People who bathe in water in areas of Europe where birds have been tested positive for highly pathogenic avian influenza H5N1 are at negligible risk of infection with that virus, according to a risk assessment carried out by experts coordinated by the European Centre for Disease Prevention and Control (ECDC) to be published this week [1,2].

Some wild birds infected with H5N1 have been found in Europe, and these have mostly been waterfowl such as swans. Each year, especially in summer, thousands of people in Europe bathe in the sea, rivers and lakes. There has been concern about the safety of water which could be contaminated by faeces containing H5N1 from infected waterfowl.

However, the currently circulating H5N1 virus is poorly adapted to humans and exposure to large quantities of the current virus strain is thought to be necessary for transmission to a human. If infected birds have defecated into bathing or drinking water, the ECDC panel concluded that the dilution would be too great for there to be an infection risk.

For drinking water, normal water treatment processes would also destroy the virus. Even private untreated water supplies, such as wells, are not thought to be risky because of the great dilution and likely low infectivity of the H5N1 virus.

However, if convincing evidence should emerge that H5N1 has become better adapted to humans, this risk assessment would be reviewed and a more precautionary approach could be taken. Additionally, more caution might be required in a scenario where very high numbers of dead birds were found near a body of water.

Greater risk to humans from other waterborne pathogens
However, people everywhere are at risk of other infections, such as salmonellosis and campylobacteriosis, if they bathe in water which is contaminated. The scientific panel concluded that the safest areas to bathe in Europe were those where the water is regularly tested and meets the standards laid down in the recently updated European Bathing Water Safety Directive [3].