Viral Pollution of Bottled Mineral Waters

Viral Nucleic Acid Analysis by Reverse Transcriptase-Polymerase Chain Reaction Highly Sensitive and Selective Tool for Pollution Monitoring

Mineral water is marketed for its healthfulness and purity.  However Swiss scientists now claim that some brands may contain human fecal contamination and human-derived pathogenic viruses.

Eleven of 29 European brands of bottled mineral water that Christian Beuret and his colleagues of the Cantonal Food Laboratory in Solothurn tested were found with signs of the virus that causes more than 90% of the world's stomach upsets1,2. The pollution marker 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," says Beuret. "We think human feces are sporadically contaminating the water either at the source or some time during the bottling procedure."

At present, the scientists do not know how this is happening or whether or not the water poses a health risk, as the samples cannot be tested for human infectivity.  Unpublished evidence has suggested that low levels of the virus in mineral water may give some elderly people gastroenteritis.

The findings are surprising but raise real arguments and concerns regarding the presence of human fecal contamination of all bottled products made with water.  The current concensus is that you only need a very low level - in the range found - of active virus for infections to occur.  However, the results must be further repeated by others because the technique used, called RT-PCR, is prone to contamination itself.

A statement from a leading company that markets bottled water says: "The RT-PCR technique is not suited to the routine analysis of potentially very weakly contaminated water." It must also be pointed out that NLV was not detected when six laboratories, including Beuret's, analysed 300 bottles of five brands in another unpublished study. 

Stability of Viral Pollution

NLV's genome is made of single-stranded RNA, rather than double stranded DNA. In the mineral water Beuret's team detected RNA sequences commonly found in the feces of people infected with NLV.

After a year of storage, nine out of ten virus-containing bottles were still contaminated. This stability suggests that these RNA sequences are not bare nucleic acid, but protein-coated particles, such as structurally intact virus particles.  This is required for the virus to be infectious. 

NLV RNA has been observed in healthy people. Some strains may remain viable but latent in the body without causing disease.

Although it's not known 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.

  1. Beuret, C., Kohler, D. & Luthi, T.. "Norwalk-like Virus Sequences" detected by reverse transcription-polymerase chain reaction in mineral waters imported into or bottled in Switzerland. Journal of Food Protection, 63, 1576 - 1582, (2000).
  2. Beuret, C., Kohler, D., Baumgartner, A. & Luthi, T.M. Norwalk-like virus (NVL)-sequences in mineral waters: One year monitering of three brands. Applied and Environmental Microbiology, 68, 1925 - 1931, (2002).

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