Food Safety & Risk Analysis Update - May 2024

9th May 2024

Food Safety & Risk Analysis Update - May 2024

Welcome to this edition of our Food Safety Update. 

The first topic discusses flooding and food safety, the second topic covers Listeria.


Flooding and Food Safety

It has now been over a year since the Auckland floods, and Cyclone Gabrielle wreaked havoc on the North Island.  While life appears to be back to normal, is it really?


Flooding adversely affects fresh produce safety - Read here

The above article, written by Dr. Sukhvinder Pal Singh (Senior Research Scientist, NSW Department of Primary Industries) and published in October 2023, focuses on how flooding can exacerbate the microbial food safety risks in the primary production and processing of fresh produce and briefly describes the management strategies. While the author based his findings on Australian data, the scenario is not dissimilar to New Zealand. The floods of 2023 reinforce these messages.

‘Flooding is the most recurring and common natural disaster affecting society, food security and the environment. Floodwater is known to be a carrier of biological, chemical and physical hazards affecting food safety during primary production and processing of fresh horticultural produce.’

The short-term effects of flooding are obvious and crucial to manage immediately to mitigate loss, but what of the longer term?

‘However, the long-term impacts of recurring flooding are far more severe and damaging due to the survival and persistence of microbial pathogens in soils, water sources and processing environments.’

The article makes some very interesting points regarding die off rates for pathogens in various soil types and variable conditions, and that the lack of knowledge in this area limits the advice available to growers trying to manage the potential for contamination following a flood. How long before any of the available water is safe to use for anything to do with the business of growing when the potential for contamination appears almost unavoidable?  The author points to the US FDA guidance on evaluating the safety of food affected crops as being a good example to follow.

‘Conducting thorough risk assessments of flood-prone areas and implementing appropriate mitigation strategies are important strategies to manage flooding risks. Improving water and flood management systems, such as proper drainage and irrigation practices are critical. Enhancing hygiene practices during harvesting, processing and transportation of fresh produce along with regular testing and monitoring of water sources used in preharvest and post-harvest operation are among the practical management options.’

In short, mitigation of the effects of flooding on fresh produce safety begins before the flood and continues until the next one. The importance of good hygiene practices along with regular testing and monitoring of any water used for any process during the production (from planting to retail) of fresh produce cannot be understated.

United Fresh, with Apples & Pears & Vegetables NZ, is supporting a project called Post Flood Decision Making by Grower: Is the soil safe for planting?  This is managed by NZ Food Safety Science & Research Centre with ESR as the lead researcher. This will assist in answering some of the difficult questions we are increasingly faced with and offering decision-making tools for the future. The aim of this research is to complement some of the work undertaken looking at land rehabilitation post Cyclone Gabrielle. This will be completed in August – September of this year.

United States Food and Drug Administration (2011) Guidance for industry: evaluating the safety of flood-affected food crops for human consumption. ( )



Here’s a brief rundown on why listeria is of concern to the industry:

  • It is a relatively rare disease.
  • The high rate of death associated with this infection makes it a significant public health concern, especially for the young, the elderly, the immunocompromised and pregnant women i.e. a large proportion of our population.
  • Unlike many other common foodborne pathogens causing bacteria, L. monocytogenes can survive and multiply at low temperatures usually found in refrigerators.
  • L. monocytogenes are ubiquitous in nature and found in soil, water and animal digestive tracts.
  • Fresh produce may be contaminated through soil or the use of manure as fertilizer.
  • Changes in food trends has potentially increased the risk of listeria infections.


Foodborne disease: how are we tracking? - Food New Zealand magazine article - Read here

A commentary by Distinguished Professor Phil Bremer on the NZFRSSC Annual Report of Foodborne Disease 2022 had this to say about listeria:

‘It was notable that the incidence of listeriosis has not decreased over the last 20 years despite extensive efforts by food producers, regulatory authorities, and researchers to reduce the incidence of L. monocytogenes in processed foods.’ 

He also noted that all cases were attributable to food sources, and given the effort put into reducing incidences, it is interesting to speculate why this is not resulting in a reduction in the occurrence of the disease.  One reason could be diet-related, perhaps due to an increase in the consumption of raw/ natural/ unwashed/ uncooked foods.

Changing consumptions patterns as consumers become more health and environment conscious has major implications for the Fresh Produce industry.  An example is berries – fresh or frozen – used unwashed, uncooked in smoothies.  Another is people eating kiwifruit skins as a matter of course.

Understanding how difficult it is to manage how pathogens such as listeria enter a packing environment and survive is critical at the planning stage for pack houses and also for developing cleaning and monitoring programmes.

In short, listeria is out there, it is hard to eradicate once established. Good hygiene and HACCP systems with a strong monitoring program are essential to ensure that the current level of incidence remains, at the very least, stable.

In the coming months (August-September), a workshop focused on Listeria will be presented by the New Zealand Food Safety, Science, Research Centre (NZFRSSC) In Auckland. 

The workshop will have a fresh produce component to it. We are hoping that NZFRSSC members and Affiliates including members of United Fresh and Horticulture NZ can attend. The workshop will be suitable for Food safety professionals in the fresh produce industry. 

We will keep you updated.