Poliomyelitis

Overview

Poliomyelitis, commonly known as polio, is a highly contagious viral disease caused by poliovirus and predominantly affects young children under the age of 5.

Disease epidemiology

Humans are the only reservoir for poliovirus. Since the introduction of poliovirus vaccine, most countries have eradicated poliomyelitis. Currently, only 2 countries, namely Pakistan and Afghanistan, still have ongoing transmission of wild polioviruses.

Singapore was certified polio-free by the World Health Organization (WHO) in 2000, with the last indigenous case of poliomyelitis in Singapore being notified in 1973.

Pathogen(s)

Poliovirus types 1, 2 and 3.

Transmission

Polio primarily transmits via the faecal-oral route (i.e. through food, water or other objects that are contaminated with the stool of an infected person). Less commonly, it can transmit via infectious respiratory particles (IRPs) when an infected person coughs or sneezes.

Incubation period: Typically 7 to 14 days; ranging from 3 to 35 days.

Infectious period: From 7 to 10 days before till 1 to 2 weeks after symptoms onset (may be up to 6 weeks as the virus can continue to be excreted in the faeces of an infected person).

Clinical features

Poliovirus infection presents with a wide clinical spectrum, with the majority of cases being asymptomatic. About 25% will have a mild flu-like illness that is self-limiting. A small proportion of infected cases go on to develop more serious manifestations (including paralysis).

Depending on the part of the spinal cord or brainstem affected, 3 forms of paralytic polio have been seen:

1. Spinal paralytic polio: This is preceded by a “minor” illness with fever, muscle pain, headache, nausea, vomiting and stiff neck/back and less frequently, signs of aseptic meningitis. The minor illness lasts 1 to 3 days followed by a symptom free period of 1-5 days before the onset of “major” illness of paralysis. Paralysis which varies from single muscle involvement to quadriplegia, is usually asymmetric and typically flaccid with loss of tendon reflexes. There is no accompanying sensory loss.

2. Bulbar paralytic polio: Paralysis of the soft palate, pharynx and larynx resulting in dysphagia, nasal speech and dyspnea.

3. Polio encephalitis: Encephalitis is manifested by confusion and change in sensorium. This is an uncommon form of polio seen in infants. Seizures are common and there may be spastic paralysis as opposed to flaccid paralysis.

The most common differential diagnoses for an acute flaccid paralysis include transverse myelitis, Guillain–Barré syndrome and an infection by EV-71 or West Nile virus.

Risk factors

Risk factors include:

• Persons who are unvaccinated or partially vaccinated

• Persons who are exposed to the oral-faecal, respiratory or nasal secretions of the case or their contaminated environments

• Persons who have travel history to countries with ongoing or recent transmission of polio in the past 35 days

• Persons who have undergone stem cell transplantation and have not yet been re-vaccinated

Diagnosis

Detection of poliovirus in stool specimens through virus isolation; or when poliovirus is detected in cerebrospinal fluid analysis (CSF), stool, and respiratory samples, including throat swabs, through polymerase chain reaction (PCR), sequencing or virus isolation.

Treatment and management

There is no specific antiviral therapy. Management is supportive and symptomatic.

Precaution, prevention, and control

Isolation measures

All cases should be isolated, and droplet and contact precautions should be applied when attending to suspect or confirmed cases of polio.

Contact management

Close contacts will be contact traced by Ministry of Health and appropriately followed up (e.g., quarantine, phone surveillance or self-monitoring).

Vaccination

Vaccination is the most effective preventive measure for polio. Under the National Childhood Immunisation Schedule, children in Singapore receive inactivated polio vaccine (IPV) at 2, 4, and 6 months, and boosters at 18 months and 10 to 11 years.

For adults, vaccination is recommended for the following at-risk groups:

• Travellers to areas where polio is endemic or where recent transmission of polio has occurred. This should be decided in consultation with a travel medicine practitioner.

• Persons handling poliovirus isolates.

• Unvaccinated contacts of persons vaccinated with Oral Polio Vaccine (OPV).

Only a single dose is required for previously vaccinated adults. For unvaccinated adults, give 3 doses, with the second and third dose given after 1, 2, and 6 and 6–12 months after the first dose. If accelerated schedule is necessary, each dose should be spaced 4 weeks apart.

Notification

Poliomyelitis is a legally notifiable disease in Singapore.

Who should notify:

• Medical practitioners

• Laboratories

When to notify:

• On clinical suspicion or laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notification for more information.

Notification timeline:

• Immediately. No later than 24 hours.

Resources

Please refer to the Weekly Infectious Diseases Bulletin for the number of polio cases in Singapore.

For more information on polio, please refer to the WHO website.

For general travel advisory, please refer to Health Advice for Travellers.