Approach
The presentation of foodborne Escherichia coli infection is similar to most other gastrointestinal infection. A thorough history is therefore integral to establishing a diagnosis as there are no definitive diagnostic clinical findings.
Stool cultures can confirm the diagnosis, with serotyping used to identify the exact strain (e.g., E coli O157:H7). CDC: E. coli (Escherichia coli) – resources for clinicians and laboratories Opens in new window
History
E coli incubation period varies according to aetiological agent; it may be as little as 6-48 hours for E coli (ETEC) or between 1-10 days (usually 3-4) for E coli O157:H7.[33]
Patients present with gastroenteritis symptoms including diarrhoea (principal symptom), abdominal pain/discomfort, anorexia, and nausea; vomiting is uncommon. Systemic symptoms, including lethargy or fever, may be present.
Enterohaemorrhagic E coli (EHEC) and enterotoxigenic E coli (ETEC) have more specific clinical presentations. ETEC infection typically causes profuse watery diarrhoea, while the Shiga-like toxin in EHEC causes bloody diarrhoea and abdominal pain.[31]
The history is important to identify risk factors and the causative agent. Although food history is important, this is unlikely to differentiate E coli infection from other causes of foodborne infection. A history of ingesting ground beef (e.g., in hamburgers) is important as there is a close association between ground beef and the O157:H7 subtype of E coli.[14]
One meta-analysis found that beef was the most significant food item risk for acquiring shiga-toxin producing E coli infection in North America and Europe, while chicken was the most significant food item in the Western Pacific.[34]
Travel history should always be sought as E coli is the most common cause of traveller's diarrhoea. Differences in acquisition of certain subtypes seem to be regional.[34] Contact history should be sought in all patients.
It is important to note that young children (<5 years), older people (>60 years), and those who are immunocompromised are more likely to deteriorate clinically as a consequence of E coli infection.
Physical examination
There are no pathognomonic features to differentiate patients with E coli gastroenteritis from those with other foodborne illnesses.[31] Fever and non-specific abdominal tenderness are common physical findings in patients with infectious diarrhoeal illnesses. Patients should be monitored for signs of volume depletion and potential haemodynamic compromise caused by a reduced intravascular volume. Manifestations include dry mucous membranes, reduced skin turgor and, in severe cases, tachycardia and hypotension.
Laboratory testing
The majority of patients with acute gastroenteritis secondary to E coli do not undergo routine laboratory testing.
Often only patients with signs and symptoms of moderate to severe illness require testing.[35][36]
Bacterial cultures of the stool and serotyping for O157:H7
Bacterial cultures of the stool should be sent from patients with gastroenteritis-like symptoms that are persistent, or are deemed moderate to severe by clinical criteria. Criteria include fever, dehydration, or presence of underlying illnesses. Stool cultures are regarded as mandatory in cases of bloody diarrhoea or signs of systemic toxicity.
Culture results are typically available after 2-4 days. Stool sample should be sent within the first 3 days of admission to hospital. Beyond this time, the yield is significantly reduced. Routine bacterial stool culture generally includes culture for Salmonella, Shigella, Campylobacter, and Shiga-like toxin-producing E coli. Stool is often tested for Clostridium difficile toxin as well under the appropriate clinical conditions.
Routine stool cultures will always be positive for E coli, which grows easily on standard plates and is a normal human gut microflora. In order to identify pathogenic species, such as E coli O157:H7, stool should be cultured on special plates such as sorbitol MacConkey agar. Stool specimens are simultaneously cultured for O157:H7 EHEC and assayed for non-O157:H7 EHEC.[37]
The presence of EHEC can be confirmed by performing serological testing to identify Shiga-like toxins using typing anti-serum, enzyme-linked immunosorbent assay (ELISA), immunofluorescence, immunochemistry, or latex agglutination. Alternatively, PCR can identify the genes encoding these toxins.
Identification of the specific strain is vital as it allows public health authorities to confirm, investigate, and control EHEC outbreaks.
Blood tests
Patients presenting in the community will not routinely have blood tests performed. In those presenting to the hospital setting, full blood count and renal function tests, including electrolytes, should be performed at minimum. Haemoglobin, platelet count, and renal function should be monitored for evidence of haemolytic uraemic syndrome, which is associated with E coli O157:H7 infection.
Blood cultures are only required if systemic illness is suspected (i.e., tachycardia, hypotension, fever), to exclude bacteraemia.
Inflammatory markers, such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), can be used for monitoring the patient's inflammatory response and as an objective sign of improvement, although there is no evidence for the usefulness of this strategy.
Imaging
Abdominal radiographs can be considered in any patient presenting with signs of severe toxicity (i.e., tachycardia, hypotension, fever ≥38°C [≥100.5°F]). Although non-diagnostic, radiographs can help to assess colonic inflammation and to exclude toxic dilatation or abdominal perforation.
In severely ill patients, abdominal computed tomography may be performed to exclude more serious causes of sepsis and diarrhoea (e.g., diverticular abscess, intestinal perforation).
Endoscopy
Endoscopy often reveals colonic inflammation, but is non-diagnostic. In patients with negative cultures, or persistent diarrhoea despite conservative management, a gastroenterology consult for possible colonoscopy is recommended to exclude other causes of diarrhoea (e.g., inflammatory bowel disease, pseudomembranous colitis). Sigmoidoscopy is often sufficient to visualise the mucosa and obtain tissue biopsies.
Colonoscopy is generally avoided in moderate to severe colitis due to the increased risk of perforation. The decision to perform a colonoscopy should be made by a gastroenterologist.
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