The evaluation of St. Louis encephalitis begins with a history and physical examination.

Physical findings in someone with St. Louis encephalitis may include:

• Rash
• Lymph node swelling
• Fever
• Brudzinski sign:
• Bending of the neck causes the hips and knees to bend
• Kernig sign:
• Extending the knees with the hips flexed causes pain and muscle spasms
• Papilledema:
• Increased pressure in the eyes
• Lethargy:
• Excessive sleepiness
• Confusion

Tests are necessary to make the diagnosis of St. Louis encephalitis.

Tests that may be used to evaluate St. Louis encephalitis include:

• Spinal tap
• This is the most important test to diagnose meningitis or encephalitis
• Encephalitis or meningitis may cause the spinal fluid to become cloudy
• Blood cultures
• Complete blood count
• Blood serology:
• Blood test that identifies the virus.

Less commonly used tests that may be used to evaluate St. Louis encephalitis include:

• CT scan of the brain
• MRI scan of the brain