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Mean concentration of E. coli and enterococci (CFU/100ml) in sampled European bathing water with and without prior heavy rains

Source: EEA, based on analysis of Bathing Water Directive water quality samples (taken between 2008 and 2022 once a month during the bathing season, i.e. March-October, depending on the bathing site) and Copernicus ERA5-Land hourly precipitation reanalysis data

Note: Prior heavy rains are defined as rainfall >20mm/day occurring within 3 days before sampling

Health issues

High temperatures, altered precipitation patterns and extreme weather events can directly impact the distribution, transmission and persistence of pathogens in the environment, influencing the incidence and spread of climate-sensitive infectious diseases. People can get infected via ingestion of contaminated water or food, skin contact, or inhalation of water droplets. Infection risks are associated with viruses such as norovirus, rotavirus and hepatitis A; bacteria such as toxin-producing E. coli, Salmonella spp. and Campylobacter spp.; and Cryptosporidium spp., causing parasitic infections. Sporadically, leptospirosis, shigellosis, giardiasis and Legionnaires’ disease infections occur (ECDC, 2021). Different pathogens can cause various diseases that trigger gastro-intestinal symptoms or skin infections (EEA, 2020). Also cyanobacteria (mostly in freshwater), algae (in marine waters) and Vibrio bacteria (in brackish or marine water) can be harmful when humans are in contact with their toxins via skin contact, via accidentally ingested contaminated bathing water, or via infected drinking water or seafood. These pathogens can cause wound, skin and eye infection, allergy-like symptoms, gastrointestinal diseases, liver and kidney damage, neurological disorders and cancer (Melaram et al., 2022; Neves et al., 2021).

Observed effects

Flooding

More frequent and intense flooding may heighten exposure to pathogens from contaminated water or debris, which can contain animal faeces or carcasses, sewage and surface run-off. Standing water post-flood creates new zones for pathogen exposure, which may also contaminate cultivated crops (Weilnhammer et al., 2021). Disruption of potable water supplies may result in improper hygienic practices or contamination of water sources and contribute to the transmission of diseases, especially from private wells. Also, in post-flood cleanup efforts and temporary shelters, where the high density of displaced people and disruption of healthcare may facilitate the spread of infectious diseases, infection risks are raised (ECDC, 2021). Post-flood disease outbreaks, particularly via contaminated food and water, can escalate mortality rates by up to 50% in the first year following a flood (Weilnhammer et al., 2021). Throughout Europe, several flood-related disease outbreaks and cases have been reported (e.g., leptospirosis cases linked to cloudburst event in Copenhagen in 2011 (Müller et al., 2011), cryptosporidiosis outbreak among children after flooding in Germany in 2013 (Gertler et al., 2015), gastrointestinal and respiratory diseases after pluvial flooding in the Netherlands in 2015 (Mulder et al., 2019).

Flood-related disruption to power plants or water supply networks can affect food storage and preparation and increase the risk of foodborne diseases, especially in warm weather.

Droughts

Droughts can worsen water quality, promoting pathogen growth and increasing heavy metal and pollutant concentrations. Water scarcity may force cuts in public water supply and the use of untreated water for irrigation, elevating the risk of foodborne diseases such as STEC (Semenza et al., 2012). Moreover, an insufficient supply of water may lead to lower hygienic standards in the food-processing industry and cause an increased risk of foodborne diseases (Bryan et al., 2020).

In bathing water, reduced water levels during dry spells raise pathogen concentrations in bathing waters (Mosley, 2015; Coffey et al., 2019). Indirectly, drought-induced water conservation practices concentrate pollutants in wastewater, overwhelming treatment plants and increasing waterborne disease risks due to higher concentrations of certain pathogens (e.g., Giardia or Cryptosporidium parasites) in water treatment plant effluent and subsequently in water bodies (Semenza and Menne, 2009). Low flows and higher water temperatures also favour cyanobacterial and harmful algal blooms  (Mosley, 2015; Coffey et al., 2019). Dry periods boost recreational water activities, heightening exposure to pathogens like Leptospirosa spp., toxin-producing E. coli, enterococci, or parasites causing cercarial dermatitis (so-called swimmer’s itch).

High water and air temperatures

Vibrio

Elevated water temperatures accelerate the growth rate of waterborne pathogens, which pose human health risks through drinking water and recreational water use. Infections associated with marine environments are dominated by infections with Vibrio spp.[1], which thrive in warm water (>15°C) and low to moderate salinity. Warming of the Baltic Sea is regarded as the main driver for the substantial increase in Vibrio spp. infections in recent decades. Like all five European seas, the Baltic Sea has warmed considerably since 1870, particularly over the last 30 years (EEA, 2024), and its shallow, low salinity and nutrient-rich waters make it particularly suitable for Vibrio spp. According to van Daalen et al. (2024), 18 countries showed suitable areas for Vibrio spp. in Europe in 2022, and the length of affected coastline in these countries (23,011 km in 2022) shows a consistent increase between 1982 and 2022, particularly in western Europe. In various European countries, more Vibrio infection cases have been reported in years with summer heatwaves and exceptionally high temperatures (e.g., Folkhälsomyndigheten, 2023, Brehm et al., 2021). The risk of infection with the less common Shewanella spp. is also increasing with rising seawater temperatures in Europe (e.g. Naseer et al., 2019; Hounmanou et al., 2023).

Cyanobacteria

The primary factor influencing the presence of cyanobacterial blooms is nutrient availability, mainly nitrogen and phosphorus coming from agricultural fields with run-off. To a lesser extent, increased water temperatures can affect the occurrence of harmful cyanobacterial blooms, which peak in August (West et al., 2021; Huisman et al., 2018). Higher temperatures and low flows cause stratification in the water, which further favours algal blooms in nutrient-rich water (Mosley, 2015; Richardson et al., 2018). Increasing water temperatures influence the presence and distribution of some toxin-producing cyanobacteria species of tropical origin in Europe, such as Cylindrospermopsis raciborskii. Lake surface water temperatures across Europe have been warming since the 1990s, at a rate of 0.33°C per decade (C3S, 2023).

Harmful algae

Observed trends in the proliferation of harmful algal blooms in marine waters can be linked in part to ocean warming, marine heatwaves and depletion of oxygen, next to strong non-climatic drivers such as increased riverine nutrients run-off and pollution. As a result, climate change may fuel the exacerbation of harmful algal blooms in response to eutrophication (Gobler, 2020). In the south of Europe, warming sea temperatures cause a proliferation of marine dinoflagellate algae and the phytotoxins they produce (Dickey and Plakas, 2010). The neurotoxins easily accumulate in European coastal shellfish in the English Channel and Atlantic coastal region of Brittany (Belin et al., 2021), and cause gastro-intestinal diseases, neurological disorders and acute toxicity when consumed by people (Etheridge, 2010). In addition, cases of seafood poisoning from locally caught fish due to ciguatoxins have been documented in the Canary Islands and Madeira.

High air temperatures can adversely affect food quality during transport, storage and handling more generally.

[1] Vibrio parahaemolyticus, V. vulnificus and V. cholerae are important pathogens for humans

Projected effects

Vibrio infections are expected to continue increasing in the Baltic Sea due to climate change. The sea surface temperature suitability for Vibrio in the North and Baltic Sea is predicted to increase the number of months in a year with warm enough seawater for the potential presence of human pathogenic Vibrio spp. (Wolf et al., 2021). According to EFSA et al. (2020), Vibrio spp. are the biological hazard to human health with the highest likelihood of being exacerbated under climate change and having almost the highest impact on human health.

Increased temperatures and more frequent and intense extreme events (such as floods and droughts) associated with climate change are also likely to increase the risk of other water- and foodborne diseases, caused by viruses, bacteria and parasites.

Policy responses

Responses to prevent and reduce adverse health outcomes resulting from food- and waterborne diseases include establishment of effective surveillance systems of the diseases (especially during high-risk periods), strengthened food safety and water quality regulations and control, early warning systems and emergency plans, training and awareness raising among emergency, healthcare and public health professionals, information provision and awareness raising on risks and sanitary practices and counter-measures for the general public.

Monitoring of water- and foodborne diseases in Europe is done by ECDC and EFSA, based on data collected by EU Member States. ECDC produces annual epidemiological reports for notifiable diseases and updates the Surveillance Atlas of Infectious Diseases. It also produces risk assessments as needed in the event of outbreaks and rapid outbreak assessments with EFSA for foodborne outbreaks. EFSA produces, with the ECDC, annual summary reports on zoonotic infections and foodborne outbreaks.

The EU Drinking Water Directive requires that microcystin-LR, a common and widespread cyanotoxin, is measured when a cyanobacterial bloom is detected in a drinking water reservoir (EU, 2020b). The EU Bathing Water Directive states that in the event of potential blooms (increasing cyanobacterial cell density or bloom-forming potential), appropriate monitoring is to be carried out to enable timely identification of health risks. When cyanobacterial proliferation occurs and a health risk has been identified or presumed, adequate management measures must be taken immediately to prevent exposure, including providing information to the public.

Among the EEA member and cooperating countries, 24 have ratified the Protocol on Water and Health, an international, legally binding agreement for countries in the pan-European region to protect human health and well-being through sustainable water management and by preventing and controlling water-related diseases. Increasing resilience to climate change is one of the technical areas under the protocol’s programme of work (UNECE, 2022). 

Further information

References

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