B12001: Microbiological risk assessment for norovirus infection - contribution to the overall burden afforded by foodborne infections
Wednesday 27 July 2005
This research project assessed the feasibility of estimating the contribution of foodborne norovirus transmission to the overall burden of gastroenteritis caused by norovirus in the UK.
Background
Noroviruses (NV) are a highly infectious group of viruses and a significant cause of gastroenteritis epidemics in the United Kingdom and elsewhere. A considerable number of infections occur through norovirus transmission by contaminated food and person-to-person contact. However, significant data gaps make it difficult to assess the relative importance of the different norovirus transmission routes. Consequently, the significance of foodborne transmission to overall NV disease incidence is poorly understood.
This project therefore assessed the feasibility of conducting a quantitative microbiological risk assessment (QMRA) aimed at establishing the contribution made by the food chain to the total incidence of NV disease. Once the role of foodborne transmission to overall NV disease incidence is understood, public health interventions can be better focused towards tackling critical points in disease transmission, thereby reducing the number of cases of NV disease.
Results and findings
This project identified three transmission routes as being responsible for the greatest contribution to norovirus (NV) disease in the UK. These were:
- person-to-person NV transmission
- foodborne transmission via bivalve shellfish (mainly contaminated raw oysters)
- foodborne transmission via salads, fruit and vegetables (raw, ready-to-eat food group involving commercial food handlers)
The project developed a mathematical model of person-to-person NV transmission. This model is capable of assessing the potential impact that a reduction in foodborne NV transmissions would have on the incidence of NV disease in the general population.
As input, the model requires estimates of the NV disease incidence, as well as the rate of either person-to-person transmission or exogenous transmissions (that is, non person-to-person transmission routes, including the foodborne route). However, current estimates of these figures are too unreliable to allow an accurate assessment of the impact that a reduction in foodborne transmissions might have on overall NV disease incidence.
The risk modules and person-to-person transmission model made it possible to identify those data gaps that prevent a quantification of foodborne NV transmission routes. This enabled the project to recommend specific research areas where future work would significantly improve our knowledge of the relative burden of disease that arises from the different NV transmission routes. The project's recommendations for future work include:
- dietary surveys on raw and cooked oyster consumption, as well as point-of-sale surveys looking at the contamination of oysters with NV
- surveys of NV infections among catering staff and of staff's work practices during times of infection
- quantification of the number of cases generated per infected food handler through epidemiological studies of existing outbreak data
- studies to determine the relevance of asymptomatic shedding of virus
- estimation of the true community transmission rate excluding foodborne transmission by following chains of infection in the general population
This project has provided a thorough appraisal of the available data on NV. The development of models for the most important transmission routes will form a valuable basis for future research. The project also identified specific data and research requirements for the successful conduct of a full quantitative microbial risk assessment of foodborne NV transmission. The project's findings will be very valuable in informing the Agency's future research on foodborne NV transmission.
Dissemination information
Final report is available from the Agency's Information centre. The final report also includes an extensive annotated bibliography on NV transmission as well as a bibliographic database (Access) on CD-ROM which details all information sources used during the project.
To obtain a copy of the final report, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk).
Contact: For any enquiries concerning this research project, please contact the relevant programme contact or email science@foodstandards.gsi.gov.uk