Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures

Victorian statutory requirement

Poliomyelitis (Group A disease) must be notified immediately by telephone or fax followed by written notification within five days.

School exclusion: applicable for at least 14 days from onset. Re-admit after receiving medical certificate of recovery.

Infectious agent

Poliovirus is an enterovirus; types 1, 2 and 3 cause disease.

Identification

Clinical features
The majority of polio infections are either inapparent or present as a non-specific febrile illness. Flaccid paralysis occurs in less than 1% of poliovirus infections.

Symptoms of minor illness include fever, malaise, headache, nausea and vomiting. If the disease progresses to major illness, severe muscle pain and stiffness of the neck and back with flaccid paralysis may occur.

The most characteristic feature of polio paralysis is its asymmetric distribution, which affects some muscle groups while sparing others. Fever and muscle pain are generally present at onset with the maximum extent of paralysis usually reached within three to four days.

Progression of paralysis almost invariably halts when the patient becomes afebrile. The site of paralysis depends upon the location of nerve cell destruction in the spinal cord or brain stem. Proximal muscles of the extremities tend to be more involved than distal. The legs are more often affected than the arms. Paralysis of the respiratory and swallowing muscles is life threatening.

After 60 days the degree of existing paralysis is likely to be permanent. Sensory loss is very rare and its occurrence should strongly suggest some other diagnosis such as Guillain-Barr? syndrome.

Post-polio syndrome is an infrequent recurrence of muscle weakness that may occur many years after initial infection. It is thought to be due to progressive dysfunction and loss of motor neurons that compensated for the neurons lost during the original infection, not to persistent or reactivated poliovirus infection.

Vaccine-associated paralytic poliomyelitis (VAPP) is a very rare complication in recipients of oral polio vaccine or their contacts, with approximately one case per 2.4 million doses of vaccine. The risk is greater for the first dose than subsequent doses and is slightly greater for adults than children.

Method of diagnosis
A clinical history including vaccination status of case and household contacts and any recent travel is important.

Diagnosis is made by isolation of virus from cerebrospinal fluid (CSF), faecal specimens or oropharyngeal secretions. Two separate faecal specimens taken at least 24 hours apart and within 14 days of onset of symptoms give the best chance of diagnosis. CSF usually reveals a mild elevation in protein and a lymphocytosis.

The Department requires that all suspected cases of polio have appropriate faecal specimens sent for analysis by the National Poliovirus Reference Laboratory (NPRL), managed by the Victorian Infectious Diseases Reference Laboratory. The NPRL can also differentiate between ‘wild-type’ and vaccine-associated strains.

The Department coordinates with clinicians and the NPRL to ensure that appropriate infection control procedures are followed in the collection, transfer and analysis of all clinical specimens from patients with suspected polio.

Incubation period

The range is between three to 35 days with seven to 14 days for paralytic cases.

Public health significance & occurrence

Prior to vaccination programs polio occurred worldwide. Since the Global Polio Eradication Initiative was launched in 1988, three WHO regions have been certified polio-free: the Americas in 1994, the Western Pacific (of which Australia is a member) in 2000, and Europe in 2002. Polio cases have dropped from an estimated 350 000 in 125 countries in 1988 to just 480 reported cases in only ten polio-endemic countries in 2001.

By 2003, six countries were still reporting new polio cases: India, Niger, Pakistan, Afghanistan, Egypt, and Nigeria.

In endemic areas, cases of polio occur both sporadically and in epidemics. In temperate climates an increase in cases occurs during the late summer and autumn, in tropical countries an increase is less pronounced but can occur as a seasonal peak in the rainy season.

In countries where polio has been eradicated, importation from non-vaccinated individuals remains a threat.

Polio remains a predominantly childhood illness with 80% to 90% of cases occurring in children less than five years old.

Reservoir

Humans.

Mode of transmission

Wild poliovirus is spread through faeces and saliva. It is primarily transmitted through faecal-oral spread and is an important consideration where sanitation is poor.

‘Live’ oral polio vaccine (OPV) virus can be shed in the faeces for six weeks and may lead to infection in unvaccinated contacts. Unvaccinated household contacts of a case should be vaccinated at the same time. Stressing the importance of hand washing for parents following nappy changing and disposal is important.

Period of communicability

The risk of transmission of infection is greatest for the seven to ten days prior to and following the onset of symptoms.

The virus persists in the pharynx for approximately one week and in the faeces for up to six weeks, or longer in the immunosuppressed.

Transmission of the virus is possible for as long as the virus is excreted.

Susceptibility & resistance

All non-immune people are susceptible to infection.

After infection from both clinically recognisable and inapparent infections, type specific lifelong immunity occurs. Reinfection is rare but can occur if infected with poliovirus of a different type.

Vaccine efficacy of OPV and Inactivated Polio Vaccine (IPV) after a primary course is 95% and thought to be life long. Both vaccines give protection against all three types of poliovirus.

Infants born of immune mothers have transient passive immunity.

Control measures

Preventive measures
Universal vaccination in early childhood is the most effective means of preventing and eradicating poliomyelitis. Catch-up immunisation is also recommended for unimmunised or partially immunised adults at risk of exposure such as those travelling overseas and health care workers in possible contact with polio cases.

Immunisation can be given as an intramuscular IPV, or as a live OPV.

Under the National Immunisation Program, polio immunisation consists of a primary course of OPV given as two drops by mouth at 2, 4 and 6 months of age with a booster at four years of age. IPV is given for individuals with immunosuppression from disease or chemotherapy and for their siblings and household contacts.

Both IPV and OPV give mucosal and humoral protection, however IPV produces considerably lower levels of intestinal immunity than OPV.

Due to the successful elimination of polio in some regions and the concern with OPV of Vaccine Associated Paralytic Poliomyelitis (VAPP), many industrialised countries have now changed to IPV alone for routine immunisations. IPV is the vaccine recommended on the ASVS subject to the availability of further combination vaccines. The Australian Government is currently reviewing this funding decision.

OPV is still recommended in developing countries because of the higher risk of exposure to wild poliovirus, the low cost of the vaccine, the ease of its administration and its excellent capacity to provide population-level immunity.

Control of case
There is no specific treatment against poliovirus. Cases require expert supervision and may need ventilation support. Early physiotherapy may increase the level of function and reduce the risk of physical deformities as a result of paralytic polio.

Enteric precautions should be initiated in hospital settings. These are often of little benefit in household settings as susceptible contacts are likely to have been exposed prior to diagnosis.

In communities with appropriate modern sewerage systems, faeces and urine from infected patients can be disposed of directly into sewers without preliminary disinfection. Terminal disinfection is required for all other potentially contaminated items.

Control of contacts
Vaccination of families and other close contacts is recommended but may not contribute to immediate control due to susceptible contacts often being infected by the time the first case is recognised.

Active case finding, especially among children, ensures early detection of related cases and facilitates control.

Control of environment
In communities with modern sewerage systems, faeces and urine can be disposed of directly into the system without preliminary disinfection.

Cases and carers should be advised about the importance of strict hand washing, covering the mouth when coughing, sneezing into disposable tissues, and the appropriate cleaning or disposal of contaminated objects.

Outbreak measures

In countries such as Australia where polio has been eradicated a single case of polio is considered a public health emergency and the Department of Human Services must be notified immediately. The Department investigates to:

• determine whether the patient’s disease represents an indigenous, imported or VAPP case
• if believed to be a VAPP case, obtain details of vaccine history, batch number, virus type, severity and persistence of residual paralysis 60 days after onset
• supervise all appropriate case and contact control measures, as outlined above.