Australia is currently in the midst of a listeriosis outbreak, linked to rockmelons. Four people have tragically lost their life (as of March 2018) with a total of 17 cases identified so far. This is a terrible situation for all involved, including those directly affected, as well as food producers and the community in general.
What is listeriosis?
Listeria monocytogenes is the causative agent of the food-borne life-threatening disease listeriosis (Vivant et al 2013). Health effects range from flu-like symptoms with vomiting and diarrhoea in healthy adults to life-threatening diseases such as meningitis and septicaemia in vulnerable people and spontaneous abortion in pregnant women (Vivant et al 2013). The most common transmission route of L. monocytogenes to humans is via the consumption of contaminated food.
The growth and survival of L. monocytogenes is influenced by a variety of factors. In food these include temperature, pH, water activity, salt and the presence of preservatives (Food Standards Australia New Zealand 2013). The temperature range for growth of L. monocytogenes is between -1.5 and 45°C, with the optimal temperature being 30–37°C. (Food Standards Australia New Zealand 2013)
It has been isolated from domestic and wild animals, birds, soil, vegetation, fodder, water and from floors, drains and wet areas of food processing factories. (Food Standards Australia New Zealand Publications - May 2013).
Cattle and small ruminants are reservoirs of L. monocytogenes. There is a body of evidence that suggests that farming practices can directly impact on the circulation and implantation of L. monocytogenes. (Vivant et al 2013)
L. monocytogenes and water
The Australian Drinking Water Guidelines, the Australia Guidelines for Water Recycling and the ANZECC Australian and New Zealand Guidelines for Fresh and Marine Water Quality are very ‘light’ on guidance for Listeria spp.
ADWG and AGWR do not mention listeria explicitly, the ANZECC guidelines Irrigation and general water uses, stock drinking water, aquaculture and human consumers of aquatic foods, Primary Industries — Rationale and Background Information identifies L. monocytogenes as a biological contaminant important for the protection of human consumers of fish and other aquatic organisms.
Source water characterisation, risk assessment, health-based treatment targets assessment and validation testing are all essential components to proving that waster is safe for the use, and that pathogens are reduced to acceptable levels or removed completely, depending on the use.
L. monocytogenes in sewage sludges
The food borne pathogens L. monocytogenes has been found to be widely distributed in agricultural environments, including soil and organic amendments and products. Their occurrence in organic amendments can be frequent. The incidence of L. monocytogenes in organic fertilisers made from sewage sludge is as high as 60–73%.
A number of studies have found that the use of organic amendments for soil fertilization may therefore introduce L. monocytogenes populations in the crop environment which may subsequently be transferred to plant produce and consequently constitute a health hazard for consumers (Giradin et al 2005). Oliveira et al (2011) concluded that contaminated compost and contaminated irrigation water can play an important role in the presence of foodborne pathogens on vegetables.
State governments have prepared guidelines for the treatment of composting materials to make them safe for the uses.
Overview of Recent Outbreaks
South Africa 2017 – 2018
South Africa is currently in the middle of the biggest listeria outbreak ever seen, according to the UN World Health Organisation (WHO). The South African listeria outbreak has killed 180 people since January 2017, with nearly 1,000 cases reported. The outbreak is ongoing since January 2017 and unresolved as yet (February 2018). Deli meats, including polony and sausages, have been identified as the source. The disposal of these products is also problematic and is now also consider a hazardous waste.
USA October 2011 - Multistate Outbreak of Listeriosis Linked to Whole Rockmelons, Colorado USA
In total, 33 deaths from outbreak-associated cases of listeriosis have been reported. In addition, one woman pregnant at the time of illness had a miscarriage. The method of how the listeria bacteria first came to be in the plant remains unknown, as the soil on the farm was determined to be clear of the bacteria. It is suspected, however, that a "dump truck used to take culled melons to a cattle farm could have brought bacteria to the facility. The USA FDA found that the producer had violated FDA guidelines on the safe production of rockmelons. The greatest infractions being the decision not to chlorinate the water used to wash the rockmelons and the use of improper equipment in the packinghouse
Canada 2008 Cold Cut Deli Meat
In 2008, a widespread outbreak of listeriosis originated from a deli meat processing facility in North York, Ontario which caused infection in 57 people and resulted in 23 deaths. Since the bacteria travelled through deli meats, which are cooked (and as a result are usually free of pathogens), the contamination likely occurred during packaging.
Food Standards Australia New Zealand. (2013). Listeria monocytogenes [online] Available at: https://www.foodstandards.gov.au/publications/Documents/Listeria%20monocytogenes.pdf
Food Stuff South Africa (2018) Latest Update On SA’s Deadly Listeria Outbreak https://www.foodstuffsa.co.za/sas-listeria-outbreak-need-know/
Girardin, H., Morris, C., Albagnac, C., Dreux, N., Glaux, C. and Nguyen-The, C. (2005). Behaviour of the pathogen surrogates Listeria innocua and Clostridium sporogenes during production of parsley in fields fertilized with contaminated amendments. FEMS Microbiology Ecology, 54(2), pp.287-295.
Oliveira, M., Usall, J., Viñas, I., Solsona, C. and Abadias, M. (2011). Transfer of Listeria innocua from contaminated compost and irrigation water to lettuce leaves. Food Microbiology, 28(3), pp.590-596.
US Food and Drug Administration (2017) Update on Listeria monocytogenes and Cantaloupes https://www.fda.gov/Food/FoodborneIllnessContaminants/ucm455939.htm
Vivant, A., Garmyn, D. and Piveteau, P. (2013). Listeria monocytogenes, a down-to-earth pathogen. Frontiers in Cellular and Infection Microbiology, 3.