Swiss scientists say that some brands of mineral water may be contaminated with human faeces.
In 11 of 29 European brands of bottled mineral water, Christian Beuret and his colleagues at the cantonal food laboratory in Solothurn found signs of the virus that causes more than 90% of the world's stomach disorders. The virus is called Norwalk-like virus or NLV.
"We didn't believe the results at first, so we got them independently confirmed by a private Swiss lab," Beuret told Nature Science Update, the online news service of the science journal, Nature.
"We think human faeces are sporadically contaminating the water either at the source or some time during the bottling procedure." The team does not yet know how this might be occurring.
It is also not known whether the water poses a health risk though evidence suggests that low levels of the virus in mineral water may give some elderly people gastroenteritis.
The mineral water industry warned that the technique used by Beuret's team, called RT-PCR, is prone to contamination.
"The RT-PCR technique is not suited to the routine analysis of potentially very weakly contaminated water," a leading company that markets bottled water told Nature Science Update.
NLV's genome is made of single-stranded RNA. In the mineral water, Beuret's team detected RNA sequences, which are commonly found in the faeces of people infected with NLV.
After a year, nine out of ten virus-containing bottles were still contaminated. The length of time suggests that an envelope of proteins surrounds the virus protecting its RNA. These proteins also make the virus infectious.
Strains lie dormant
NLV RNA has been spotted in healthy people suggesting some strains may lie dormant in the body without causing disease.
Tamie Ando studies viral gastroenteritis at the national centre for infectious diseases in the United States.
"Although we don't know whether the strains found in the mineral water are dangerous, the work is very important because we need to learn how our environment has been contaminated by these viruses," Ando told Nature Science Update.
The announcement follows two separate studies, published in different scientific journals.
Two years ago, in the Journal of Food Protection, Beuret's team looked at mineral waters imported into or bottled in Switzerland. The latest study published in Applied and Environmental Microbiology monitored three brands over a year.