The evaluation of bacterial gastroenteritis begins with a medical history and physical examination.

Physical findings in those with bacterial gastroenteritis may include:

• Fever
• Signs of dehydration

Signs of dehydration include:

• Pale, dry skin
• Dry eyes
• Dry mouth
• Decreased urination
• Sunken eyes
• Sunken fontanelle in infants
• Rapid pulse
• Low blood pressure when standing
• Confusion
• Lethargy:
• A condition of excessive sleepiness or drowsiness.

Tests are required to confirm the diagnosis of bacterial gastroenteritis. A stool culture is performed on a stool specimen, in order to investigate suspected bacterial infection. Stool may also be tested for C. difficile toxin, which is used to diagnose pseudomembranous colitis. A stool examination for ova and parasites may be helpful to detect parasitic infections.

A stool culture can detect:

• Cholera
• Shigella infection
• Campylobacter enteritis
• Cryptosporidium enterocolitis
• Giardiasis
• Pseudomembranous colitis:
• Clostridium difficile
• Salmonella gastroenteritis
• Traveler's diarrhea due to bacterial infection
• E. coli

Tests that may be used to evaluate bacterial gastroenteritis include:

• Complete blood count
• Liver profile
• Kidney profile