There are three basic patterns of polio infection: subclinical infections, nonparalytic, and paralytic. Approximately 95% of these are subclinical infections, which may go unnoticed.

Clinical poliomyelitis affects the central nervous system (brain and spinal cord) and is divided into nonparalytic and paralytic forms. It may occur after recovery from a subclinical infection.

SUBCLINICAL INFECTION

• no symptoms, or symptoms lasting 72 hours or less
• slight fever
• headache
• general discomfort or uneasiness (malaise)
• sore throat
• red throat
• vomiting

NONPARALYTIC POLIOMYELITIS

• symptoms last 1 to 2 weeks
• moderate fever
• headache
• vomiting
• diarrhea
• excessive tiredness, fatigue
• irritability
• pain or stiffness of the back, arms, legs, abdomen
• muscle tenderness and spasm in any area of the body
• neck pain and stiffness
• pain front part of neck
• back pain or backache
• leg pain (calf muscles)
• skin rash or lesion with pain
• muscle stiffness

PARALYTIC POLIOMYELITIS

• fever, occurring 5 to 7 days before other symptoms
• headache
• stiff neck and back
• muscle weakness, asymmetrical (only on one side or worse on one side)
  • rapid onset
  • progresses to paralysis
  • location depends on where the spinal cord is affected
• abnormal sensations (but not loss of sensation) of an area
• sensitivity to touch, mild touch may be painful
• difficulty beginning to urinate
• constipation
• bloated feeling of abdomen
• swallowing difficulty
• muscle pain
• muscle contractions or muscle spasms, particularly in the calf, neck, or back
• drooling
• breathing difficulty
• irritability or poor temper control
• positive Babinski's reflex

Examination may shows signs of meningeal irritation (similar to meningitis), such as stiff neck or back stiffness with difficulty bending the neck. When sitting, the person may need to support the body with the arms.

The person may have difficulty lifting the head or lifting the legs from a supine position (lying flat on the back). Reflexes may be abnormal. The disorder may resemble encephalitis, and it may affect the cranial nerves and cause difficulty with facial expression, swallowing, chewing, and so on. It may also cause choking or difficulty breathing.

Viral cultures of throat washings, stools, or cerebrospinal fluid (CSF) confirm the diagnosis (see CSF collection). Routine CSF examination may be normal or show slight increase in pressure, protein, and white blood cells.