Case Studies in Food Safety and Authenticity

Lessons from Real-Life Situations

Jeffrey Hoorfar

• Publisher: Woodhead Publishing
• Year: 2012
• Print ISBN: 9780857094124
• eBook ISBN: 9780857096937
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

The identification and control of food contaminants rely on careful investigation and implementation of appropriate management strategies. Using a wide range of real-life examples, Case studies in food safety and authenticity provides a vital insight into the practical application of strategies for control and prevention.Part one provides examples of recent outbreak investigations from a wide range of experts around the world, including lessons learnt, before part two goes on to explore examples of how the source was traced and the implications for the food chain. Methods of crisis management are the focus of part three, whilst part four provides studies of farm-level interventions and the tracking of contaminants before they enter the food chain. Part five is focussed on safe food production, and considers the challenges of regulatory testing and certification, hygiene control and predictive microbiology. The book concludes in part six with an examination of issues related to food adulteration and authenticity.With its distinguished editor and international team of expert contributors, Case studies in food safety and authenticity is a key reference work for those involved in food production, including quality control, laboratory and risk managers, food engineers, and anyone involved in researching and teaching food safety.- Delivers a vital insight into the practical application of strategies for control and prevention of food contaminants- Provides detailed examples of recent outbreak investigations from a wide range of international experts, discussing how the source was traced and the implications for the food chain- Chapters discuss methods of crisis management, farm-level interventions, safe food production and the challenges of regulatory testing and certification

Part I

Outbreak investigations

1

Tracing an outbreak of listeriosis in Austria: what an investigative microbiologist needs to consider

D. Schoder, Institute of Milk Hygiene and Food Science, Austria

M. Wagner, Austrian Agency for Health and Food Safety, Austria

F. Allerberger, Christian-Doppler Laboratory for Molecular Food Analytics, Austria

Abstract:

An unusual cluster of three cases of human listeriosis occurred in Austria in the summer of 2009. As the months went by, the number of cases went up but no common source was initially identified. The outbreak seemed to be over, but then a second peak occurred. Since most of the cases occurred in elderly males, food typically consumed by males rather than females was suspected to have been involved. Then a bright idea came into play: could assessment of purchase behaviour help to identify the contaminated food commodity?

Key words

outbreak

listeria monocytogenes

epidemiology

tracking

1.1 Introduction to the case

On 14 August 2009 the Austrian Reference Centre for Listeria in Vienna first noticed the occurrence of a new pulsed-field gel electrophoresis (PFGE) pattern (clone 1) that was shared in human isolates of Listeria monocytogenes serotype 1/2a. Most cases occurred in elderly males. In the first outbreak phase, 14 clinical cases (12 Austrians and two Germans) infected with this new clone 1, including five with fatal outcome (two of them German), were identified, with onset of the disease ranging from June 2009 to January 2010 (Fretz et al, 2010a).

1.2 Significance of the case

Listeriosis is a rare but serious infection caused by Listeria (L.) monocytogenes. This organism can be found throughout the environment: in soil, vegetation, and animals. The main route of transmission is known to be through consumption of contaminated food. However, infection can also (in very rare cases) be transmitted directly from infected animals to humans. In neonatal infections, L. monocytogenes can be transmitted from mother to child in utero or during passage through the infected birth canal. The bacterium is particularly successful in causing foodborne disease, because it survives food processing technologies that rely on acidic or salty conditions, and, unlike many other pathogens, can continue to multiply slowly at low temperatures, allowing growth even in properly refrigerated foods (Allerberger and Wagner, 2010).

1.2.1 Regulatory aspects

Food contamination with L. monocytogenes is intensively regulated by international and national authorities. L. monocytogenes is prominent in Annex A of the EU ‘Zoonoses’ Directive 99/2003 and thus must be monitored in all member states. To harmonize microbiological food safety criteria, L. monocytogenes was promptly listed in the EU Directive 2073/2005. At a glance, the regulation states that L. monocytogenes must be absent from foodstuffs that facilitate the growth of the organisms, but it can be present up to a limit of 100 CFU/g if the physico- chemical profile of a food commodity prevents growth (the bacteria must not exceed 100 CFU/g food at the end of shelf-life; Anonymous, 2006). Since listeriosis is usually caused by a higher number of L. monocytogenes (> 10⁵ CFU/g), the search began for a food item that fosters growth and that is predominantly eaten by elderly persons.

1.2.2 Economic and market aspects

L. monocytogenes infections have the third highest mortality rate of all foodborne infections in the USA (Scallan et al. 2011). The pathogen is a contaminant of multiple food chains, including meat, dairy, fish, seafood and plant foods. However, from our own investigations we knew that three food categories contribute to the major burden of cases of contamination in Austria: smoked fish products, soft cheeses and cooked sausages (Wagner et al., 2007).

1.3 The case history continues

1.3.1 What made outbreak investigations difficult?

Since the incubation period of listeriosis in humans can be up to 70 days, the outbreak pattern is quite scattered, and thus a source of infection often remains undetected. Furthermore, due to the prolonged incubation period, foodstuffs have usually been eaten or already thrown away before an outbreak investigation starts. Due to the complexity of most outbreak scenarios, no pre-specified formulae dictate the path that an outbreak investigation is supposed to take.

1.3.2 What fostered the search for the source?

We collected grocery receipts of purchases made by seven patients in December 2009, after their discharge from hospital, and screened them for a common food item. The survey of the purchase behaviour allowed us to generate a hypothesis that was then tested by a case–control study using case-case comparisons. For this study, a case was defined as a person in Austria from whom the L. monocytogenes outbreak clone 1 was isolated (case group). Controls were patients from Austria with L. monocytogenes infections in 2009, whose isolates showed typing profiles other than the outbreak clone 1 (control group). Patients were asked about consumption of 12 cheese products in the six-month period prior to disease onset. Persons in the control group were requested to provide information on consumption of the same products and a parameter called the ‘odds ratio’ was computed (Fretz et al., 2010b).

1.4 Resolution and outcomes

1.4.1 Clinical dynamics

In total, the outbreak involved 34 cases of invasive listeriosis: 25 outbreak cases originated from seven of nine Austrian provinces. Another eight patients were from four German federal states, and one patient was from the Czech Republic. Eight of the 34 cases in this outbreak had a fatal outcome. The median age of the cases was 72 years (range: 57–89 years), and 26 patients were male (Fretz et al., 2010b). There were no materno-neonatal cases. Prevalence of underlying disease in the case group was not different from the prevalence of underlying disease in the control group.

1.4.2 Epidemiology did the job

In the case and control groups, 10 and 24 out of 12 and 33 possible cases (response rates: 83.3% and 72.2%), respectively, provided answers to the questionnaire. Consumption of Quargel cheese was identified as the only significant risk factor highly associated with the illness in question. Nine of the ten patients with clone 1 had consumed the product; the tenth provided no answer concerning this food item. Of 22 controls all but two denied having eaten this specific cheese; the remaining two provided no answer concerning this food item. The computed odds ratio was 76.6 (95% confidence interval (CI): 9.3–infinity; p-value < 0.001).

Interestingly, molecular typing revealed that two clones of the same serovar 1/2a of L. monocytogenes had contributed to the outbreak. Whereas the first clone caused 14 cases in the first phase of the outbreak (Summer–Autumn 2009), the second outbreak clone accounted for 20 cases (13 Austrian cases, six German cases, one Czech case) that were reported from December 2009 until the end of February 2010 (Fig. 1.1).

Fig. 1.1 Outbreak cases of listeriosis by onset of illness and final outcome, Austria, Germany and the Czech Republic, 2009–2010. n = 34; Austria = 25, Germany = 8, Czech Republic = 1.

1.4.3 Short description of Quargel processing technology

This cheese is made of curdled milk which ripens, after addition of starter cultures, for one day at 28 °C, and for another two days at 14 °C by spraying the surface with Brevibacterium linens. The shelf life after packing is up to 50 days. With regard to the incriminated plant, 16 tons of Quargel cheese were produced per week. Almost 50% of the cheese was exported to the German market and small amounts to the Czech Republic and Slovakia.

1.4.4 Contamination rates of samples and recalled lots of Quargel

Only one leftover specimen, stored in the patient’s refrigerator and sampled on March 3rd, could be tested by the public health authorities and yielded 2 100 000 CFU/g of L. monocytogenes. Despite the high profile of the topic in the mass media, the patient and his wife were not aware of the product recall.

Two of 64 isolates available for testing (44 isolates cultured from cheese produced in 2010 and provided by the manufacturer, 20 isolates cultured from samples officially obtaine...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Obituary for Niels Skovgaard
• Contributor contact details
• Woodhead Publishing Series in Food Science, Technology and Nutrition
• Preface
• Foreword
• How to use this book
• Acknowledgements
• Part I: Outbreak investigations
• Part II: Source tracing
• Part III: Crisis management
• Part IV: Farm-level interventions
• Part V: Safe food production
• Part VI: Food adulteration and authenticity
• Index