Diarrhoeagenic E. coli Infection

Escherichia coli is normally a commensal organism of the gastrointestinal tract, but specific pathotypes have acquired virulence factors enabling them to cause diarrhoeal disease through distinct mechanisms, with the specific pathotype determining the clinical picture, the appropriate diagnostic approach and, critically, whether antibiotic therapy is safe or actively contraindicated.

Classification by pathotype

• Enterotoxigenic Escherichia coli produces heat labile and heat stable enterotoxins causing secretory watery diarrhoea, and is the leading bacterial cause of traveller's diarrhoea worldwide.
• Enteropathogenic Escherichia coli causes attaching and effacing lesions on the intestinal epithelium, producing watery diarrhoea predominantly in infants and young children in resource limited settings.
• Enteroinvasive Escherichia coli invades colonic epithelium in a manner mechanistically similar to Shigella, producing a dysenteric, invasive picture with fever and bloody stool.
• Enteroaggregative Escherichia coli adheres to the intestinal mucosa in a characteristic stacked brick pattern, causing persistent watery diarrhoea, particularly recognised in children and in HIV positive patients.
• Shiga toxin producing Escherichia coli (including the well recognised serotype O157:H7 and other non O157 serotypes) produces Shiga toxin, causing haemorrhagic colitis and carrying the specific and serious risk of progression to haemolytic uraemic syndrome, a distinction of critical importance for management.

• Enterotoxigenic Escherichia coli presents with watery, non bloody diarrhoea, abdominal cramping and low grade fever, developing one to three days after exposure, typically in the context of travel to a resource limited setting.
• Shiga toxin producing Escherichia coli classically presents with severe abdominal cramping followed by watery diarrhoea that becomes grossly bloody over one to two days, often without significant fever, following an incubation period of three to four days, most frequently linked to undercooked ground beef, unpasteurised dairy products or contaminated leafy vegetables.
• Features that should specifically raise concern for Shiga toxin producing Escherichia coli and prompt avoidance of antimotility agents and antibiotics include grossly bloody diarrhoea, severe abdominal pain out of proportion to other findings, and a compatible food exposure history.
• Warning signs of evolving haemolytic uraemic syndrome, typically appearing five to ten days after diarrhoea onset, include pallor, reduced urine output, oedema, lethargy and petechiae, and require urgent assessment given the risk of acute kidney injury, microangiopathic haemolytic anaemia and thrombocytopenia.
• Enteroaggregative Escherichia coli produces a more protracted, sometimes weeks long, watery diarrhoeal illness, occasionally with low grade mucus and blood, and is an important consideration in persistent diarrhoea, particularly in children and in HIV positive patients.

• Stool culture with specific request for Shiga toxin producing Escherichia coli screening (since routine stool culture protocols do not always reliably isolate this organism, given that O157:H7 typically does not ferment sorbitol, which is exploited in selective media, while non O157 serotypes require specific Shiga toxin enzyme immunoassay or polymerase chain reaction testing to be reliably identified) is essential in any patient with bloody diarrhoea.
• Multiplex polymerase chain reaction stool panels, where available, provide rapid pathotype specific identification across the diarrhoeagenic Escherichia coli group and distinguish these from other bacterial, viral and parasitic causes.
• Full blood count, blood film, renal function, and lactate dehydrogenase should be checked and monitored closely in any patient with confirmed or strongly suspected Shiga toxin producing Escherichia coli infection, actively screening for the early haematological and renal changes of evolving haemolytic uraemic syndrome (schistocytes on film, falling platelet count, rising creatinine) even before overt clinical features develop.
• Diagnosis of the other diarrhoeagenic pathotypes rests on specific stool culture serotyping or molecular testing, generally reserved for prolonged, severe, outbreak related or epidemiologically significant presentations rather than routine self limiting illness.

• Oral rehydration therapy, with intravenous rehydration reserved for significant dehydration, forms the foundation of management across all pathotypes, following the principles detailed under gastroenteritis generally.
• Antibiotics and antimotility agents (loperamide) must be avoided in confirmed or suspected Shiga toxin producing Escherichia coli infection, given robust evidence that both increase the risk of subsequent haemolytic uraemic syndrome, believed to reflect increased bacterial toxin release with antibiotic induced bacterial lysis and prolonged toxin exposure with reduced gut transit from antimotility agents.
• Any patient with bloody diarrhoea should be managed supportively pending stool culture results and should not receive empirical antibiotics or antimotility agents until Shiga toxin producing Escherichia coli has been reasonably excluded.
• Traveller's diarrhoea caused by enterotoxigenic Escherichia coli in adults may be treated with azithromycin 1000 mg orally as a single dose, or 500 mg once daily for three days, particularly favoured given rising fluoroquinolone resistance in many endemic regions, or with ciprofloxacin 500 mg twice daily for three days where local resistance patterns support its use, reserved for moderate to severe illness rather than given routinely for mild, self limiting disease.
• Established or evolving haemolytic uraemic syndrome requires urgent nephrology and, in children, paediatric nephrology involvement, with supportive management of acute kidney injury including careful fluid balance, correction of electrolyte disturbance, blood product transfusion guided by clinical status rather than numerical thresholds alone given the risk of exacerbating microangiopathy, and renal replacement therapy where indicated, managed within a specialist unit given the complexity and potential severity of this complication.
• Enteroinvasive and enteroaggregative Escherichia coli causing severe, prolonged or systemic illness may warrant targeted antibiotic therapy guided by culture and susceptibility results, following principles similar to those used for Shigella, though routine antibiotic treatment of mild, self limiting presentations is not recommended.
• Prevention through food safety measures, including thorough cooking of ground beef, avoidance of unpasteurised dairy products, and careful washing of fresh produce, together with strict hand hygiene, remains the most effective strategy given the absence of a specific vaccine for any diarrhoeagenic Escherichia coli pathotype.