Background:

The most frequent application of Relative Risk Analysis is in the identification of the specific food or foods potentially responsible for food poisoning outbreaks. These are sudden events where it is essential to identify and detain (remove public access to) the suspect food item or items as soon as possible to prevent further cases at that event, or further afield if the food comes from a bulk supplier. In countries where this is not effectively done, food poisoning outbreaks have been responsible for thousands of cases and sometimes many deaths. Even in Australia, we think that food poisoning may cause more absenteeism than influenza. Unfortunately, microbiological samples of the food eaten seldom gives a result in time to be useful because transport, incubation and identification can take up to 72 hours, and by this time the outbreak may have run its course. Another problem of standard microbiology is that the bacteria which produced the toxin (the causative agent) are often destroyed by cooking and are therefore not detectible in the micro lab, while the toxin remains active, causing further cases.

The exercise:

As food hygiene officer you are telephoned at home on Saturday evening by your departmental director because 84 of the 146 physiotherapists who attended a banquet a few hours earlier at a hotel have become violently ill with nausea and repeated vomiting, some vomiting in the dining room itself. They did not eat together prior to the banquet and are from different places of work. A few of the older guests have collapsed from dehydration and have been rushed to hospital, although no deaths have occurred.

With a team of trained interviewers, you visit all the guests and collect the following information regarding each item of food eaten:

Food item	Guests ill after consuming the item	Guests not ill after consuming the item
Turkey steak	25	26
Tomato and basil soup	18	2
Surf and turf	11	42
Vegetarian mushroom lasagne	13	60
Pavlova	30	0
Coffee	38	32

Part 1: Carry out relative risk analysis on the data provided and rank your results from highest to lowest. Show all tabulations and calculations.

Part 2: From the types of food most effected, the probable incubation period of the illness, and the symptoms, deduce and name the food poisoning type most likely to have been involved. Name this type and explain your reasoning based on the factors considered.