Food poisoning is usually a mild illness that may resolve on its own after a bout of stomach upset. However, in some cases it might be more serious needing therapy.
Symptoms of food poisoning like abdominal cramps, nausea and vomiting, diarrhea and weakness and association with a recent intake of contaminated food or water is often diagnostic of the condition.
However, sometimes blood tests, tests for the infected stools or even a sigmoidoscopy and other imaging tests may be prescribed to find out the causative organism. (1)
There are several steps for the diagnosis of food poisoning. (1-5)
History of intake of contaminated food
In most cases, the patient volunteers such information.
History of recent return from travel to a developing or underdeveloped country and drinking contaminated water or eating contaminated food should also be mentioned.
A complete physical examination may be needed especially to rule out signs of dehydration.
Dehydration is usually caused due to excessive fluid loss due to diarrhea or vomiting.
Dehydration is characterized by dry skin that remains tented after a pinch, sunken eyes, dry mouth, no sweating in the groins or armpits, no urination for long durations etc.
Weakness or paralysis may also be diagnosed on physical examination and may be indicative of Botulism which needs immediate therapy.
Blood pressure, pulse and temperature are also measured. Severe dehydration is manifested with weak pulse and low blood pressure.
If there is accompanying fever, temperature assessment may be helpful.
Routine blood tests
Routine blood tests may be ordered in some patients with severe food poisoning.
Sometimes these are ordered to check for levels of blood electrolytes and to check for adequate kidney functions.
In case of suspected hepatitis A liver function tests may also be ordered.
Stool samples are examined in case of Salmonella, Shigella and Campylobacter. These infections commonly lead to bloody diarrhea.
If there is a suspected parasitic infestation the stool samples are examined and the parasite is identified under the microscope.
Sometimes stool culture may be prescribed. The sample is allowed to stand in the laboratory in ideal environmental conditions and growth of the microorganism is checked.
Rectal examination may be needed especially in case of bloody stools.
The doctor inserts a lubricated and gloved finger gently into the rectum for this tests and assess if there are breaks in the rectal wall.
If the symptoms are suspected to be caused by any other illness, imaging studies are recommended.
These include CT scan of the abdomen.
Sometimes a sigmoidoscopy may be recommended. This involves insertion of a thin long tube within the rectum up to the colon. The tube has a camera on the tip. This helps diagnose any pathology within the intestinal walls.
In pregnant women with symptoms there may be a risk of Toxoplasma infection. For this a toxoplasmosis test is advised.
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