BMS5002 Infectious diseases

BSc Biomedical Sciences

Department of Life Sciences

BMS5002 Infectious diseases

Module assessment #1 2020-21

Food-poisoning case studies


TITLE          :                            Outbreak case study


ASSESSED:                   Describe some of the important pathogens that cause

human infections.

Understand the importance of food as a source of infection and gastrointestinal infections in general.

Communicate effectively in writing


TO ELEMENT:                50% of whole module

SUBMISSION:               Upload link in BMS 5002 Moodle page


SUBMISSION DATE      12:00 midday, Wednesday 28th July 2021

FEEDBACK                     Coursework upload link in BMS5002 module page on

METHOD:                       Moodle

NOTE:                            The usual University penalties apply for late submission and plagiarism. Please consult your student handbook for further details.

I. Assessment Requirements

This assessment is based upon the public health part of this module and is supported by the lecture content provided from week 22.  Further support and information will be found in the workshop sessions that were held in week 24. All workshops and lectures were recorded and can be found on Moodle. This assessment is based around two case studies. CAREFULLY read the two case studies and write a report addressing the points provided.  You should write up to 750 words for each case study.  Assignments must be written using Microsoft Word. Write the assignment as a new document; do not include the information provided in the scenarios as you will use-up your word limit. Tables, figures and references do not count towards the word-limit.

The final report should be submitted electronically to the BMS5002 module page on Moodle by 12:00 on Wednesday 28th July 2021.

Submissions handed-in after the deadline WILL NOT BE MARKED AND WILL BE AWARDED ZERO MARKS.

II. Assessment Scenario/Problem

This assessment addresses the following Module Learning Outcomes:

  • Correctly identify the causative agents in a range of food poisoning scenarios.
  • Summarise the key clinical tests for identifying a range of microbes and the associated therapeutic strategies.
  • Explain how epidemiology is used to monitor populations for changes in infectious disease trends and trace the source of outbreaks.

Outbreak case study

Read through the two outbreak case studies given below and produce a report in which you should discuss each outbreak considering the following points:

  1. What organism do you suspect has caused the outbreak and why? In your report you should consider the incubation period, what symptoms were reported, the foods involved and groups of population affected? Any other useful information of relevance. Note there may be more than one probable cause in some cases. Why have you ruled out certain organisms?
  • Which food is likely to be the source and why? You should consider the type of food and features of the suspected organism that make this food a more likely source.
  • What advice would you provide to the food handlers to prevent this type of outbreak from happening again?
  • If you feel that more than one organism or food could be responsible for the symptoms described, explain what tests would you perform to confirm the identity of the causative agent or most likely food and why?

You should cite any external sources that you have used for information within the text and provide a reference list at the end of the report (this will not be considered as part of the word count). VERY IMPORTANT: support all your hypotheses with references to published articles. For example, if you think a particular pathogen was responsible for causing the outbreak and had contaminated a particular food, cite references to support your conclusions.

When sourcing material to support your hypotheses, avoid using web-sites that do not contain peer-reviewed material such as WebMD, Mayo Clinic, Wikipedia etc as you may be penalised. However, official web-sites such as government organisations (eg Health Protection England (HPE), World Health Organisation (WHO), European Communicable Diseases Centre (ECDC) etc) containing verifiable data are acceptable.

Please use the marking criteria listed at the end of this assignment to help you understand how marks are assigned.

Case 1

In July 2006, environmental health officials were called to investigate an outbreak of food poisoning at a village in Cambridgeshire, UK. The village comprises 5000 inhabitants and is located next to a nature reserve which includes several flooded gravel pits that are now used for water sports activities. There is also a forest which has numerous trails for horse riding and cycling. It is therefore a popular destination for visitors. As a consequence of these attractions, the village built a camp site near the reserve to accommodate visitors. During the food poisoning outbreak, 45 people reported symptoms comprising 10 residents from the village and 35 visitors. Adjacent to the nature reserve is a farm that produced a wide range of organic fruits, vegetables and ice cream made from milk produced at the farm that were sold at a local Farmers’ Market. This was very popular with the local inhabitants and also the visitors in the camp. For one week in July 2006, commencing on Sunday 23rd July, a special festival was organised where local produce from the farm was sold. An epidemic curve was constructed (Fig. 1) and suggests that the outbreak may have coincided with the festival.

Symptoms experienced by people suffering from food poisoning comprised: watery diarrhoea (100%), abdominal cramping (88%), nausea (68%), fever (54%), vomiting (24%) and bloody diarrhoea (20%). The patient age range was 7 to 79 years. The median duration of symptoms was 8 days (range 2 – 14 days). Three patients were hospitalised as a precaution but all made a full recovery. Table 1 below, contains a list of all the foods consumed.

Table 1. Foods consumed during the outbreak. The table contains information about the numbers of people who ate the food and became ill as well as the numbers of people who did not eat the food but became ill. This is used to calculate the percentages who became ill following consumption of the food and those who became ill despite not eating the food. Calculate these percentages and use this information to calculate the Odds Ratio which tells us how likely each food was to have caused the food poisoning outbreak. You should show how you calculated the Odds Ratios. Explain how we can apply this information to solve the likely source of the contamination.

Note: you will find help on calculating odds ratios and attack rates on Moodle in the PowerPoint used in the workshop supporting this assignment.

Case 2

On 30th August 2014, 22 individuals who had participated in an elite sporting event in Sydney, Australia experienced gastrointestinal symptoms after eating a buffet dinner served by the commercial catering company servicing the event. The day of the outbreak was the final day of the two week event and reportedly less busy at dinner time than previous meals. The 22 individuals were part of a larger cohort of up to 40 people who queued for dinner service earlier than the other 500 attendees due to the timing of their responsibilities at the event. Within hours of eating, all 22 fell ill with symptoms including vomiting, diarrhoea and abdominal cramping. Six people were transported to hospital.

A total of 36 persons who ate an early dinner served by the caterer were interviewed. The median age of people interviewed was 40 years (range 12 to 72 years); 78% were female. Among the 36 persons interviewed, 22 (61%) were identified as cases (82% female, 18% male), including two persons with laboratory-confirmed illnesses. The age range of the cases was 12 - 69 years (median 34 years). The cases all dined between 16:00 - 17:30 on the day in question. Figure 2 shows the timing of symptom onset following the meal. Incubation periods ranged from 1 hour to 4.75 hours (average 2.5 hours). Illness typically began with the sudden onset of vomiting, followed by a period of concurrent vomiting and diarrhoea, with a median duration of 4 hours (range 2 to 13 hours). Of the 22 cases, 21 experienced vomiting (96%); 17 had diarrhoea (77%) and 10 reported abdominal cramping (46%).

Figure 2: Number of cases of gastrointestinal illness after dinner on 2 June 2012, by time of onset (n=22)

Dinner comprised a buffet-style selection of bread, cold meats (ham, chicken, turkey and roast beef), salad and fries. When the Environmental Health Inspectors visited the premises following notification of the outbreak, it was noted that one of the staff preparing the food had infected eczema on her hands.