Case study - Outbreak of food poisoning at scientific conference.

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Case Study

“Outbreak of food poisoning at scientific conference”

In order to investigate the outbreaks described, the following table (table 1) was presented. The table concentrate at the critical points of the outbreak. The range of onset illness was generated in the table as the incubation period of unknown micro-organism. The duration of the reported symptoms from victims was generated as the duration of illness. The temperature at which the sample was held was generated in the table as environment.

Table1. Critical points of the outbreak

From the critical points given on the table 1, it could be assumed that the micro-organisms that could be involved in this outbreak were Salmonella enterica (S. enterica), Escherichia coli (E.coli) or Campylobacter jejuni (C. jejuni). These micro-organisms are very common cause of food poisoning and they have very similar properties. They are Gram –ve rods. S. enterica and E. coli are facultative anaerobic micro-organisms and they temperature range is 10 ºC - 45 ºC. They optimum temperature is at 37 ºC and the maximum at 70 ºC. C. jejuni is thermotolerant and microaerophilic micro-organism which has optimum temperature at 45 ºC. The incubation time in which S. enterica develops symptoms is 12-48 hours, where E.coli requires 24-48 hours and C. jejuni 2-5 days.

The common symptom which can cause these micro-organisms is diarrhoea. S. enterica is usually associated with diarrhoea and vomiting. E. coli infection is usually present diarrhoea and dysentery, where C. jejuni present diarrhoea and fever.

The food sources that can cause S. enterica infection are daily products like poultry, eggs, food handlers, beef and unpasteurised milk. E. coli infection can be caused by water, raw vegetables, fruits, and unpasteurised dairy products. The food sources that can cause C. jejuni infection are shellfish, unpasteurised milk, poultry and meat.

When the infection of S. enterica occurs, the duration of the illness is usually 4 to 7 days. In case of E. coli the duration of the illness is 3 to 4 days and for C. jejuni is usually 2 to 5 days.

In order to define the micro-organism which caused the outbreak, the given information in the table 1 were compared to the micro-organisms discussed above.

Since the incubation time for E.coli to develop symptoms is 24-48 hours and for C. jejuni is 2-5 days they could not be the one micro-organism wanted. Also C. jejuni is thermotolerant micro-organism. S. enterica and E. coli temperature range is 10 ºC - 45 ºC which is the closets to this case. E. coli infection is usually transmitted by water, raw vegetables, fruits, and unpasteurised dairy products which in this case are not the sample which have been examined. From these investigations, the hypothesised micro-organism caused the outbreak was S. enterica. 

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Salmonella can be passed from animal products to human, from animals to animals, and by oral route. This bacterium causes enteritis, enteric fever and systemic infection. The diagram 1 shows the cycle of Salmonella infection.

The cycle of Salmonella infection

Environmental                              Products eaten

Pollution                                     by humans


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