Food safety warnings appear to be keeping cases of listeria reassuringly low amongst most Kiwi mothers but worryingly higher levels amongst Pacific mothers and their babies, a study has found.

A Christchurch-based University of Otago medical student examined the notified cases of listeria amongst pregnant women and children between 1997 and 2016 and found 143 cases –  the vast majority (80%) in pregnant women – 118 of the cases resulted in hospitalisation.

Emma Jeffs

Emma Jeffs, who did the study as a summer studentship under supervision of paediatric infectious disease expert Associate Professor Tony Walls, found that listeria led to eight cases of still birth and four cases of miscarriage to mothers hospitalised by listeria over the two decade period. In a further 30 cases listeria was involved in more than 30 cases of expectant mothers having early deliveries or foetal distress. There were also 12 cases of children infected with listeria who developed meningitis.

Jeffs says the study indicates pregnant women on the whole seem to be following the Ministry of Health food safety recommendations to avoid the disease.

Listeria is a foodborne bacteria and infection with listeria bacteria causes a food poisoning-like illness called listeriosis.  In healthy adults and children listeria usually causes few or no symptoms but pregnant women and their unborn babies, newborns, people with weakened immune systems and frail older people are particularly vulnerable to listeria and can be at risk of severe disease and  deaths. In pregnant women it can cause miscarriage or still birth. It can also cause meningitis in babies infected in the womb and international research has found that about half of very young infants infected with listeria will not survive and those that do survive are likely to have life-long negative health consequences.

Food safety procedures aim to prevent listeria getting into food but some foods are more at risk of being contaminated with the bacteria (see list below) so pregnant women and other vulnerable people are recommended to avoid these foods.

The risk of listeria to pregnant woman and their babies was highlighted by a high profile court case in 1992 against a mussel company following the death of unborn twins whose mother ate listeria-contaminated mussels.

Jeffs said women and children identifying as Pacific Island ethnicity had the highest incidence of disease notification and hospitalisation. The reason for this disparity was unknown but she said it warranted further investigation, and potentially a different food safety approach from relevant authorities.

Following is a breakdown of the rate of listeria in pregnant women and children, by ethnicity:

  • European pregnant women = 0.29 cases per 100,000 (40 cases)
  • Pacific Island pregnant women = 2.15 cases per 100,000 (31 cases)
  • Maori pregnant women = 0.36 cases per 100,000 (11 cases)
  • Asian pregnant women = 0.94 cases per 100,000 (23 cases)

Foods that are unsafe for people at risk of severe listeria infection include:

  • uncooked, smoked or ready-to-eat fish or seafood, including oysters, prawns, smoked ready-to-eat fish, sashimi or sushi
  • paté, hummus and tahini-based dips and spreads
  • cold pre-cooked chicken
  • processed meats including ham and all other chilled pre-cooked meat products including chicken, salami and other fermented or dried sausages*
  • pre-prepared, pre-packaged or stored salads (including fruit salads) and coleslaws
  • raw (unpasteurised) milk and any food that contains unpasteurised milk*
  • soft-serve ice creams
  • soft, semi-soft or surface-ripened soft cheese (eg, brie, camembert, feta, ricotta, roquefort).*

* Note that the foods on this list are safe to eat if heated thoroughly to steaming hot (ie, above 72°C) where appropriate.

Source : Ministry of Health

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