Outbreak Investigation

Part A (20 marks)

Smith, AJ, McCarthy, N, Saldana, L, Ihekweazu, C, McPhedran, K, Adak, GK, Iturriza-Gomara, M, Bickler, G and O’Moore, E 2012, A large foodborne outbreak of norovirus in diners at a restaurant in England between January and February 2009, Epidemiology and Infection, vol. 140, pp. 1695-1701
https://www.proquest.com/docview/1030237269/shibboleth?accountid=14205 (Links to an external site.

1. The authors state that norovirus is the most commonly known cause of infectious intestinal disease in Western Europe and North America.

  1. What are some of the features of norovirus that makes it so common? (1 mark)
  2. Is norovirus a notifiable disease in Victoria? (1 mark)
  3. Do you think notification data could be used to accurately estimate the true prevalence of norovirus? (1 mark)
  4. What other data might be used to estimate the prevalence of norovirus?(1 mark)

2. What are the three key components of an outbreak investigation? Briefly describe how this study addressed these three components. (3 marks)

3. The authors stated that the delay in reporting the outbreak to the health authority impeded the investigation.

  1. What are some possible reasons why customers reported their illness to the restaurant rather than to the health authority? (1 mark)
  2. How did the delay impact on the interviews with affected diners? How did the investigators work around this?(1 mark)
  3. How did the delay impact on the food and environmental investigations? (1 mark)

4. An analytical study was undertaken to identify risk factors in order to make recommendations to assist in the prevention and control of future outbreaks.

  1. What type of analytical study was undertaken? (1 mark)
  2. What were the case and control definitions? (1 mark)
  3. Why is it important to establish a case definition when investigating an outbreak? (1 mark)
  4. Why were staff members also interviewed as part of the investigation? (1 mark)

5. The authors stated that the investigation of staff food handling and hygiene practices was undertaken by interview rather than observation. What are some limitations associated with this method of data collection? (1 mark)

6. Describe the shape of the epidemic curve. What did the epidemic curve reveal about the incubation period and type and magnitude of the outbreak? (1 mark)

7. The univariate analysis found that the oyster, passion fruit jelly, lavender dish had an odds ratio of 18.0. Explain how this was calculated and what it means. (1 mark)

8. Explain why molluscs are susceptible to norovirus contamination and why they are often implicated in foodborne disease. (1 mark)

9. Explain why food handlers likely contributed to this outbreak. (1 mark)

10. What were some of the measures that were suggested to prevent or control outbreaks of this nature in the future? (1 mark)

Part B (15 marks)

Read the article by de Gooyer et al. (2017) and answer the questions below.


de Gooyer, TE, Gregory, J, Easton, M, Stephens, N, Fearnley, E and Kirk, M 2017, Waterparks are high risk for cryptosporidiosis: a case-control study in Victoria, 2015, Communicable Diseases Intelligence, vol. 41, no. 2, pp. E143-E149
https://www1.health.gov.au/internet/main/publishing.nsf/Content/cda-cdi4102c.htm (Links to an external site.)Links to an external site.


1. The authors state that cryptosporidiosis is the third most commonly notified gastrointestinal disease in Australia.

  1. What was the prevalence of the disease in 2014 according to the article? (1 mark)
  2. Which notifiable disease group does cryptosporidiosis belong to according to the Public Health and Wellbeing Regulations 2009? (1 mark)

2. Cryptosporidiosis is a type of gastrointestinal illness.

  1. Describe the aetiological agent that causes cryptosporidiosis. (1 mark)
  2. What is the incubation period for the disease? (1 mark)
  3. What are the symptoms of cryptosporidiosis?(1 mark)

3. Explain why swimming pools are commonly implicated in outbreaks of cryptosporidiosis. (1 mark)

4. The authors state that the DHHS detected an increase in cryptosporidiosis in March and April 2015 in one particular region which prompted an epidemiological investigation.

  1. What was the aim of the case-control study?(1 mark)
  2. What were the case and control definitions? (1 mark)
  3. What risk factors were investigated using the telephone questionnaires and which risk factors were found to be significantly associated with illness?(1 mark)
  4. The epidemic curve revealed several peaks of onset. What did the authors suggest this meant? (1 mark)

5. An environmental investigation was undertaken as part of the study.

  1. What did the environmental investigation by local government environmental health staff reveal as a potential contributing factor to the outbreak? (1 mark)
  2. What actions were undertaken by the authorities and water park operators to control the outbreak? (1 mark)

6. What design factors associated with waterparks and toddler pools were identified as increasing the cryptosporidiosis risk of these pools? (1 mark)

7. Explain what the authors mean by “bi-modal age distribution of notification rates of cryptosporidiosis” and “notification bias”. (1 mark)

8. What are some reasons why a microbiological investigation of water from the implicated waterparks was not undertaken? (1 mark)

Part C (12 Marks)

Read the article by Kent, Gregory & Patel (2011) and answer the questions below.


Kent, L., Gregory, J., & Patel, M. 2011. Salmonellosis outbreak linked to the consumption of fried ice-cream. Victorian Infectious Diseases Bulletin, vol. 14, no. 4, pp. 114-117.

https://research.avondale.edu.au/nh_papers/87/Links to an external site.


1. Salmonellosis is a type of gastrointestinal illness.

  1. Describe the aetiological agent that causes salmonellosis. (1 mark)
  2. What is the incubation period for the disease? (1 mark)
  3. What are the symptoms of salmonellosis?(1 mark)

2. The authors state that a retrospective cohort study was used to investigate the outbreak.

  1. Explain what a retrospective cohort study is. (1 mark)
  2. What was the case definition for a confirmed case? (1 mark)
  3. Explain how routine (passive) surveillance and active surveillance (or active case finding) contributed to this investigation (1 mark)
  4.  Explain what "attack rate" and "relative risk" mean and how these led to identifying fried ice cream as the source of this outbreak (1 mark)

3. Explain what was involved in the laboratory and environmental investigations (2 marks)

4. Fried ice cream was identified as the source of the outbreak.
Explain why eggs are often implicated in cases of salmonellosis (1 mark)

5. Explain how the process of making fried ice cream contributed to this outbreak (1 mark)

6. Explain how the restaurant changed its process to reduce the risk following the outbreak(1 mark)

Part D (8 Marks) 

Read through the Guidelines for the Investigation of Gastroenteritis and answer all of the questions below. Each question is worth 1 mark.


https://www2.health.vic.gov.au/about/publications/researchandreports/guidelines-for-investigation-gastroenteritis-for-environmental-health-officersLinks to an external site.


  1. Identify the legislation which gives powers to EHOs to investigate infectious diseases in Victoria and briefly describe what is meant by the term ‘notifiable diseases’.
  2. Describe the privacy legislation which EHOs must be aware of when interviewing cases.
  3. Differentiate between a sporadic case, a cluster and an outbreak of gastroenteritis.
  4. Describe the key risk factors which must be examined when investigating a single incident case of gastroenteritis.
  5. Identify some of the common settings for gastroenteritis outbreaks. Suggest some reasons why gastroenteritis is easily spread in these settings.
  6. Describe the different routes by which outbreaks of gastroenteritis may be transmitted.
  7. Briefly explain what is involved in Environmental Cleaning following an outbreak of gastroenteritis and differentiate between cleaning and disinfection.
  8. Explain what Chain of Custody means and what it involves in relation to investigating outbreaks of gastroenteritis.

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