The European Food Safety Authority (EFSA) asked the Panel on Biological Hazards to initiate a self tasking issue with the purpose to provide up-to-date information on the present knowledge on the occurrence and control of foodborne viruses. The BIOHAZ Panel carried out a review of the available information in the scientific literature with regards to the biology, epidemiology, diagnosis and public health importance of foodborne viruses. Where possible the review covered primary production, food harvesting, food processing, and storage/retail until consumption. Data needs to support a risk assessment were also identified. In addition possible control options and their anticipated impact to prevent or reduce the number of foodborne viral human infections were identified including the scientific reasons for and against the establishment of microbiological criteria for viruses for certain food categories (e.g. fresh produce, bivalve molluscs etc).
The opinion draws conclusions on the biology, epidemiology, diagnosis and public health importance of the foodborne viruses Norovirus (NoV), Hepatitis A virus (HAV) and Hepatitis E virus (HEV).
NoV infection is the most common cause of infectious human gastro-enteritis. NoV is shed in huge quantities in the stool and vomit of infected persons, and oral exposure to only a few particles is sufficient to cause disease. HAV is the aetiological agent of the most common type of hepatitis worldwide. Infectivity is unknown but may be very high. In contrast to NoV and HAV, HEV has been identified also as a zoonosis. Although rare, its importance is increasingly recognised in the EU. The dose response relationship for HEV for humans, is unknown.
In the EU, the major mode of transmission for NoV remains person-to-person (directly from the human reservoir). In the EU, the major mode of transmission for HAV is directly or indirectly from the human reservoir, mainly as a consequence of travelling to endemic regions, having risky sexual practices or consuming contaminated water or food.
Food may be contaminated by virus during all stages of the food supply chain, and transmission can occur by consumption of food contaminated during the production process (primary production, or during further processing), or contaminated by infected food handlers. Transmission of zoonotic viruses (e.g. HEV) can also occur by consumption of products of animal origin, although few cases are reported. Viruses do not multiply in foods, but may persist for extended periods of time as infectious particles in the environment, or in foods.
At the EU-level it is unknown how much disease caused by NoV can be attributed to foodborne spread. Studies in some countries suggest that this can be significant. The relative contribution of different sources (shellfish, fresh produce, food handler including asymptomatic shedders, food handling environment) to foodborne illness has not been determined. Current EU surveillance for foodborne NoV illness does not capture dispersed outbreaks very efficiently, and there is clear evidence of significant underreporting of foodborne NoV outbreaks. The background data from case reports of HAV is often insufficient to prove foodborne transmission, but occasional outbreaks have been documented. With the decreasing immunity to HAV in the EU population, the probability of outbreaks is increasing. The diagnosis of HEV infections in humans is not routinely done in most laboratories, and therefore, there is considerable under diagnosis of this infection and illness.
Possible control options and their anticipated impact to prevent or reduce the number of foodborne viral human infections are given in the opinion together with several recommendations.
Thus, it is recommended to focus on preventive measures to avoid viral contamination rather than trying to remove/inactivate these viruses from food. Also it is recommended to introduce microbiological criteria for viruses in bivalve molluscs, unless they are labelled “to be cooked before consumption”. These criteria could be used by Food business operators to validate their control options to meet the established virus criteria. Using an E. coli standard for monitoring and classification of bivalve mollusc production areas provides general information about the background level of faecal contamination, and is recommended to be retained.
Furthermore the regulatory standards and monitoring approaches could be refined to improve public health protection. Introduction of virus microbiological criteria for classification of high risk bivalve molluscs (to be consumed raw) production areas should be considered. A virus monitoring programme for compliance with these criteria should be risk based according to the findings of a sanitary survey.
It is also recommended that EU environmental legislation considers specific protection against faecal pollution to bivalve mollusc production areas. Control measures need to focus on avoiding faecal contamination in mollusc production areas as much as possible. Sanitary surveys would provide the necessary knowledge base. Preventative approaches could include: introduction of prohibition zones in the proximity of sewage discharges, more stringent E. coli standards for class B classification areas, and the use of pollution alert procedures.
Post-harvest treatments need to be validated for virucidal activity (e.g. using HAV as a model) to ensure that the treatments are effective, and can be applied consistently prior to implementation in the food production chain. In addition further training of food handlers about hygiene requirements and about specific viral contamination of foods and food preparation environment is recommended in order to reduce the risk of contamination of ready-to eat foods. Finally it is recommended that high risk groups (people with underlying liver disease, immuno-compromised persons and pregnant women) should be discouraged from eating meat and liver derived from wild boars and domestic pigs without proper cooking for prevention of hepatitis E.
In the opinion data needs to support a risk assessment have also been identified. Thus routine harmonised surveillance of NoV, and of virus occurrence in food commodities including molecular typing is recommended to aid source attribution studies. For HEV and HAV, notification and systematic strain typing of viruses in humans and in animals (HEV) and food commodities (HAV) are needed to get a better understanding of sources of virus. Studies are also needed to determine the importance of foodborne transmission pathways for HEV.
To determine the burden of disease, including foodborne illness, population-level estimates of incidence, risk factors, and clinical impact of NoV, HAV, and HEV in humans in general, and in specific risk groups (e.g. immuno-compromised individuals, elderly) are needed. Studies are also needed to determine the importance of presymptomatic, postsymptomatic, and asymptomatic shedding of NoV and HAV as sources of foodborne human infection.
In order to quantify the efficacy of specific control options, it is necessary to build a quantitative risk assessment framework. This should be done for specific priority virus-commodity combinations, including consideration of the target population. Data needs for QMRA of FBV include: consumer habits, virus contamination levels in food and other reservoirs, virus transfer rates, natural persistence on/in foods (at the pre-harvest and post-harvest levels), and human dose-response relations. These data should be collected based on specific targeted studies, including sampling strategies. In addition, more studies are needed on the relation between detection of virus genomic copies by PCR in food and probability of causing disease. For this purpose, a guidance for outbreak investigation for FBV-related outbreaks could be drawn up to generate the type of data needed for QMRA.