Polio is a disease caused by infection with the poliovirus. The virus spreads by:

• Direct person-to-person contact
• Contact with infected mucus or phlegm from the nose or mouth
• Contact with infected feces

The virus enters through the mouth and nose, multiplies in the throat and intestinal tract, and then is absorbed and spread through the blood and lymph system. The time from being infected with the virus to developing symptoms of disease (incubation) ranges from 5 to 35 days (average 7 to 14 days). Most people do not develop symptoms.

Risks include:

• Lack of immunization against polio
• Travel to an area that has had a polio outbreak

As a result of a global vaccination campaign over the past 25 years, polio has largely been eliminated. The disease still exists in some countries in Africa and Asia, with outbreaks occurring in groups of people who have not been vaccinated. For an updated list of these countries, visit the website: www.polioeradication.org.

There are 3 basic patterns of polio infection: subclinical infections, nonparalytic, and paralytic. Most people have subclinical infection, or may not have any symptoms.

SUBCLINICAL INFECTION SYMPTOMS

• General discomfort or uneasiness (malaise)
• Headache
• Red throat
• Slight fever
• Sore throat
• Vomiting

People with subclinical polio infection might not have symptoms, or mild symptoms may last 72 hours or less.

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.

During a physical examination, the health care provider may find:

• Abnormal reflexes
• Back stiffness
• Difficulty lifting the head or legs when lying flat on the back
• Stiff neck
• Trouble bending the neck

Tests that may be done include:

• Cultures of throat washings, stools, or spinal fluid
• Spinal tap and examination of the spinal fluid (CSF examination) using polymerase chain reaction (PCR)
• Test for levels of antibodies to the polio virus

The goal of treatment is to control symptoms while the infection runs its course. There is no specific treatment for this viral infection.

People with severe cases may need lifesaving measures, especially help with breathing.

Symptoms are treated based on how severe they are. Treatment may include:

• Antibiotics for urinary tract infections
• Moist heat (heating pads, warm towels) to reduce muscle pain and spasms
• Painkillers to reduce headache, muscle pain, and spasms (narcotics are not usually given because they increase the risk of breathing trouble)
• Physical therapy, braces or corrective shoes, or orthopedic surgery to help recover muscle strength and function

The outlook depends on the form of the disease (subclinical, or paralytic) and the body area affected. Most of the time, complete recovery is likely if the spinal cord and brain are not involved.

Brain or spinal cord involvement is a medical emergency that may result in paralysis or death (usually from respiratory problems).

Disability is more common than death. Infection that is located high in the spinal cord or in the brain increases the risk of breathing problems.

Health problems that may result from polio include:

• Aspiration pneumonia
• Cor pulmonale (a form of heart failure found on the right side of the circulation system)
• Lack of movement
• Lung problems
• Myocarditis
• Paralytic ileus (loss of intestinal function)
• Permanent muscle paralysis, disability, deformity
• Pulmonary edema
• Shock
• Urinary tract infections

Post-polio syndrome is a complication that develops in some people, usually 30 or more years after they are first infected. Muscles that were already weak may get weaker. Weakness may also develop in muscles that were not affected before.

Call your provider if:

• Someone close to you has developed poliomyelitis and you haven't been vaccinated.
• You develop symptoms of poliomyelitis.
• Your child's polio immunization (vaccine) is not up to date.

Polio immunization (vaccine) effectively prevents poliomyelitis in most people (immunization is over 90% effective).

Poliomyelitis; Infantile paralysis; Post-polio syndrome

Romero JR, Modlin JF. Poliovirus. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 173.

Silver JK. Post-poliomyelitis syndrome. In: Frontera WR, Silver JK, Rizzo Jr TD, eds. Essentials of Physical Medicine and Rehabilitation. 2nd ed. Philadelphia, PA: Elsevier Saunders; 2008:chap 137.

Simoes EAF. Polioviruses. In: Kliegman RM, Stanton BF, St Geme JW III, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 249.

Updated by: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.