Norwalk-like virus sequences detected by reverse transcription-polymerase chain reaction in mineral waters imported into or bottled in Switzerland

Norwalk-like viruses (NLVs) is a genus belonging to the Caliciviridae. NLVs are transmitted by the fecal-oral and the aerosol route and are the most common cause of outbreaks of nonbacterial gastroenteritis. NLVs are responsible for an estimated 67% of all illnesses caused by known foodborne pathogens and for 96% of nonbacterial gastroenteritis in the United States. Many outbreaks could be associated with the consumption of primarily or secondarily contaminated foods. To our knowledge, no epidemic arising from contaminated mineral water has been reported. We investigated the presence of NLV sequences in 63 mineral waters of 29 different brands that were imported into or bottled in Switzerland. NLV sequences were detected in 21 mineral waters by reverse transcription-seminested polymerase chain reaction. Specimens of two NLV genogroups (gg), gg I and gg II, were randomly present in the contaminated samples. The presence of NLV sequences could not be correlated either with bottle characteristics or with chemical properties like mineralization, pH, or the presence of carbonic acid. Nucleotide sequence analysis of 12 NLV-positive samples revealed several point mutations. All isolated NLV gg I strains have a similarity of 70 to 87% with the common Desert Shield virus (UO4469), and all isolated NLV gg II strains have a similarity of 89 to 93% with the Camberwell virus (U46500). Possible reasons for the presence of NLV sequences in mineral waters are discussed.