Eating shellfish contaminated by marine biotoxins, bacteria, viruses or chemicals may cause serious illness.

Shellfish are a high-risk food because they may grow in contaminated (unsafe) water where they filter and accumulate biotoxins, bacteria, viruses, and chemicals from their surroundings. They are often eaten without being cooked. People who eat contaminated seafood can become seriously ill.

Shellfish and seawater samples around New Zealand are regularly tested to ensure they are not contaminated with biotoxins, and public warnings are issued when shellfish are not safe to eat. Biotoxins are toxins or poisons produced by algae that live in seawater and can ‘bloom’ or massively increase, when conditions are favourable.

Auckland Regional Public Health Service advises people not to eat shellfish gathered from urban areas because of the risk from illegally dumped contaminants, animal waste, road runoff, industrial discharges, leaching from buried materials and sewage overflows.

Our recommendations are:

  • don’t gather shellfish if there are warning signs posted
  • don’t gather shellfish within 28 days of a nearby sewage overflow
  • don’t gather shellfish from beaches with a history of poor water quality
  • don’t gather shellfish after heavy rain and storms, as rain may flush sewage residues or farm run-off into waterways
  • only gather shellfish from areas where the seawater is visibly clean and there are no obvious sources of contamination such as:
    • sewage outfall pipes
    • farm animals, especially at dairy farms
    • stormwater outlets, pipes or culverts
    • industrial areas
    • homes – particularly if they are on septic tanks
    • where boats may discharge on-board toilets.

Cooking shellfish at boiling point for several minutes will destroy most harmful bacteria and viruses, but not biotoxins or chemicals. Shellfish eaten undercooked or raw will still be risky to eat.

There are four main kinds of toxic shellfish poisoning. The chemicals that cause toxic shellfish poisoning are produced by certain species of algae and released into the shellfish when they filter large numbers of algae as food.

The most common and dangerous of these types of toxic shellfish poisoning is called paralytic shellfish poisoning. The symptoms of paralytic shellfish poisoning include:

  • numbness and tingling around the mouth, face, hands or feet
  • difficulties in swallowing or breathing
  • dizziness, double vision
  • in severe cases, paralysis and not being able to breathe.

Symptoms usually occur within 12 hours of eating the contaminated shellfish.

If you get sick after eating shellfish:

  • phone Healthline for advice on 0800 611 116, or see your doctor or practice nurse
  • advise Auckland Regional Public Health Service on (09) 623 4600
  • keep any leftover shellfish for testing.

ARPHS will investigate cases of toxic shellfish poisoning, liaise with other agencies and issue public warnings, as appropriate to the nature and scale of the incident.

The Ministry for Primary Industries (MPI) tests shellfish and seawater samples regularly to check if they are contaminated with biotoxins. If marine biotoxin levels in shellfish are found to be unsafe, MPI advises the public.

General questions on environments at a particular beach can be directed to Auckland Council’s environmental health officers for the particular area (09) 3010101. There may also be related information on the Safeswim website.

Last updated 23.11.2018

For health advice call Healthline for free anytime on 0800 611 116
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