Poliomyelitis

Notification requirements for poliomyelitis

Poliomyelitis is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone upon initial diagnosis (presumptive or confirmed). Pathology services must follow up with written notification within 5 days.

This is a Victorian statutory requirement.

Primary school and children’s services centres exclusion for poliomyelitis

Exclude for at least 14 days from onset; readmit after receiving medical certificate of recovery. Contacts are not excluded.

Infectious agent of poliomyelitis

Poliovirus is an enterovirus and a member of the Picornaviridae family; types 1, 2 and 3 cause disease, although type 2 has been eradicated as a wild-type virus. Type 3 virus has not been detected anywhere since November 2012; therefore, type 1 virus now appears to be the only circulating wild virus globally.

Identification of poliomyelitis

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 per cent 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, and the maximum extent of paralysis is usually reached within 3–4 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 can occur and is life threatening. After 60 days, the existing degree of paralysis is likely to be permanent.

Sensory loss is very rare, and its occurrence should strongly suggest some other diagnosis, such as Guillain-Barré 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, rather than to persistent or reactivated poliovirus infection.

Vaccine-associated paralytic poliomyelitis (VAPP) is a very rare complication in recipients of oral polio vaccine (which has attained neurovirulence) or in their contacts. Approximately one case occurs 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 for children. Circulating vaccine-derived polioviruses (cVDPVs) can also occur. The oral vaccine strain regains neurovirulence through person-to-person transmission; this has caused outbreaks in regions where oral polio vaccine is still in use.

Diagnosis

A clinical history, including the vaccination status of the 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 the 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 of poliovirus

The incubation period is between 3 and 35 days; for paralytic cases, it is 7–14 days.

Public health significance and occurrence of poliomyelitis

Before 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 dropped from an estimated 350,000 in 125 countries in 1988 to just 480 reported cases in only 10 polio-endemic countries in 2001.

By early 2012, three countries had still not interrupted endemic transmission of polio: Pakistan, Afghanistan and Nigeria. Chad and the Democratic Republic of the Congo have re-established transmission. Niger, the Central African Republic, China and Cameroon have active outbreaks.

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, a less pronounced increase can occur as a seasonal peak in the rainy season.

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

Polio remains a predominantly childhood illness; 80 per cent to 90 per cent of cases occur in children less than 5 years old, although outbreaks affecting young adults have occurred.

Reservoir for poliovirus

Humans.

Mode of transmission of poliovirus

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 6 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 handwashing for parents following nappy changing and disposal is important.

Period of communicability of poliomyelitis

The risk of transmission of infection is greatest for the 7–10 days before and following the onset of symptoms.

The virus persists in the pharynx for approximately 1 week and in the faeces for up to 6 weeks, or longer (potentially years) in the immunosuppressed.

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

Susceptibility and resistance to poliomyelitis

All non-immune people are susceptible to infection.

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

The vaccine efficacy of OPV and inactivated polio vaccine (IPV) after a primary course is 95 per cent and thought to be lifelong. IPV gives protection against all three types of poliovirus. OPV has different formulations depending on context. For routine immunisation, the trivalent formulation (tOPV), which covers all three types, is used. Supplementary immunisation activities, including subnational immunisation rounds, can also employ a monvalent vaccine (mOPV) for type 1 or bivalent vaccine (bOPV) for types 1 and 3, depending on circulating types and immunity levels.

Infants born of immune mothers have transient passive immunity.

Control measures for poliomyelitis

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 healthcare workers in possible contact with polio cases.

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

The National Immunisation Program polio immunisation consists of a primary course of IPV given at 2, 4 and 6 months of age, with a booster at 4 years of age. It is also given to school-aged children and refugees (aged 8 years and older) who are unimmunised or incompletely immunised.

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) and cVDPV, many industrialised countries have now changed to IPV alone for routine immunisations.

OPV is still recommended in many 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. Polio eradication will ultimately require the synchronised cessation of OPV in order to prevent vaccine-derived cases. The cessation of type 2 polio in existing oral vaccines is currently under consideration, since wild type 2 polio was eradicated in 1998 and cases from type 2 are now caused only by vaccine-derived viruses.

Control of case

There is no specific treatment for poliovirus. Symptomatic 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. 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.

For all cases, isolate in hospital or at home and use standard precautions. Isolation should continue until two stool samples taken 7 days apart are shown to be negative for poliovirus. Children must be excluded from primary schools and children’s services centres for at least 14 days from onset. They may return only after receiving a medical certificate of recovery.

Control of contacts

Vaccination of families and other close contacts is recommended but may not contribute to immediate control because susceptible contacts are often infected by the time the first case is recognised. Household contacts require home quarantine until two negative stool specimens taken 24–48 hours apart have been collected.

Active case finding, especially among children, ensures the 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.

Proper cleaning and disinfection of areas contacted by an infected individual are required to prevent onward transmission. This must occur in toilets that the case has used while infectious, which may include toilets in the case’s home, doctor’s surgery, airplanes and airports. Effective disinfectants are those that contain free chlorine.

Reinforce good personal hygiene practices and suggest a clean-up of kitchen and bathroom surfaces and fixtures used by the case during their infectious period, using a chlorine-based solution, to prevent the spread of viruses to others. Cases should refrain from preparing food for others while symptomatic.

Outbreak measures for poliomyelitis

In countries such as Australia where polio has been eradicated, a single case of polio is considered a public health emergency. The department must be notified immediately. At the national level, the Poliomyelitis Outbreak Response Plan for Australia would be activated.

The department investigates to:

• determine whether the patient’s disease is caused by an imported wild virus, an imported vaccine-derived poliovirus or a poliovirus acquired from a laboratory
• determine whether the patient’s disease is a VAPP case and, if it is 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.