Amidst heatwave across Europe, ECDC launches improved tool for monitoring the risk of infection in coastal waters

Vibrio bacteria occur naturally in coastal waters, especially where it is warm and there is a mixture of salt and fresh water. People can become infected if contaminated water enters a cut or wound, or if they eat raw or undercooked seafood and shellfish (such as oysters) contaminated with the bacteria. While infections remain relatively rare in Europe, warmer water temperatures can increase the growth of Vibrio bacteria in coastal waters and thereby increase the risk of infection. 

The updated tool shows where environmental conditions are favourable for the growth of Vibrio bacteria, based on sea surface temperature and sea salt concentration data from European satellites. Developed more than 10 years ago, it provides daily risk estimates as well as a five-day forecast, helping to inform citizens when and where they need to be cautious when bathing. It can also alert bathers and medical staff to watch for symptoms that may indicate vibriosis. 

The areas of heightened risk depend on the weather and particularly the temperature, making early warning and prevention all the more important. After the recent heat wave in Central Europe, the risk rose quickly to unusually high levels for so early in the season. Last year, in contrast, there was a heatwave in northern Sweden, Norway and Finland with temperatures of 30 degrees for almost a month at a time, when the northern stretch of the Baltic Sea unusually became a risk area for Vibrio.

In Europe, the Black Sea, Baltic Sea and parts of the North Sea, where the salt levels remain favourable for Vibrio, are the main risk areas when water temperatures rise. However, estuaries, where rivers meet the sea and the water is normally more salty, can also be suitable for Vibrio to flourish.

Vibriosis symptoms can vary. Eating raw or undercooked shellfish typically causes diarrhoea, abdominal pain, nausea, vomiting, fever and chills. Exposure to Vibrio bacteria in water can lead to infected wounds or ear infections, causing redness, swelling and pain. Without treatment, these may worsen, leading to severe complications.

ECDC also monitors the likelihood of Vibrio bacteria in coastal waters on a weekly basis and publishes updates on high-risk areas in its Weekly Communicable Disease Threat Report throughout the summer season.