bacterial toxin, because SLT can make Vero cells (i.e., African green monkey kidney cells) degenerate and dissolve and die, so it is also called Veto toxin, abbreviated as VT. It can be inactivated by heating at 98℃ for 15min. According to different antigenicity, it is divided into VT1 and VT2. Structurally, they are composed of 1 A subunit and 5-6 B subunits, with molecular weights of 3300 and 8000 respectively. Pathogenesis: EHEC invades the human body from the oral cavity, and after reaching the intestinal lumen, it adheres to the brush edge of intestinal villi with the help of bacterial hairs in a restricted manner. The A subunit has toxin activity, enters the cell and inhibits protein synthesis, damaging the intestinal epithelium, with a focus on the cecum and colon, and diffuse hemorrhagic ulceration of the intestinal mucosa can be seen by naked eye. In addition to the intestinal epithelium, the GB3 receptor is also widely present in vascular endothelial cells, kidney, and neural tissue cells. Damage to vascular endothelial cells, erythrocytes, and platelets leads to HUS and widespread tubular necrosis, which can lead to acute renal failure. Vero toxin also stimulates the release of factor VIII from endothelial cells, resulting in thrombotic thrombocytopenic purpura.
Symptoms
The incubation period of the disease is 3 to 8 days. Abdominal cramps and diarrhea develop, and some may progress to bloody diarrhea, i.e., hemorrhagic enterocolitis, which may be accompanied by fever, nausea, and vomiting. Most patients recover within 10 days. Some sporadic infections may progress to hemolytic uremic syndrome (HUS), which is characterized by acute renal failure, microvascular hemolytic anemia and thrombocytopenia, and in some cases central nervous system complications, such as epilepsy, lethargy and coma.
Examination
1. Laboratory examination
(1) Bacterial culture and isolation: Increasing the positive rate of stool culture can increase the diagnosis rate. Factors affecting the culture are mainly the character of stool, the duration of the disease and the choice of culture medium. The main factors affecting the culture are the nature of the stool, the duration of the disease and the choice of culture medium. Bloody stools and short duration of the disease have a high positivity rate, while watery stools and long duration of the disease, especially more than 7 days, have a low positivity rate Sorbitol-McConkey agar (SMAC) can increase the positivity rate.
(2) Immunological testing Direct ELISA reaction with monoclonal antibodies to detect O157:H7 E. coli.
(3) Genetic testing The application of EHEC-specific DNA probe, its sensitivity and specificity can reach 99%; or the application of PCR to EHEC DNA sequence analysis found that its hemolysin AB gene is unique to EHEC, which is specific, sensitive and fast, and the results can be obtained in 3 to 4h. There are other multiplex PCR methods for simultaneous amplification of two pairs of oligonucleotide primers for SLT1 and SLT2, but they have not yet been widely used in clinical practice. Genetic testing can be used for clinical research and epidemiological investigation.
2. Other auxiliary tests
X-ray examination, mucin, deoxyribonucleic acid staining, platelets, plasma HCO3-concentration test, etc.
Diagnosis
In addition to the support of epidemiology and clinical features, O157:H7 Escherichia coli and its toxin can be found from the stool to confirm the diagnosis, and its identification methods are:
1. Bacterial culture isolation
Improve the positive rate of stool culture can improve the rate of confirmation of the diagnosis of factors affecting the culture, mainly stool traits, the duration of the disease and the choice of culture medium. Bloody stool, short duration of the disease, the positive rate is high; watery stool, long duration of the disease, especially more than 7 days, the positive rate is low Sorbitol-McConkey agar (SMAC) can improve the positive rate.
2. Immunological detection
Direct ELISA with monoclonal antibody to detect Escherichia coli O157:H7.
3. Genetic testing
Apply EHEC specific DNA probe whose sensitivity and specificity can reach 99%; or apply PCR to analyze the DNA sequence of EHEC, and find that its hemolysin AB gene is unique to EHEC, which is specific, sensitive and fast, and the result can be obtained in 3~4h.
Differential diagnosis
It should be differentiated from other Escherichia coli enteritis.
Complications
Complication of hemolytic uremic syndrome or thrombotic thrombocytopenic purpura Diagnosis: In addition to epidemiology and clinical features support, O157: H7 Escherichia coli and its toxin can be found from the stool to confirm the diagnosis, and its identification methods are:
1. Bacterial culture isolation to improve the positive rate of stool culture can improve the rate of confirmation of the diagnosis of the factors affecting the culture, mainly stool traits, the duration of the disease and the choice of culture medium. Bloody stool, short duration of the disease, the positive rate is high; watery stool, long duration of the disease, especially more than 7 days, the positive rate is low Sorbitol-McConkey agar (SMAC) can improve the positive rate.
2. Immunological testing: Direct ELISA reaction with monoclonal antibodies to detect O157:H7 E. coli.
3. Genetic testing using EHEC-specific DNA probe whose sensitivity and specificity can reach 99%; or applying PCR to analyze the sequence of EHEC DNA, and found that its hemolysin AB gene is unique to EHEC, which is specific, sensitive and fast, and the results can be obtained in 3~4 hours. There are other multiplex PCR methods for simultaneous amplification of two pairs of oligonucleotide primers for SLT1 and SLT2, but they have not yet been widely used in clinical practice. Genetic testing can be used for clinical research and epidemiologic investigation.
Treatment
Whether antimicrobials should be used is not yet academically conclusive. In principle, it can be treated as other infectious diarrhea, and antibiotics should be used in severe cases, such as sparfloxacin (sparfloxacin), berberine, etc.; in mild cases, intestinal mucosal protector hexagonal montmorillonite or microecological regulator can be used. At the same time, pay attention to correcting dehydration and strengthening supportive therapy. If combined with HUS, rescue according to HUS.
Prevention
The prevention of this disease, in addition to the common features with other intestinal infectious diseases, such as washing hands before and after meals to protect the hygiene of food and water sources, the focus should be to strengthen the management of frozen fast food, to prevent the food from being contaminated, and to be sufficiently heated before consumption.
Prognosis
There have been disseminated cases in China, mild cases can be self-cured, serious comorbidities can lead to death.