Overview 

The profound environmental impacts of global climate change significantly reshape the dynamics of food-borne diseases, including those caused by bacteria such as Listeria monocytogenes (L. monocytogenes). Although Listeria species are widely distributed in nature, certain aspects of their epidemiology and characteristics render them particularly sensitive to climate variations. Notably, ambient temperature increases and precipitation alterations have been associated with spikes in listeriosis cases, echoing trends observed in other diarrheal pathogens.¹ 

Listeriosis, an infectious disease caused by the bacterium, predominantly affects vulnerable populations, including the elderly, immunocompromised individuals, and pregnant women.² Classified as a zoonosis, listeriosis was first identified as a foodborne infection in the 1980s.³

Despite being less common than other foodborne diseases, listeriosis has a high mortality rate even with prompt and appropriate treatment. The infection can present a variety of symptoms, from mild febrile gastroenteritis to severe invasive diseases such as bacteremia, sepsis, and meningoencephalitis.²

Epidemiology of listeriosis 

Listeriosis is a notable foodborne illness with a broad epidemiological impact. This bacterium, widely distributed in nature and found in the faecal flora of many mammals, poses a significant risk through contaminated food consumption. The bacterium contaminates a range of food products, including meat, vegetables, seafood, unpasteurised milk, and certain dairy products, highlighting the need for stringent food safety measures to mitigate its dissemination and impact on public health.² 

The incidence rates vary between three to six cases per million per year, with neurolisteriosis, bacteraemia, and maternal-neonatal infections found to be the most predominant forms .^3,4 Epidemiological studies have identified various host risk factors, including older age, immune deficiencies, malignancies, HIV infection, cirrhosis, diabetes, alcoholism, and immunosuppressive therapies.³ L. monocytogenes' ability to thrive in adverse conditions, such as a wide pH range, high salt concentrations, and temperatures between −2°C and −42°C, raises concerns, particularly in the food industry. The incubation period of listeriosis varies widely, from 1 to 70 days, with reports suggesting longer periods in certain cases.¹

Climate change and L. monocytogenes 

Climate change can cause heightened temperatures, altered precipitation patterns and more frequent and intense extreme weather events such as storms, heatwaves, floods, and droughts.⁵ Climate change exacerbates the risks associated with L. monocytogenes in several ways:

Hot Weather Extremes: It is well documented that listeria cases peak during the warmer summer months.⁶ Increased ambient temperatures accelerate the replication of the bacterium.¹ Moreover, it is more difficult to maintain the safe temperature of perishable food products during storage, transportation, and distribution, leading to higher bacterial loads on food products.^1,6

Food Processing and Storage: Water scarcity impacts hand hygiene and the cleanliness of food processing equipment. Incomplete cleaning can allow the bacterium to persist in hard-to-reach areas of machinery used for food processing. This is especially dangerous given that the bacterium can tolerate high salt and nitrate concentrations, desiccation, moderate heat, and both acidic and alkaline conditions, and thus machinery requires deep cleaning. 

Water Source Changes: Additionally, changes in water sources introduce alternative opportunities for contamination. Indeed, climate change often impacts potable municipal water, with increased temperatures and altered precipitation patterns leading to droughts, reducing the availability of freshwater sources. This scarcity can put a strain on municipal water supplies, making it necessary for farmers to use surface water for irrigation which is more likely to contain L. monocytogenes.¹ Indeed, a study of rainwater tanks in villages in three provinces of South Africa found that 22% of samples were contaminated with the bacterium.⁷

Rainfall and Runoff: Short bursts of rainfall, specifically lasting 5 to 10 minutes, can facilitate the dispersal of L. monocytogenes from soil to plants.⁸ Prolonged downpours, which can wash away pathogens, are less common as a result of climate change. Contaminated runoff can affect the water used in fish farms and produce, leading to the contamination of fish and vegetables and the subsequent introduction of the bacterium into food processing plants.¹

Public Health Infrastructure: Climate change can strain public health systems, making it challenging to respond to and manage listeriosis outbreaks. This includes impacts on disease surveillance, food safety inspections, and healthcare services.⁹

The nexus between climate change and L. monocytogenes underscores the need for enhanced food safety measures, improved water management practices, and robust public health infrastructure to mitigate the increased risks posed by a changing climate.¹⁰

Summary 

Overall, the intersection of climate change and L. monocytogenes presents heightened risks for food safety and public health. With global temperatures rising and precipitation patterns becoming increasingly erratic, the conditions for L. monocytogenes proliferation are becoming more favourable. As countries worldwide grapple with the impacts of climate change, particularly those with conditions conducive to L. monocytogenes proliferation, proactive measures are crucial.

FAQs

What is climate change? 

There are many different definitions of climate change. Climate change generally refers to long-term alterations in the average weather patterns that have come to define Earth’s local, regional, and global climates. It encompasses a broad range of phenomena, including shifts in temperature, precipitation patterns, and the frequency and intensity of extreme weather events. This has widespread environmental, social, and economic implications.

What is driving climate change?

Climate change is driven by a combination of natural processes and human activities. However, the current rapid changes in the Earth's climate are predominantly caused by human activities.⁵ The key human drivers include: burning fossil fuels, deforestation, industrial processes, urbanisation and agricultural practices (particularly livestock farming).¹¹ 

What countries are particularly at risk?

Countries at risk of the nexus between listeriosis and climate change typically experience significant climate change impacts and have conditions conducive to the proliferation of L. monocytogenes.

These countries include: South Africa, Nigeria, India, Bangladesh, Vietnam, Philippines, Brazil, Mexico, Spain, and the United States 

What measures are being put in place to slow climate change? 

To slow climate change, a range of measures are being implemented globally across various sectors. Key measures include international agreements like the Paris Agreement, which was negotiated by 196 parties, to keep global temperatures below 2 above pre-industrial levels.¹² Renewable energy sources such as solar, wind, hydropower, and geothermal are being expanded, while energy efficiency is being improved through better building codes and appliance standards.