Poliovirus detection in Melbourne wastewater

What is the issue?

On 2 December 2024, Australia's poliovirus surveillance program detected vaccine-derived poliovirus in pre-treated sewage from the Western Treatment Plant in Melbourne. This detection is likely linked to an individual who received a live polio vaccine overseas and has continued to shed the virus since arriving in Victoria. The risk of disease transmission is considered very low, due to Victoria’s high vaccination coverage and effective sewage treatment processes and the particular characteristics of the virus detected which have been analysed in detail by the regional poliovirus reference laboratory located within the Victorian Infectious Diseases Reference Laboratory. Increased sewage sampling will continue over the coming months to monitor the situation.

Polio, or poliomyelitis, is a highly contagious viral infection that can cause paralysis and death. Australia remains polio-free, as this is not a wild-type poliovirus detection. Vaccine-derived poliovirus has been detected in wastewater in several regions globally this year, including Europe. In countries where polio has been eradicated, the importation of the virus through unvaccinated or inadequately vaccinated individuals remains a concern. Immunisation is the best protection against polio. This detection is a reminder to keep up to date with your polio immunisations.

Polio immunisation coverage in Victoria is extremely high with 95 per cent of children at five years of age protected – above the national average. However, childhood immunisation coverage has declined since 2021 and some populations in Victoria have lower coverage.

Australia continues to monitor poliovirus through wastewater surveillance to detect its presence in the environment. This program provides critical data to the World Health Organization in its efforts to eradicate poliovirus worldwide. The detection of vaccine-derived poliovirus in Victoria, albeit in tiny amounts, demonstrates that routine environmental testing is effective.

Who is at risk?

Children and adults who have not been fully vaccinated against polio are at greatest risk if exposed to an infected person. People travelling to polio-endemic or epidemic regions should receive a polio booster vaccine every 10 years.

The presence of virus in sewage does not present any risk to residents of Melbourne, as sewage undergoes a thorough treatment process.

Symptoms and transmission

The poliovirus is spread from person-to-person through the faeces (poo) or saliva of an infected person. A person may develop symptoms within 4 – 35 days (typically 7 – 10 days) of coming into contact with the virus. Many people infected with poliovirus have no symptoms, others may present with a non-specific febrile illness (symptoms may include fever, tiredness, headache, muscle stiffness, nausea and vomiting). Less than 1% of people who catch poliovirus develop severe muscle weakness, also known as acute flaccid paralysis (AFP).

Recommendations

For health professionals

Encourage vaccination:

• Promote polio vaccination particularly in under-immunised cohorts and those travelling to endemic and high-risk countries.
• The polio vaccine is available for free on the National Immunisation Program (routinely given at 2, 4, 6 months of age, and at 4 years of age), and for catch up vaccinations for people aged under 20 years of age or refugees and humanitarian entrants of any age.
• For further information, please refer to the Australian Immunisation Handbook.

Who to test:

Clinicians should consider polio in patients who present with:

• Acute flaccid paralysis (AFP), defined as acute onset of weakness in one or more limbs or the acute onset of bulbar paralysis; or
• Symptoms consistent with abortive poliomyelitis (fever, headache, sore throat, listlessness, anorexia, vomiting, abdominal pain) or non-paralytic poliomyelitis (also displaying meningeal irritation); or
• Febrile illness AND history of travel to, or contact with persons from an endemic country in the 21 days prior to illness onset

Clinicians are required to report and submit stool samples from any cases of AFP in children less than 15 years of age, even where poliovirus infection is considered a highly unlikely diagnosis, as part of the Australian poliovirus surveillance program.

How to test:

• Two stool specimens collected more than 24 hours apart, and a throat swab or nasopharyngeal aspirate (if lumbar puncture is performed CSF should also be sent for testing).
• All specimens from suspected polio and AFP cases should be sent directly to the National Enterovirus Reference Laboratory (NERL) at the Victorian Infectious Diseases Reference Laboratory. The procedure and Laboratory Request Form for referring stool specimens to the NERL are available at: https://www.vidrl.org.au/surveillance/afp-surveillance1/.
• Consult with the NERL for further advice on testing.

Advice and notification:

• Notify all suspected or confirmed cases of poliovirus infection urgently to the Department of Health by calling 1300 651 160. Do not wait for test results.
• Isolate suspected and confirmed cases with contact precautions and exclusive toilet access.
• Consult your Local Public Health Unit and Infection Prevention and Control team for additional public health and infection control measures.

For the general public

• The polio vaccine provides safe and effective protection against polio. Ensure that you and your family are up to date with all routine immunisations.
• Anyone planning overseas travel should make sure they have received appropriate travel vaccinations.
• For further information, speak to your immunisation provider.