Norovirus outbreaks in hospitals and other healthcare settings are usually a result of person-to-person spread. Foodborne norovirus outbreaks are more commonly associated with hospitality settings, but they can and have occurred in hospitals. One such outbreak occurred in Japan and involved over 100 cases.

Food safety in healthcare settings

Food safety is an important and yet sometimes forgotten issue in healthcare settings but not meeting safety requirements in this area is particularly dangerous.

Hospital patients, a group which often includes older adults, young children and immunocompromised or immunosuppressed individuals, are at a higher risk of developing foodborne illness because they are more likely to be affected by even a small number of pathogens. They are also more likely to suffer more severe consequences from foodborne disease. For norovirus infections, hospital patients are also more likely to become chronically infected and pose a risk of transmission to others.

The challenge of removing norovirus from foods

Enteric viruses, such as norovirus, are particularly problematic because they are more resistant to heat and to disinfection. They are also more resistant to the environmental factors, such as pH and osmotic pressure, by which bacteria can be controlled in the food industry. In addition, they do not alter the taste, smell, or appearance of foods, and contamination is not apparent as it would be with, for example, bacterial spoilage.

For environmental disinfection, sodium hypochlorite at a concentration of 5000ppm is recommended. However due to its toxicity, concentrations of no higher than 200ppm are permitted in the food industry. Norovirus can be destroyed in the cooking process, although there is a risk that a small number of particles may still remain if foods are not heated sufficiently. Technologies such as irradiation, hydrostatic pressure and cold atmospheric plasma have been investigated, although the evidence for their use is still lacking. Additionally, one study reported that neither manual washing nor the dishwasher were effective in inactivating murine norovirus (MNV, a surrogate often used instead of human norovirus) from dinnerware such as plates, glasses and cutlery. 

Foods associated with norovirus infections

Foods can become contaminated with norovirus at their source or during handling. Norovirus is most associated with seafood. Seafood, and oysters in particular, have been associated with many norovirus outbreaks due to contaminated water. Similarly, fresh fruit and vegetables can be contaminated in the field from water and fertilisers. These usually include leafy vegetables such as lettuce and soft fruit such as strawberries and blueberries. These foods are usually eaten raw and the options for inactivating the virus are limited. In this type of contamination, different strains are often present in the food and it is quite common for cases involved in these foodborne outbreaks to be infected with mixed genotypes. 

Even more common is food becoming contaminated due to the poor food and personal hygiene of the handlers. Many foods responsible for causing norovirus outbreaks have become contaminated after preparation, shortly before serving. This could be directly from the hands of the infected food handler, from the food contact surfaces or from droplets of vomitus and faeces in the air following a recent contamination incident. Some of these types of outbreak were due to food handlers working while symptomatic, but pre-symptomatic, asymptomatic and post-symptomatic transmission has also been documented. For this type of contamination, all foods are potentially a risk. Foods implicated in this type of outbreak in healthcare facilities have included sandwiches, salads, and sausages. In other settings, bakery products and a variety of cooked products along with fresh fruit and vegetables were frequently found contaminated. Additionally, food handlers are not necessarily limited to those working in the kitchen. In hospital and other healthcare settings, nurses, healthcare assistants, volunteers and visitors are also considered food handlers. Raising awareness and educating these groups of food handlers is especially important to prevent potential outbreaks.

Foodborne and waterborne norovirus outbreaks

The epidemic curve of norovirus infection due to a contaminated food or water source is usually different than that found in person-to-person spread. The outbreak usually starts with a sharp increase in cases, many of which occur less than 24 hours after exposure. Attack rates are usually high and involve up to a few hundred cases per outbreak. Depending on the setting and the interventions in place, the initial rise in cases may be followed by a second wave due to interpersonal and environmental spread but in foodborne outbreaks, secondary transmission does not always occur.

Summary

Foodborne norovirus outbreaks are rare in hospitals and healthcare settings but may still occur. Due to its nature, norovirus is difficult to detect and eliminate in food products, therefore care needs to be taken to protect vulnerable patients from this illness. We should be aware that there are some groups of people who are considered food handlers in healthcare settings, but may not necessarily receive training to prevent foodborne illness.

Nutrition and Hydration Week 2022 runs between 14-20 March 2022. Find information about events, initiatives, posters and more here: nutritionandhydrationweek.co.uk