Food safety warnings for Listeria in New Zealand appear to be working according to a study on the burden of the pathogen in pregnant women and their babies.

The research found low rates of the infection indicating the messages could be helping to prevent cases of miscarriage, still birth, and meningitis in babies infected in the womb. However, in those who contract the infection, 12 unborn babies died and more than 100 people were hospitalized during a two-decade period.

about 20 to 40 cases of listeriosis are reported every year in New Zealand.

The study by researchers at University of Otago, Christchurch, found disproportionately high levels of the infection in mothers and babies listed as Pacific Islanders. The reason for this is unknown but warrants investigation and potentially a different food safety approach from authorities, according to the researchers.

Listeria is most commonly transmitted by consuming contaminated food. Pregnant women are about 18 times more likely to develop infections compared to the general population. Symptoms usually appear within two to 30 days of eating or drinking contaminated foods or beverages, but it can take up to 70 days in some cases.

University of Otago, Christchurch, medical student Emma Jeffs led the research and was supervised by associate professor Tony Walls, a pediatric infectious disease expert.

Jeffs studied data between 1997 and 2016 on cases of the notifiable disease in pregnant women and children. Across the two decades, there were 143 cases of listeriosis. Of those, 115 were pregnant women and 28 were children. Of all infections, 118 led to hospitalization.

The study indicates pregnant women seem to be following the Ministry of Health’s recommendations to avoid eating foods such as uncooked, smoked or ready-to-eat fish or seafood, salads, deli meats or unpasteurized raw milk products.

Researchers identified eight cases of still birth and four of miscarriage in women hospitalized by Listeria infections. Infected expectant mothers were involved in more than 30 cases of early delivery or fetal distress. There were 12 cases of children infected with Listeria who developed meningitis because of lowered immune resistance.

The study was funded by Cure Kids, a registered charity in New Zealand, and presented at the One Health Aotearoa Symposium in Wellington this past month. A breakdown of the rate of Listeria infection in pregnant women and children, by ethnicity, is as follows:

• 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)