Norovirus has been found in berries and salad vegetables in the United Kingdom, according to a study.

Researchers discovered 5.3 percent of lettuce, 2.3 percent of fresh raspberry, and 3.6 percent of frozen raspberry samples were norovirus-positive.

The study, scheduled to publish in June 2019 in the journal Food Microbiology, is part of the Norovirus Attribution Study (NoVAS), a research project funded by the U.K. Food Standards Agency. It runs through the middle of next year.

Noroviruses is easily passed from person to person. It can also be picked up from the environment or through eating food contaminated at source or by infected food handlers. It causes an estimated 3 million cases of diarrhea and vomiting each year in the United Kingdom, where it is estimated to be the third most common cause of foodborne illness.

During a 13-month period, 1,152 samples of fresh produce sold at retail in the U.K. were analyzed to acquire data on contamination. Findings included:

  • Of 568 samples of lettuce, 30 were norovirus-positive. Most, 24 from 30, of the samples that were positive for norovirus were grown in the U.K. and 19 of 24 contained the norovirus GI genotype.
  • Seven of 310 samples of fresh raspberries were norovirus-positive. Six of these samples were imported, but no predominant genogroup, or any seasonality, was observed.
  • Ten of 274 samples of frozen raspberries were norovirus-positive. The country of origin of the positively-testing frozen raspberry samples was not identified in seven cases.

Researchers said the data adds to the limited amount of prevalence information on norovirus in fresh produce. They added findings raise the question of whether food safety management systems for foodborne viruses are being effectively implemented in these commodity supply chains.

Other work in the NoVAS project includes determining the prevalence of norovirus contamination of oysters, salad leaves, and soft berry fruits on retail sale; to assess whether or not the norovirus found is likely to be infectious; and to determine the prevalence of norovirus contamination in the catering environment.

Another study as part of the project found under-reporting of norovirus outbreaks and inconsistency of reporting between organizations.

To estimate the burden of norovirus from seafood including shellfish, researchers used a capture-recapture technique using datasets from three different organizations involved in collecting information on outbreaks.

The number of outbreaks related to seafood in England was estimated for 2004-2011. Combined estimates were more than three times as high (N = 360) as the individual count from the organization (N = 115) which captured more outbreaks than the other two agencies.

A one-year study published in the middle of 2018 was on a survey of oysters that involved collecting them from the point-of-sale to the consumer from March 2015 to 2016. A total of 630 samples, from five different European Union member states, were collected from 21 regions across the United Kingdom.

Norovirus RNA was detected in more than two-thirds of samples, 68.7 percent, with strong winter seasonality. Those originating in the Netherlands showed lower prevalence and levels than those from the U.K. or Ireland.

Most samples, 76.5 percent, contained no detectable E. coli. However, in 2.4 percent levels above the statutory end product standard of 230 MPN/100 gram were detected.

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