FSA activity and research on norovirus

The FSA is focusing its activity and research on foodborne norovirus in three key areas. They are food handlers, shellfish and fresh produce.

Food handlers and norovirus transmission: Social science insights

FSA has published research carried out by Ipsos MORI, Food handlers and norovirus transmission: Social science insights. This study aimed to help stop the 'winter vomiting bug' norovirus from spreading, by understanding and improving food handler behaviours.

The literature review identified 5 strategies for controlling norovirus:

1. Personal hygiene
2. Food handling
3. Washing and cooking food
4. Surface and uniform cleaning
5. Fitness to work

Visits to food catering establishments involved in-depth interviews, surveys, and structured environmental and behavioural observations. Strongest evidence was found for:

• inadequate hand washing;
• not washing hands before gloving;
• using bare hands when preparing food;
• not regularly changing gloves;
• food handlers instead of trained staff cleaning areas where people vomited;
• not washing uniform correctly;
• and returning to work too early after being ill.

Data analysis and behavioural theories were used to rank behaviours which risk spreading Norovirus in relation to the control strategies, according to the strength of evidence that food handlers were expressing these behaviours.

Several behavioural interventions were recommended based on the findings. Just as one example: strong evidence indicated inadequate knowledge of how to stop Norovirus spreading, so educational training for food handlers was highly recommended. FSA is exploring the design and delivery of future interventions.

Food handlers

Foodborne disease, including norovirus, can occur if a person with an infection who prepares and serves food, whether in catering, food manufacture or in the home. Norovirus is highly infectious, this means the organism is likely to be easily spread by food handlers who:

  • have been symptomatic (have had diarrhoea and/or vomiting) and return to work while still shedding virus particles and fail to follow the relevant hygiene requirements
  • are asymptomatic (who are infected but show no symptoms), but are nonetheless shedding virus and fail to follow the relevant hygiene requirements
  • have an episode of diarrhoea or vomiting, which may have resulted in the spread of virus particles to food, surfaces or furnishings, in the workplace or the home

Norovirus illness can often start unexpectedly. This may result in sudden episodes of diarrhoea or vomiting and therefore a secondary spread of virus particles throughout a home, catering, retail or manufacturing environment is possible. Spread of infection can occur from this initial episode, or as a result of insufficient cleaning and disinfection of surfaces and subsequent cross contamination.

Shellfish

Raw or lightly cooked shellfish is a known way for norovirus to infect a person. Shellfish has been linked to a number of outbreaks and incidents in the UK and internationally. An FSA-funded study (research project number FS235003), published in November 2011, found that 76% of samples of pooled oysters analysed at harvest from UK harvesting areas over a two-year period tested positive for norovirus. This was detected at low levels in more than half of the positive samples (52%).

Oysters and other bivalve molluscs, such as mussels, filter large volumes of water to get their food and any pathogenic bacteria and viruses in the water can build up within the shellfish. Norovirus contamination in shellfish is most likely to have originated from treated or untreated sewage that may have been discharged into waterways and then accumulated by shellfish as they feed.

Controls after commercial harvesting, for example the depuration process, provide good protection against harmful bacteria such as E.coli, but are less effective in removing viruses from live shellfish.

Fresh Produce

Fresh produce, such as leafy green vegetables and berry fruits, is a known way for norovirus to spread. Outbreaks of norovirus linked to these produce types, particularly imported frozen berries, have been recorded within the European Union (EU) and elsewhere in the world. However, to date fresh produce has not been implicated in the UK.

There is potential for fresh produce to become contaminated with norovirus at various points in the production chain. These are:

  • use of contaminated water for agricultural or hygiene purposes, for example irrigation, washing produce, application of plant protection products
  • cross contamination from unclean on-farm harvesting equipment
  • cross contamination from pickers handling produce on-farm and in packing areas (particularly where good hygienic practices such as handwashing are not observed
  • cross contamination by handlers at retail

Risk assessment of production practices alongside stringent application of Good Agricultural Practices (GAP) is essential. These and other controls intend to prevent direct and indirect contamination of fresh produce from food handling and production practices. These practices are especially important where fresh produce will not be cooked prior to consumption.

In partnership with the Horticultural Development Company, the FSA has produced guidance to help UK fresh produce growers implement practical controls and risk assessment. This guidance can be found at the link below.

In addition, specific guidance on prevention of viral contamination for leafy greens and berry fruits has been developed as part of the EU-funded VITALproject which looked at integrated monitoring and control of foodborne viruses in European food supply chains.

Preventing contamination and infection

The most effective way to prevent transmission of norovirus, whether person-to-person or contamination of food, is through people practicing good personal hygiene, especially regular and effective handwashing. In addition, it is important that food handlers, whether in food production or catering settings, do not attend work while experiencing diarrhoea and vomiting and should not return to work unless symptoms have ceased for 48 hours. The same advice also applies for people in their own home to prevent the spread of infection within the household.

Advice on managing staff sickness can be found in the Food handlers: Fitness to work guidance. This guidance explains that:

  • diarrhoea and/or vomiting are the main symptoms of illnesses that can be spread through food
  • staff handling food or working in a food handling area must report these symptoms to management immediately
  • managers must exclude staff with these symptoms from working with or around open food, for 48 hours from when symptoms stop

In addition, all staff who handle food and who work around open food must always:

  • wash and dry their hands before handling food, or surfaces likely to come into contact with food, especially after going to the toilet, as it is possible to be infected but not have symptoms
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