Chapter reviewed and updated in December 2022. Added information about laboratory testing.
Chapter reviewed and updated in August 2017. A description of changes can be found at Updates to the Communicable Disease Control Manual.
New Zealand Epidemiology
Wild poliovirus has been eliminated from New Zealand with the last case of wild poliovirus occurring in New Zealand in 1977. No cases of vaccine-associated paralytic poliomyelitis (VAPP) have occurred in New Zealand since the introduction of inactivated polio vaccine (IPV) in 2002.
Internationally, and as of July 2017, states infected with wild poliovirus include Pakistan, Afghanistan and Nigeria. While there is an extremely low risk of cases being imported to New Zealand from these countries, all countries remain at risk of importing polio, especially those countries in the Lake Chad basin (including Cameroon, the Central African Republic, Chad and Niger). Unimmunised travellers who travel to infected states are at risk of infection.
On 5 May 2014 the Director-General of the World Health Organization declared the international spread of wild poliovirus a Public Health Emergency of International Concern (PHEIC) under the International Health Regulation, 2005.
More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website and from the New Zealand National Poliomyelitis Response Plan (updated 2014).
Poliomyelitis is caused by wild poliovirus types 1, or 3 or by live vaccine-derived poliovirus. Wild poliovirus type 2 was declared globally eradicated in 2015. Infection is established in the gastrointestinal tract. A minor illness (fever, malaise, headache, vomiting) occurs in about 10 percent of infections. Over 90 percent of infections are asymptomatic or involve non-specific fever. In a minority of cases (less than 1 percent), infection spreads to the central nervous system and is characterised by:
- having no other apparent cause
- acute flaccid paralysis (AFP) of one or more limbs with decreased or absent deep tendon reflexes in affected limbs
- no sensory or cognitive loss
- a possible effect on bulbar muscles.
In children who develop paralysis the illness may be biphasic, with the initial phase of a mild febrile illness of one to three days’ duration indistinguishable from that of many other viral infections. The child appears to recover, only to be struck down abruptly two to five days later with meningism, followed by paralysis. In adults and adolescents, the illness usually presents with a gradual onset of paralysis and muscular pain without the early symptoms.
Laboratory test for diagnosis
Laboratory confirmation requires isolation of poliovirus or detection of poliovirus nucleic acid from a clinical specimen. Different polioviruses will need to be tested for, depending on the type of polio suspected (for example, wild polioviruses or vaccine-derived strains).
Testing should be undertaken following notification of a suspected case of Acute Flaccid Paralysis (AFP) to the local Public Health Service (PHS), as well as reporting to the Paediatric Surveillance Unit (PSU) for cases of AFP in children.
Samples for Collection
The following clinical specimens can be collected for detecting the presence of polioviruses or related antibodies:
- Required: two fresh stool samples collected 24 hours apart within 14 days’ onset of the paralysis (or rectal swab with faecal material if stool is not immediately available). Samples can be collected up to the fourth week of illness for late presentation post-illness onset.
- a throat swab in universal transport medium (UTM) taken during the first week of illness.
- cerebral spinal fluid
Enterovirus PCR Testing
Enterovirus (EV) PCR testing should be undertaken as soon as possible, in the local laboratory where possible, with referral to ESR where this testing is not available locally.
For urgent suspected poliomyelitis samples, the turn-around time for an EV PCR result is typically 24-48 hours in regional labs depending on where the sample is referred from and to.
A negative enterovirus PCR is considered diagnostic for exclusion of Poliovirus. A pan-enterovirus positive result does not confirm Poliovirus and further testing will be required.
All positive PCR enterovirus samples should be sent to ESR’s Virology Laboratory in Wallaceville, which is the reference laboratory for genotyping and confirmation.
Isolation by culture and subsequent typing can take up to 28 days. Testing is primarily used for WHO confirmation and reporting as well as enhanced surveillance in New Zealand.
ITD RT-PCR (Intratypic Differentiation PCR) can be performed on enterovirus PCR positive samples in AFP cases to reduce the turnaround time and provide a further indicator of positivity, and rapid contact tracing prior to laboratory definitive evidence of Poliovirus infection from stool culture.
All EV PCR positive samples referred for typing and surveillance will undergo sequencing with a 1.5-week turnaround time.
Poliovirus serology testing does not differentiate between acquired or vaccine induced antibodies. Serology may assist in confirming a diagnosis of paralytic poliomyelitis.
Antibody tests for polio infection are available at ESR (minimum volume required is 300 uL serum). Both acute and convalescent sera should be referred together by the local testing laboratory.
Polio serology may be requested for:
- diagnosis of poliovirus infection when the diagnosis cannot be established by molecular or culture-based methods, by comparing titres in acute and convalescent sera
- serological confirmation of poliovirus infection following detection of poliovirus using molecular and/or culture-based assays
- quantifying antibody levels in individuals who work in laboratories where there is deliberate handling of poliovirus. This is a charged service.
- Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
- Probable: A clinically compatible illness with an epidemiological link.
- Confirmed: A clinically compatible illness that is laboratory confirmed.
- Not a case: A case that has been investigated and subsequently found not to meet the case definition, including cases under the age of 15 years who have been deemed to have a non-polio paralytic illness by the National Certification Committee for the Eradication of Polio.
Cases can be further classified as follows.
- Vaccine-associated paralytic poliomyelitis (VAPP) a rare event where neurological damage is caused by a virus ingested from the oral polio vaccine (OPV). A mutation of the vaccine virus known as a reversion causes previously attenuated poliovirus to revert to a more neuro-virulent form. The paralysis that results is identical to that caused by wild poliovirus.
- Wild virus-associated poliomyelitis: Any case not meeting the criteria for being vaccine associated. Such cases will be imported since New Zealand was declared free of poliomyelitis by WHO in 2000.
- Imported: A case occurring in a person who has travelled or resided in a polio-endemic area within 35 days of disease onset or who is epidemiologically linked to a person who has done so. Surveillance should be intensified at both local and national levels to detect any additional cases without delay.
- Vaccine derived poliomyelitis: Vaccine-derived poliovirus (VDPV) is the live, attenuated strain of the poliovirus contained in the OPV that has changed and reverted to a form that can cause paralysis in humans and has the capacity for sustained circulation. Vaccine-derived polioviruses differ from the parental (original) Sabin strains found in the vaccine by 1 percent to 15 percent of VP1 nucleotides. This is a measurement of genetic change that scientists use to monitor the circulation of viruses.
Spread of infection
The incubation period for polio is usually 7–14 days for infections resulting in AFP, although the reported range is 3 to 35 days.
Mode of transmission
Poliovirus is passed person to person, principally via the faecal–oral route, but potentially also via respiratory droplets.
Period of communicability
The period of communicability of the poliovirus has not been precisely defined, but transmission is possible as long as the virus is excreted. Poliovirus has been detected in throat secretions as early as 36 hours, and in faeces 72 hours, after exposure to infection. It typically persists in the pharynx for about one week and in faeces for three to six weeks. However, it may be shed in the faeces of immunocompromised people for several years. Cases are most infectious in the days immediately before and after the onset of any symptoms.
All people suspected of suffering from polio must be notified to the medical officer of health by the clinician caring for the patient, and they must be appropriately investigated.
Laboratories must immediately notify the local medical officer of health of any polio-positive VP1-based sequencing.
On receiving a notification, medical officers of health should immediately notify the Ministry of Health, including the Director of Public Health, and check that the paediatrician has notified the case to the New Zealand Paediatric Surveillance Unit (NZPSU).
There should be a higher index of suspicion if there is clinically compatible illness with an epidemiological link. The local medical officer of health is responsible for ensuring adequate isolation of the case after hospital discharge, and identification and management of the case contacts.
Ensure complete case information is entered into EpiSurv.
Under the WHO’s International Health Regulations 2005 (IHR), assessment of any suspected case of poliomyelitis must occur within 48 hours of initial identification, and any isolation of wild poliovirus must then be notified to the WHO via the National Focal Point within 24 hours of confirmation. This confirmation must have been undertaken by the WHO-accredited National Poliovirus Reference Laboratory at ESR. In New Zealand, the National Focal Point is the Office of the Director of Public Health, Ministry of Health.
Notifying cases of acute flaccid paralysis as part of the WHO global eradication programme
As part of the WHO initiative to eradicate polio, New Zealand has a programme of surveillance and investigation of all cases of AFP in children under the age of 15. Such cases are required to be reported by telephone to the New Zealand Paediatric Surveillance Unit at the Department of Women’s and Children’s Health, University of Otago, Dunedin, and to have a full clinical and epidemiological assessment and virological investigation of stool specimens. All cases are discussed by the National Certification Committee for the Eradication of Polio, and records of its deliberations are reported to the WHO.
All children with AFP should have two stool samples (or rectal swab with faecal material if stool is not immediately available) collected 24 hours apart within 14 days onset of the paralysis. These should be sent to ESR via the local laboratory, as per current AFP surveillance.
For more detailed information on AFP surveillance, see the NZPSU website.
Management of case
Early identification of other cases will help to control spread. Review of possible recent cases may provide evidence of the source of an indigenous case.
Obtain a history of vaccination, travel and contact with recently returned travellers. For poliomyelitis serology collect an acute serum specimen as early in the course of disease as possible, and a convalescent specimen should be obtained at least three weeks later. Ensure laboratory confirmation has been attempted.
Case details should be gathered as soon as possible by public health units, using the ESR case report form. Details to be included are demographic details, vaccination history, history of recent travel, immune competency, onset and range of symptoms, and type and results of laboratory tests.
Infection prevention and control considerations
Enteric precautions are required during a person’s hospital stay if polio is suspected or confirmed, and droplet precautions are required if there are pharyngeal symptoms.
When the person with polio is discharged home, they should stay at home until six weeks have passed since the onset of symptoms, or until two consecutive stool specimens taken at least seven days apart are negative for poliovirus. Contact with others should be limited but strict isolation is not necessary.
At home, a high standard of hygiene must be maintained until two clear stool specimens are obtained. Hand hygiene is the single most important means of preventing the spread of infection. After going to the toilet, all cases should wash their hands well with soap and warm water for 15–20 seconds and then dry them thoroughly, preferably with a disposable hand towel. An antiseptic hand gel, rubbed in for 15–20 seconds, is a good alternative when hands are not visibly soiled. The usual bathroom and wash facilities may be used and the surfaces disinfected with dilute bleach. Within the home, contact with others should be limited but strict isolation is not necessary.
Supportive care should be given to address symptoms. Cases of polio should be under the care of an infectious diseases paediatrician or physician.
Management of contacts
A contact is defined as any individual potentially exposed through:
- infectious faecal material, either from close physical contact or shared toilet facilities, or
- droplet spread, with a suspected or confirmed case of polio during his/her potentially infectious period.
Those at high risk of acquiring and/or transmitting poliovirus include:
- household members who live with the index case
- close social contacts – family and friends who have spent a lot of time with the index case while he/she has been infectious
- children in shared day care with the index case while he/she has been infectious
- Food handlers and childcare workers who may have had contact with the index case while he/she has been infectious.
Those at low risk of acquiring and/or transmitting poliovirus include:
- Individuals who may have had other contact with, or shared a toilet with, the index case while he/she has been infectious
- Individuals who have been consumers of food prepared by the index case while he/she has been infectious.
High-risk contacts should be sought, and ways of communicating with low-risk contacts should be determined.
General advice for all contacts
All contacts, regardless of previous vaccination, should be informed about the infection, encouraged to use good hygiene practices, and asked to report any symptoms to their medical practitioner. The local public health unit will ensure appropriate general information is given to the local primary care practitioners.
If a contact suffers from an illness with neck, back or leg stiffness, severe muscle pain or neurological symptoms, he/she should seek medical advice. The medical practitioner is advised to:
- refer the patient to hospital as a suspected case of polio
- notify the local medical officer of health of a suspected case of polio.
If a contact suffers from a minor non-specific illness (eg, fever, malaise, headache, nausea, or vomiting) or an influenza-like illness, the medical practitioner is advised to:
- test the contact for poliovirus (see ‘Laboratory testing for diagnosis’ above)
- reinforce messages about hand hygiene and disinfection practices
- emphasise the importance of seeking medical attention if symptoms worsen or neurological symptoms occur
- notify the local medical officer of health of a possible case of polio.
Additional advice for high-risk contacts
As well as the above, high-risk contacts should:
- have two stool specimens taken 24 hours apart tested for poliovirus, and a throat swab or nasopharyngeal swab if respiratory symptoms are present
- be excluded from early childhood services, school or work for six weeks after contact with a case, or until two stool specimens, at least 24 hours apart, are negative for poliovirus
- wipe down surfaces in toilet and bathroom facilities with a disinfecting solution of dilute bleach (10 ml of bleach in ½ litre water) and make a fresh solution every 24 hours
- avoid strenuous physical activity, and not undergo a tonsillectomy (as any of these might increase their risk of infection and paralysis)
- Have a primary course or booster polio vaccination (see below).
The local public health unit should regularly monitor high-risk contacts to check for the development of symptoms and provide information as needed, and inform the medical practitioner they are doing so.
Laboratory investigation of other contacts is not necessary unless they develop symptoms.
Other contacts should be advised of the importance of hand hygiene and advised to see a medical practitioner for any illness but will not be restricted.
Although there is no known post-exposure protection from polio infection, vaccination of high-risk contacts is recommended even though some contacts may already be infected at the time of vaccination.
If there is a certain history of a completed course of polio vaccination (three doses using any combination of OPV – which is no longer used in New Zealand – and IPV given at least four weeks apart), a booster dose of IPV should be offered. If in any doubt, a full primary course of IPV should be offered.
A full primary course of IPV, with at least four weeks between doses, should be offered if the person has:
- no history of polio vaccination
- an uncertain history of polio vaccination
- a history of an incomplete primary course.
OPV will not be used as part of the vaccination protocol for contacts during a polio outbreak response because (a) it is not currently available in New Zealand, (b) of the already high immunisation coverage in New Zealand, and (c) of the risk of VAPP.
For young, high-risk contacts, vaccination should be aligned with the National Immunisation Schedule, if possible, after the initial dose.
Although there are no known adverse effects on the foetus following polio vaccination during pregnancy, as a general precaution vaccination is not advised for pregnant women in the first and second trimester in a low-risk setting. However, pregnant high-risk contacts susceptible to paralytic polio should be immunised as per the vaccination protocol during a polio outbreak.
Because there is an absence of evidence on the protective role of IPV vaccination after possible exposure, contacts vaccinated need to be informed that they are not necessarily protected by vaccination, and that they should still contact a health provider if they develop any of the symptoms suggestive of polio.
In early childhood services or other institutional situations, ensure that satisfactory facilities and practices are in place for hand cleaning; nappy changing; toilet use and training; food preparation and handling; and cleaning of sleeping areas, toys and other surfaces.
- Ministry of Health. 2017. Immunisation Handbook 2017. Wellington: Ministry of Health.
- Ministry of Health. 2014. National Poliomyelitis Response Plan for New Zealand: Updated 2014. Wellington: Ministry of Health.