Viruses bathe in rivers and at the beach, too, European study finds

The European Bathing Water Directive establishes maximum levels for bacteria, in particular Escherichia coli and intestinal enterococcus, which must not be exceeded in order to maintain water quality. For viruses, however, the regulation only suggests that scientific studies should be carried out to help determine reference parameters and reliable detection methods.

Against this backdrop, 16 research groups from the Virobathe project, which is financed by EU funds, analysed the presence of adenoviruses (viruses with DNA) and noroviruses (which have RNA and cause gastroenteritis) in 1,410 samples of swimming water, both freshwater and seawater, in nine European countries. In Spain, for example, scientists from the University of Barcelona (UB) focused on the beaches at Gavà.

The overall results showed that 553 samples contained viruses (39.2% of the total), above all adenoviruses (in 36.4% of the samples, compared with just 9.4% for noroviruses), and more were found in freshwater than saltwater. A small selection of samples also showed that a quarter of the microorganisms had infectious capacity.

Adenoviruses are associated with gastroenteritis in children, some respiratory infections, ear infections and conjunctivitis, although a large part of the population has already been in contact with them and so is resistant to infection by most of the strains.

The study, which has been published in the journal Water Research, says that the presence of infectious adenoviruses and noroviruses in water samples "could pose a risk to health."

More microorganisms after storms

"In general, adenoviruses do not necessarily pose a significant risk to the population (if they are common strains that have already infected most people in childhood and if they remain at low levels). However, we know that virus numbers in bathing waters increase following heavy rains, meaning they could end up reaching dangerous levels," says Rosina Girones, director of the UB's Laboratory of Water and Food Viral Pollution and co-author of the study.

Viruses take longer than bacteria -- which are used as standard indicators -- to return to acceptable levels following heavy rains. In addition, many virus communities survive waste water treatment processes better than bacteria, and are more resistant to seawater.

The researcher highlights the importance of this study: "It shows that we already have a reliable technique that can be easily standardised (quantitative PCR) for detecting and quantifying viruses in bathing waters, which makes it possible to estimate the faecal contamination and quality of water. Aside from this there is no clear correlation between the levels of bacterial indicators cited in the regulation and the presence of the viruses studied."

The data obtained also lend support to the idea of using measurements of human adenoviruses, which are excreted all year long in every geographical area, and are found in 100% of waste water samples, as an indicator of viral water contamination. The Catalan laboratory is one of the promoters of this initiative in Europe.

The Spanish group is currently also participating in the international Viroclime project with four other EU countries and Brazil, in order to analyse the impact of climate change on the dispersal of pathogenic viruses in rivers, lakes and at beaches.