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THE HEALTH HAZARDS OF HEATWAVES


Author: Dr Douglas Rasbash, co-author, Boitumelo Pauline Marumo

8 February 2024


Between 28th October 2023 and February  7th 2024, The Department of Meteorological Services has issues 4 heatwave advisories, warning of temperatures in excess of 40 Degrees Celsius. While the specific risks and reactions can vary, there are some general public health hazards associated with extreme heat, and in the context of disease prevention and containment, food management and quality control. This item serves as a salutatory reminder that global warming has important and significant public health consequences that will need managing by government.  The global costs of climate change now estimated to be $400 million per day, which runs to $2.5 Trillion by 2030, are astronomical. The loss of life through malnutrition diarrhea and heat stress caused by global warming is expected to be 250,000 per year according to the WHO. These academic estimates are warnings which depend on commitments to reduce the emissions of greenhouse gases that causes the planet to heat up.



Picture by: Dr Douglas Rasbash, showing temperatures of above 40 Degrees Celsius near Gaborone, Botswana. 8 February 2024


High temperatures can lead to various heat-related illnesses, including heat exhaustion and heatstroke, which can be life-threatening. Symptoms can include dizziness, nausea, rapid heartbeat, and confusion. Hot weather can cause people to lose fluids through sweating, leading to dehydration. Severe dehydration can result in electrolyte imbalances and kidney problems. High temperatures can worsen air quality, increasing the risk of respiratory problems, especially for individuals with pre-existing conditions like asthma or chronic obstructive pulmonary disease (COPD). Extreme heat can put extra stress on the heart and circulatory system, increasing the risk of heart attacks, especially in older individuals. People with chronic illnesses, such as diabetes or hypertension, may see worsened symptoms during a heatwave. Prolonged exposure to high temperatures can lead to elevated body temperatures, which can cause a cascade of physiological reactions. The body tries to cool down by sweating, which can lead to fluid and electrolyte losses if not adequately replaced. Blood vessels may dilate in an attempt to dissipate heat, which can affect blood pressure regulation. Prolonged heat stress can weaken the immune system, making individuals more susceptible to infections, including foodborne illnesses.



In addition to disease, excessive heat challenges effective food management and quality control. During a heatwave, there is a higher risk of foodborne pathogens multiplying in food. Proper food handling, storage, and cooking are crucial to prevent foodborne illnesses. High temperatures can accelerate food spoilage. Proper refrigeration and temperature control are essential to maintain food quality. Increased demand for water during heatwaves can strain water supply systems, potentially leading to contamination issues. Contaminated water can be a source of foodborne illnesses. Extreme heat can lead to power outages (because thermal energy generation is water dependent), which can affect refrigeration and food storage. Businesses and households should have contingency plans for such situations. The higher temperature can encourage the growth of bacteria and other pathogens in food, increasing the risk of foodborne illnesses. Ensuring the safety of drinking water is critical during heatwaves. High temperatures can affect water quality, and maintaining a safe water supply is vital for food preparation and hygiene.



Increased temperatures can lead to the proliferation and increased activity of various pathogens, especially foodborne pathogens. Here are some of the most common pathogens and how higher temperatures can increase their propensity to cause illness. Salmonella is a common foodborne bacterium found in raw meat, poultry, eggs, and unpasteurized dairy products. Higher temperatures can promote the growth of Salmonella in these foods. Also, Salmonella can survive in warmer conditions, increasing the risk of contamination during food handling. Campylobacter is another common cause of foodborne illness, often associated with poultry. It thrives at higher temperatures and can multiply rapidly in warm, humid conditions. Some strains of E. coli, like E. coli O157:H7, can cause severe foodborne illness. Increased temperatures can encourage its growth in contaminated foods, such as undercooked ground beef or unwashed and rotting vegetables. Listeria monocytogenes is a bacterium that can grow at refrigeration temperatures but is more heat-resistant compared to many other pathogens. When exposed to higher temperatures, such as those found during heatwaves, it can thrive and contaminate a variety of ready-to-eat foods. Norovirus is a highly contagious virus that causes gastroenteritis. Although it is not a bacterium, it can be transmitted through contaminated food. Warmer temperatures can increase the likelihood of food handlers or consumers contaminating food with the virus. Clostridium perfringens bacterium is often associated with improperly cooked or reheated meat dishes. It forms spores that are heat-resistant, and if food is not reheated thoroughly, these spores can become active and multiply, leading to illness. Vibrio vulnificus is a bacterium found in seafood, particularly in warmer coastal waters. Increased ocean temperatures due to climate change can lead to higher levels of this pathogen in seafood.



The mechanisms by which higher temperatures increase the propensity of these pathogens include faster reproduction where many bacteria reproduce more quickly at higher temperatures, leading to increased populations in contaminated food. Warmer temperatures reduce the time it takes for pathogens to begin growing in food, making them more dangerous. Some pathogens are more heat-resistant, allowing them to survive and multiply even when exposed to heat during cooking or storage. People are more likely to mishandle food and cross-contaminate it when they are uncomfortable due to heat, which can lead to pathogen transmission. Climate change, including extreme weather events like heatwaves, can alter the distribution and behavior of pathogens. For example, it can lead to Vibrio vulnificus becoming more prevalent in previously unaffected areas.



To mitigate these risks, it's crucial to maintain proper food handling, storage, and cooking practices, especially during periods of extreme heat, and to be aware of the potential for increased pathogen activity in warmer conditions. Public health agencies and food safety authorities provide guidelines and recommendations for safe food handling to minimize these risks and how they can lead to foodborne illnesses. During a heatwave, power outages or equipment failures can result in inadequate refrigeration or freezer temperatures. Food stored at improper temperatures can lead to the growth of foodborne pathogens. Pathogens like Salmonella and Listeria can multiply in warm refrigerators, increasing the risk of contamination. Higher temperatures can lead to increased sweating and discomfort, making individuals more prone to poor hand hygiene and cross-contamination between raw and ready-to-eat foods. The impact is that Cross-contamination can transfer pathogens from raw meats to fresh produce or other ready-to-eat items, leading to food poisoning. Heatwaves can lead to a desire for lighter, no-cook meals. When people do cook, they may rush or not cook food to the proper internal temperature. Leftover food can be mishandled during a heatwave. People may leave food out for extended periods, especially when picnicking or eating outdoors. Bacteria can rapidly multiply in leftover food left at warm temperatures, leading to food poisoning when consumed later. With the discomfort of high temperatures, people may  overlook inspecting food for signs of spoilage, such as changes in colour, texture, or odour. People may not drink enough water during heatwaves, which can lead to dehydration. Inadequate hydration can impair the body's ability to fight off infections. In hot and sweaty conditions, people may neglect proper handwashing practices, which are critical for reducing the risk of foodborne illness. Food recalls and advisories related to heatwave-related food safety risks may be issued, but individuals may ignore or overlook them. Consuming recalled or advisory-affected food products can lead to foodborne illnesses as these products may be contaminated.



To mitigate these malpractices during heatwaves, it's important for individuals to remain vigilant, follow food safety guidelines, and prioritize safe food handling practices. Public health agencies and must exercise increased vigilance and should also raise awareness about the risks associated with heatwaves and provide specific guidance on food management during extreme weather conditions. Proper education, awareness, and adherence to food safety practices are essential in preventing food poisoning during heatwaves and with global warming due to climate change the risks of food poisoning will most certainly increase.

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