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Q Fever Risk to Human Health from the Consumption of Contaminated, Unpasteurised Milk and Milk Products


<p>The original proposal to the FSA specified a full farm-to-consumption quantitative microbiological risk assessment to assess the risk to humans from the consumption of unpasteurised milk and milk products made from unpasteurised milk of UK cattle, sheep and goat origin. The risk assessment was to follow the main steps of the Codex risk assessment framework (CAC, 1999), which is most commonly used for food safety risk assessments. Using the Codex framework, a risk assessment is split into the following components; Hazard identification, exposure assessment, hazard characterisation and risk characterisation. However, during the hazard identification stage of the risk assessment it became clear that there were significant data gaps in the level of knowledge of C. burnetii. In particular there was little or no information on:</p>

<li>levels and viability of C. burnetii in sheep and goats' milk</li>
<li>survival of C. burnetii in unpasteurised milk and milk products</li>
<li>survival and fate of C. burnetii during the cheese-making processes and manufacture of other milk products</li>
<li>dose-response data for humans through the oral route</li>
<li>current farm prevalence and within herd/flock prevalence of C. burnetii (ELISA and PCR data are available but will overestimate the prevalence); and</li>
<li>Qualitative or quantitative studies on consumption patterns of unpasteurised milk and milk products</li>

<p>Those data gaps in part reflect the difficulties in routine culture of C. burnetii and also the lack of data on the viability of the organisms when DNA is detected by PCR methods. It was therefore agreed that an alternative approach was required as there were insufficient data for a full quantitative or qualitative risk assessment. Overall, the revised work programme included four deliverables:</p>

<li>the hazard identification</li>
<li>the development of a risk profile for C. burnetii through consumption of unpasteurised milk and milk products</li>
<li>the identification of the risk pathways to humans through consumption of unpasteurised milk and unpasteurised cheeses; and</li>
<li>the development of an exposure assessment model, together with a sensitivity analysis, for humans consuming unpasteurised cows' milk</li>

<p>Of additional interest was the risk to humans due to consumption of unpasteurised milk/milk products during an abortion storm* at a goat farm. In the absence of sufficient data for goats, a scenario analysis was undertaken for cows' milk to represent an outbreak within a cattle herd. The risk assessment was reviewed by the Advisory Committee on the Microbiological Safety of Food (ACMSF meeting of 27/6/13). See: ACMSF website</p>

<p>*A large number of abortions typically caused by infectious disease</p>

More information

<p>Background: Q fever is a widespread zoonotic disease caused by the bacterium Coxiella burnetii and is present in cattle, sheep and goats. In most cases clinical illness is not seen, but occasional large outbreaks or clinical cases of Q fever are reported in animals. The clinical manifestations of Q fever in humans are variable, ranging from asymptomatic to serious. The main route of transmission to humans is via the inhalation of aerosols from the parturient (birth) products of infected animals. It is known that meat, milk and milk products can be contaminated. However, the link to clinical disease in humans is unclear.</p>

<p>The original aim of this work was to undertake a quantitative risk assessment for C. burnetii in unpasteurised milk and milk products from UK cattle, goats and sheep. However, in part due to the problems in culturing this pathogen, much of the data required for the risk assessment are missing. It was therefore agreed with the Food Standards Agency to develop a risk profile for C. burnetii through unpasteurised milk and milk products and, instead of developing a full risk assessment, to conduct an exposure assessment for consumption of unpasteurised cows’ milk.</p>

<p>This will allow the FSA to make consistent, evidence-based risk management decisions in relation to Q fever risks from unpasteurised milk and milk products. </p>

Animal Health and Veterinary Laboratories Agency (AHVLA)
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