Viruses Found in 40 Percent of European Recreational Waters

European researchers have found viruses in nearly 40 percent of more than 1,400 recreational water samples gathered from coastal and inland areas in nine countries, including Spain. The concentrations found are low but the scientists are calling for the monitoring of these microorganisms in recreational waters, especially after heavy rains when their populations skyrocket.

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) analyzed the presence of adenoviruses (viruses with DNA) and noroviruses (which have RNA and cause gastroenteritis) in 1,410 samples of both freshwater and seawater bathing areas 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 percent of the total), most of which were adenoviruses (in 36.4 percent of the samples compared with just 9.4 percent 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".
"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 wastewater 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 standardized (quantitative PCR) for detecting and quantifying viruses in bathing waters, which makes it possible to estimate the fecal 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 (excreted all year long in every geographical area and are found in 100 percent of wastewater samples) as an indicator of viral water contamination. The Catalan laboratory is one of the promoters of this initiative in Europe.