Changes in climate and weather patterns worldwide are converging with social trends, shifting populations, land use change, and increasingly impaired water infrastructure to dramatically make life worse for those across the globe. We now have evidence that climate is a major factor increasing risks for food and waterborne diseases. While the linkages are complex, both temperature and precipitation are directly and indirectly associated with illnesses. It is critical to improve infrastructures and apply appropriate interventions to prevent climate-related risks to public health in water and food.
Climate change affects both water quality and food safety, which will both have important impacts on public health in the absence of appropriate interventions.
The National Institute of Environmental Health Sciences notes that the potential effects of climate change on food-related illness may be indirect and moderate or unlikely in the US. On a global scale, however, the concern may be greater, arising from:
1. The direct correlation between water temperatures and certain microorganisms that cause human gastroenteritis.
2. Direct and indirect links between food contamination, certain foodborne disease outbreaks, and earth surface temperatures.
3. Possible changes in food production patterns due to climate—temperature, precipitation, humidity, and flooding are all factors in pathogen contamination.
Evidence from more than 100 articles found that heavy rainfall, flooding and severe storms were associated with the outbreaks. These scientific articles examined water-related weather events and waterborne outbreaks between 1910 to 2010. More than half were linked to drinking water contamination. Leptospira, hepatitis and norovirus and Cryptosporidium were all found to be important pathogens to consider during high precipitation and flooding events.
Nowhere is the evidence for public health risks more apparent than in Haiti. Four years after the country’s devastating earthquake, cholera, a waterborne disease driven by rains and poor sanitation, remains a critical problem. We have seen this before. Cholera increased in Guatemala almost ten-fold after Hurricane Mitch in 1998, and the seasonal pattern of the disease in Bangladesh is also evident.
In addition, climate transition from one extreme to another may represent the highest public health risk. In March 2006, for example, a cycle of drought and flood in Malawi was reported to aggravate a cholera outbreak with many deaths and over 4,000 cases due to poor sanitation recorded during the disaster.
In the US there is compelling scientific evidence that climate is a driver of waterborne disease. More than half of community outbreaks in the US were associated with extreme rain events. Heavy rains have been linked to increases in Legionellosis, wound infections, respiratory diseases and conjunctivitis. While most studies have revealed that greater volumes of precipitation are a risk, one project in England and Wales showed that 10 percent of outbreaks were associated with 14 days of dry weather with the suggestion that sewage discharges into rivers during droughts pose a risk to public health.
Studies in Alaska suggested that warmer temperatures may be impacting the spread of diseases transmissible from animals to people where subsistence hunting is common. This may be associated with the ability of infected animals to survive winters in larger numbers, increasing transmission risk.
Microbial and chemical toxins in food
Food safety involves ensuring that the food supply is free of pathogens and chemicals that could harm human health. The contaminants of greatest concern can roughly be divided into microbial agents and chemical toxins. Well-known microbial pathogens related to foodborne disease include norovirus, E. coli, Salmonella, Listeria, Vibrio spp., and Campylobacter. Common food contaminants include mycotoxins (fungal toxins) such as aflatoxin, phycotoxins (algal toxins) such as cyanotoxins, arsenic, lead, dioxins, and pesticides.
The presence of some toxins in food is likely to increase with changing climate trends. Aflatoxin is an example. It is a mycotoxin common in maize, peanuts, tree nuts, and cottonseed grown in warm climates. It is the most potent human liver carcinogen known, and synergizes with chronic hepatitis B virus infection to greatly increase the risk of liver cancer.
Mycotoxins are metabolites of fungi that have toxic and carcinogenic effects on the animals and humans that consume them. In the near future, there is reason to believe that climate change trends may result in higher levels of certain mycotoxins in crops. The fungi that produce aflatoxins are more likely to create toxins in warmer temperatures. Moreover, warmer temperatures combined with greater extremes in precipitation or drought increase plant stress. This predisposescrops to fungal infection and mycotoxin contamination.
Phycotoxins are produced by algae that can contaminate shellfish such as lobsters, oysters, clams, and mussels; or can be inhaled in the event of harmful algal blooms (HABs) and wind currents directed toward humans.
As with mycotoxins, the presence of phycotoxins is dependent on climatic factors. Typically, warmer weather encourages the HABs that can produce large amounts of phycotoxins, which can then contaminate shellfish.
Measures to address waterborne and foodborne disease
Understanding the climate linkages to these public health risks has facilitated the development of risk assessment and management strategies. Quantitative microbial risk assessment (QMRA) is a framework used to address management of food and waterborne disease and also to mitigate the impact of climate change on waterborne diseases. Critical to this method is understanding the source of the pathogens, their concentrations, their persistence and finally their transport to drinking, recreational waters, shellfish waters, irrigation waters and to the food system.
Climate change poses several challenges to water management strategies including extreme events, dwindling water supply, and the increasingly incorrect assumption that the past will accurately predict future conditions. Extreme weather events are likely to increase and droughts are spreading across the western part of the US. This means that communities must have emergency response plans in place for natural disasters such as hurricanes and floods and ultimately plan for purifying wastewater to mitigate both scarcity and pollution.
It is possible to estimate population risk through predictive models that link climate variables with concentrations of mycotoxins and phycotoxins in foods. The results can be used to predict human exposures to toxins of concern. Ultimately, increasing dietary diversity and moving away from the staple foods that are frequently contaminated with mycotoxins or phycotoxins, may prove the most sustainable methods of reducing foodborne toxin exposure to humans.
Prior to the 1980s, for example, residents of Qidong, China, subsisted primarily on maize grown under environmental conditions that led to high aflatoxin contamination. By turning from maize to rice and other foodstuffs, liver cancer there decreased by 45 percent since the 1980s.
Such interventions, along with policies to address climate change-related risks of waterborne and foodborne pathogens and toxins, will provide greater public health reassurance in the coming generations for the availability of safe food and water.