Investigations
1st investigations to order
stool cultures
Test
Bacterial cultures of the stool should be sent from patients with gastroenteritis-like symptoms that are persistent or have been deemed moderate to severe by clinical criteria. Criteria include such as fever, dehydration, or presence of underlying illnesses. Stool pathogen panels are used in many institutions.
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. Diarrhoeal stool sample should be sent within the first 3 days of admission to hospital. Beyond this the yield is significantly reduced.
Routine stool cultures will always be positive for Escherichia coli, which grows easily on standard plates and is part of normal human gut microflora. To identify pathogenic species such as E coli O157:H7, stool should be cultured on special plates such as sorbitol MacConkey agar.
Result
positive for pathogenic E coli species such as E coli O157:H7
FBC
Test
Should be performed in hospitalised patients with evidence of more severe, systemic presentations.
Escherichia coli O157:H7 is associated with haemolytic uraemic syndrome, which may manifest with anaemia and thrombocytopenia. Anaemia may also be caused by gastrointestinal blood loss.
Result
elevated leukocyte count, sometimes low haemoglobin and/or platelets
renal function and electrolytes
Test
Should be performed in hospitalised patients with evidence of more severe, systemic presentations.
Impaired renal function may be related to volume depletion or to haemolytic uraemic syndrome.
Result
raised urea and creatinine, hypokalaemia
Investigations to consider
identification of Shiga toxin-producing E coli infection
Test
The presence of enterohaemorrhagic E coli (EHEC) can be confirmed by performing serological testing to identify Shiga-like toxins using typing antiserum, enzyme-linked immunosorbent assay (ELISA), immunofluorescence, immunochemistry, or latex agglutination. Alternatively, PCR can identify the genes encoding these toxins.
Identification of specific strains is vital as it allows public health authorities to confirm, investigate, and control EHEC outbreaks.
Result
identification of EHEC strain
blood cultures
Test
Perform if systemic symptoms (i.e., tachycardia, hypotension, fever) are present.
Result
positive in the setting of Escherichia coli bacteraemia
inflammatory markers (CRP and/or erythrocyte sedimentation rate)
Test
May be useful for monitoring progression; levels fall with patient recovery from illness.
Result
elevated
abdominal x-ray
Test
Consider if signs of severe toxicity (i.e., tachycardia, hypotension, fever ≥38°C [≥100.5°F]) are present.
While non-diagnostic, radiographs can help to assess colonic inflammation and to exclude toxic dilatation or intestinal perforation.
Serial x-rays can help determine improvement or deterioration.
Result
loss of haustrations, bowel wall thickening, thumb-print sign, free air
endoscopy
Test
Endoscopic evaluation is not required in the vast majority of patients with gastroenteritis.
In patients with negative cultures or persistent diarrhoea and despite conservative management, sigmoidoscopy should be performed to exclude other causes of diarrhoea.
Colonoscopy is rarely required, and is usually postponed until colonic inflammation has resolved (due to the increased risk of perforation).
Result
erythematous, friable mucosa, mucopurulent exudate, frank ulceration; changes specific to alternative diagnosis
abdominal CT scan
Test
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).
Result
mural thickening of the colon, dilatation, and ileus may be seen
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