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<p>This study aimed to develop an initial system dynamics model to help inform the FSA's strategy in tackling norovirus by:</p>
<ul>
<li>developing a better understanding of the relative contributions of the food-related routes of transmission of norovirus</li>
<li>assessing whether reducing risks in the food chain will have a material effect on the number of human cases, given the high level of person to person spread</li>
<li>identifying gaps where further research may be required</li>
</ul>
<p>The main routes of transmission included in the model are person to person, infected food handlers, bivalve shellfish and produce such as berry fruit and leafy vegetables.</p>
<p>The project followed six main stages:</p>
<ul>
<li>interviews with a number of norovirus experts to conceptualise the model and obtain an initial understanding of parameter values.</li>
<li>creation of a first-cut model based on information gathered in the interviews.</li>
<li>additional expert consultations, as necessary, to obtain further parameter values.</li>
<li>completion of model formulation and parameterisation.</li>
<li>model analysis - extraction of indicative findings on relative importance that food plays in norovirus transmission; identification of gaps in knowledge about parameter values; recommendations for further work.</li>
<li>creation of a report on modelling work and summary presentation of study.</li>
</ul>
<p>The model has been transferred to the FSA's Operational Research Unit for further in-house development as necessary.</p>
<p>Background: Norovirus is one of the major sources of Infectious Intestinal Disease (IID) in the UK with about 2.8 million estimated cases in 2009. Like many enteric viruses, there are a number of different routes of infection that are thought to be significant in the spread of norovirus, which is easily passed from person to person. Other routes include contaminated foods, such as shellfish and fresh produce and infected food handlers.</p>
<p>The relative importance of these different routes for norovirus transmission is not well understood, nor is the way in which they interact with each other. This makes it difficult to target efforts on developing effective interventions that will reduce the number of cases. In particular, the relative importance of infection from contaminated food is uncertain, particularly given the frequent occurrence of transmission from person to person. Understanding this will help inform whether interventions directed at the food chain are likely to have significant impacts on reducing overall numbers of cases of norovirus.</p>