Poliomyelitis (polio) is caused by an enterovirus, poliovirus. Infection involves the gastrointestinal tract, and may progress to the central nervous system, resulting in paralysis. Acute flaccid paralysis (AFP) occurs in less than 1% of infections. More than 90% of infections are asymptomatic or are associated with a non-specific fever. About 10% are associated with a minor illness characterised by fever, headache, malaise, nausea and vomiting. Paralysis is usually asymmetric, the maximum extent of which is usually reached within 3–4 days of disease onset. Any paralysis still present after 60 days is likely to be permanent.1 Although wild poliovirus transmission has ceased in the majority of countries in the world, the threat of importation to Australia continues.
Vaccine-associated paralytic poliomyelitis (VAPP) is acute flaccid paralysis due to a Sabin-like poliovirus (i.e. a virus similar to that used in the Sabin live attenuated oral poliovirus vaccine [OPV]). A vaccine-derived poliovirus (VDPV) is defined as having 1%–15% nucleic acid sequence variation from the prototype Sabin strain. The variation is due to long-term (>1 year) virus replication after administration of OPV. The virus replication may occur in an individual with an immunodeficiency (iVDPV) or through sustained person-to-person transmission in areas with low OPV coverage (circulating or cVDPV). VDPVs not clearly assigned to either of these categories are known as ambiguous VDPVs (aVDPV).2
See Appendix 6.6 for pre-2004 definition
National definition from January 2004:3
Both confirmed and probable cases are notifiable. Confirmed cases require laboratory definitive evidence and clinical evidence. Probable cases are also notifiable, and require clinical evidence and that the case not be discarded as non-polio acute flaccid paralysis by the Polio Expert Committee.
Hospitalisations and deaths
The ICD-10-AM/ICD-10 code A80 (acute poliomyelitis) was used to identify hospitalisations and deaths.
Note: This code includes VAPP and specific codes for indigenous and imported wild-type poliovirus infection. ‘Sequelae of poliomyelitis’ (ICD-10 code B91) were not included in these analyses.
Notifications, hospitalisations and deaths
There was 1 confirmed notification of acute polio in a 22-year old male student from Pakistan in July 2007, who acquired wild-type poliovirus (type 1) infection while visiting his family in Pakistan.4–6 He was hospitalised upon his return to Melbourne but, as his hospital separation date was after the end of June 2007, he is not included in the present analysis of hospitalisation data. From July 2005 to June 2007, there were 8 hospitalisations with a recorded diagnosis of acute poliomyelitis. Of these, 6 were coded as acute unspecified poliomyelitis (A80.9), 1 as acute paralytic poliomyelitis (other and unspecified) (A80.3) and 1 as acute non-paralytic poliomyelitis (A80.4). This latter hospitalisation was of a young male who was the only case where poliomyelitis was coded as the principal diagnosis. Six of the 8 separations recorded as acute poliomyelitis were among persons aged ≥50 years. No hospitalisations were recorded in those aged <15 years. There were no deaths coded as due to poliomyelitis in 2005 or 2006.
Although Australia and the Western Pacific Region were declared polio-free in October 2000,7 the imported case of polio notified in 2007 is a reminder that, unless global polio eradication is achieved, ongoing vigilance in polio surveillance and maintenance of high levels of vaccination coverage are critical in maintaining successes in polio control achieved to date. As there have been no reports of indigenous wild-type poliovirus transmission in Australia for at least 30 years, the hospitalised cases reported here are almost certainly not missed notifications of acute infection due to indigenous wild-type poliovirus. Some hospitalisations could represent cases of AFP where polio could not be excluded, but most are likely to be adults with late effects of polio rather than acute cases, as indicated by the age distribution of the hospitalisations. However, imported cases of polio can include persons of any age, as exemplified by the 2007 importation event involving a young adult who had been fully immunised as a child.6 The current hospitalisation data suggest an ongoing improvement in coding practices compared to earlier periods where there were many more hospitalisations in older age groups miscoded as acute poliomyelitis.
Although Australia has been declared polio-free, achieving high quality AFP surveillance remains an important challenge. Such surveillance is required to detect any imported cases of wild-type poliovirus infection, cases of VAPP, and outbreaks of circulating vaccine-derived polioviruses. In Australia, surveillance of AFP in children <15 years of age is coordinated through the Victorian Infectious Diseases Reference Laboratory in collaboration with the Australian Paediatric Surveillance Unit. AFP cases are notified and stool specimens are referred to the Australian National Poliovirus Reference Laboratory for testing for polioviruses and other enteroviruses. Cases are referred to the Polio Expert Committee for a determination as to the cause of the AFP. In 2006, 48 eligible cases were received and 43 of these had sufficient information available for review and were classified as non-polio AFP.8 In 2007, there were 27 eligible cases and 26 were classified as non-polio AFP. The remaining case could not be discarded as non-polio AFP based on the available information and was reported to WHO as polio-compatible.9 The onset date of this case was not consistent with the case of hospitalisation for which the principal diagnosis was classified as acute non-paralytic poliomyelitis.
The WHO target for surveillance of AFP in a polio-free country (1 notified case of non-polio AFP per 100,000 children aged <15 years) has only been intermittently achieved in Australia (in 2000, 2001, 2004 and 2006). The rates in 2006 and 2007 were 1.1 and 0.65 per 100,000, respectively.8,9 The WHO target of faecal sampling from 80% of AFP cases has never been achieved, with the 52% sampling proportion achieved in 2007 the highest to date (previously 19%–36%, with a proportion of 21% in 2006).8–11
The global aim to eradicate polio by 2000 has proven elusive, prompting ongoing discussion and debate about the feasibility and desirability of elimination.12,13 In 2006 and 2007, endemic transmission of wild-type poliovirus remained constrained to four countries (Afghanistan, India, Nigeria and Pakistan) and the strategies used to control outbreaks following importations in 2005 seemed successful, with a dramatic fall in these cases. There were 1,997 and 1,315 wild poliovirus cases reported to WHO in 2006 and 2007, respectively.14 A total of 12 countries reported cases caused by wild poliovirus in 2007. The Global Polio Eradication Initiative Strategic Plan 2009–2013 will have five main objectives (interrupt wild poliovirus transmission; ensure sustainable surveillance for polioviruses; achieve certification and containment of wild polioviruses; prepare for VAPP and VDPV elimination and the post-OPV era; plan for restructuring of the Global Polio Eradication Initiative for the VAPP/VDPV Elimination Phase).15 Updates on the global polio situation are available at the Global Polio Eradication Initiative website (www.polioeradication.org).
In November 2005, inactivated poliovirus vaccine (IPV) became a funded part of the routine childhood immunisation schedule in Australia, with doses given at 2, 4 and 6 months and 4 years of age. With the replacement of OPV with IPV in Australia, incidental detection of polioviruses in faecal specimens should no longer occur, with the last routine isolation of Sabin-like polioviruses from submitted specimens occurring in 2006.8 Future poliovirus isolations will, therefore, require full investigation.11 An important goal in the diagnosis of all AFP cases is the exclusion of an imported wild or vaccine-associated poliovirus as the cause. The likelihood of local transmission following importation will be dependent upon the vaccination coverage locally and living conditions, primarily relating to the likelihood of faecal contamination of the water supply. Such contamination remains a possibility in rural and remote areas of Australia.16 Travellers should be reminded to ensure that they are vaccinated against polio.17
In 2008, the Australian Government Department of Health and Ageing released An acute flaccid paralysis and poliomyelitis response plan for Australia.18 The plan outlines the routine surveillance procedures for AFP cases in Australia, focusing on children <15 years of age. The plan also acts as a guide for the investigation of and response to a case of polio in a person of any age.
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2. Centers for Disease Control and Prevention. Update on vaccine-derived polioviruses. MMWR Morb Mortal Wkly Rep 2006;55(40):1093–1097.
3. Communicable Diseases Network Australia. Surveillance case definitions for the Australian National Notifiable Diseases Surveillance System. 2004. Available from: http://www.health.gov.au/internet/main/publishing.nsf/Content/cdna-casedefinitions.htm Accessed on 24 August 2009.
4. Thorley B, Kelly H, Roberts J. Importation of wild poliovirus into Australia, July 2007. Commun Dis Intell 2007;31(3):299.
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12. Chumakov K, Ehrenfeld E, Wimmer E, Agol VI. Vaccination against polio should not be stopped. Nat Rev Microbiol 2007;5(12):952–958.
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14. World Health Organization. Polio case count. Geneva, World Health Organization, 2009. Available from: http://www.who.int/vaccines/immunization_monitoring/en/diseases/poliomyelitis/case_count.cfm Accessed on 1 February 2009.
15. Global polio eradication initiative. Strategic plan 2009–2013. Framework document. December 2008. Available from: http://www.polioeradication.org/content/publications/PolioStrategicPlan09-13_Framework.pdf Accessed on 1 February 2009.
16. Durrheim DN, Massey P, Kelly H. Re-emerging poliomyelitis – is Australia’s surveillance adequate? Commun Dis Intell 2006;30(3):275–277.
17. Thorley BR, Brussen KA, Elliott EJ, Kelly HA. Vigilance is required for Australia to remain polio free. Med J Aust 2006;184(9):474–475.
18. Office of Health Protection, Department of Health and Ageing. An acute flaccid paralysis and poliomyelitis response plan for Australia. Canberra: Australian Government Department of Health and Ageing, 2008. Available from: http://www.health.gov.au/internet/main/publishing.nsf/Content/polio-plan.htm Accessed on 29 July 2009.