People who swim, bathe or take part in water sports in the sea are substantially more likely to experience stomach bugs, ear aches and other types of illness than those who do not.
The large-scale research analysis was led by the University of Exeter Medical School in collaboration with Dr Andrew Singer from the Centre for Ecology & Hydrology. It is the first systematic review to examine the evidence on whether spending time in the sea is associated with increased risk of reporting a variety of ailments.
The results demonstrated that sea bathing doubled the odds of reporting general ear ailments, and the odds of reporting earache specifically rose by 77%. For gastrointestinal illnesses, the odds increased by 29%.
The paper, entitled ‘Is it safe to go back in the water? A systematic review and meta-analysis of the risk of acquiring infections from recreational exposure to seawater’ is published in the International Journal of Epidemiology.
Despite significant investment resulting in an improvement water quality in recent years, seawater is still polluted from sources including industrial waste, sewage and runoff from farmland.
The researchers whittled down more than 6,000 studies to 19 studies which met the strict criteria for inclusion in the meta-analysis, designed to establish robust research evidence. Many of the studies included recruited thousands of participants. The number of people analysed in total exceeded 120,000. All the studies were conducted in high-income countries since 1961. The studies looked at the links between sea bathing and the incidence of illness in countries including the US, UK, Australia, New Zealand, Denmark and Norway.
Dr Singer said, “This new understanding is important for members of the public to manage their own exposure risk, but also important for guiding policy in reducing the sources of these human pathogens so that the odds ratios reported in this paper begin to approach 1.0 (i.e., no higher risk of bathing than watching someone bathe). Although most people enjoy the coastal waters without incident, this study shows for the first time that there is a significant increase in the risk of ear and gut ailments in those who are exposed to bathing waters.”
The main source of human pathogens in coastal waters is from treated sewage effluent, which is chronically released throughout a catchment 24-7. However, large pulses of untreated sewage effluent regularly occur in some coastal and non-coastal regions because the sewage works is unable to cope with the volume of water that has entered the sewage system.
"Although most people enjoy the coastal waters without incident, this study shows for the first time that there is a significant increase in the risk of ear and gut ailments in those who are exposed to bathing waters.” Dr Andrew Singer, Centre for Ecology & Hydrology
Dr Singer said, “This release of untreated sewage during and following moderate to heavy rainfall is a hugely significant source of human pathogens and must represent a priority for mitigation—without which there is unlikely to be much progress in this area. Our work at the Centre for Ecology & Hydrology is helping to monitor and assess the risk of pathogens and, in particular antimicrobial resistance, that originates from sewage works within UK catchments.”
This chronic source of pathogens and resistance genes will represent a stable source of coastal pollution which is potentially contributing to the observed increased Odds Ratio reported in the paper.
Dr Will Gaze, of the University of Exeter Medical School, supervised the research. He said, “We don’t want to deter people from going into the sea, which has many health benefits such as improving physical fitness, wellbeing and connecting with nature. However, it is important that people are aware of the risks so they can make informed decisions. Although most people will recover from infections with no medical treatment, they can prove more serious for vulnerable people, such as the very old or very young, or those with pre-existing health conditions. We have come a long way in terms of cleaning up our waters, but our evidence shows there is still work to be done. We hope this research will contribute to further efforts to clean up our coastal waters.”
The study was funded by the European Regional Development Fund.
The authors are Anne Leonard, Andrew Singer, Obioha Ukoumunne, William Gaze, and Ruth Garside.