Question from a student 20160417a

Question

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From: YYYYY
Sent: Sunday, April 17, 2016 12:52 AM
To: hoishankwan@cuhk.edu.hk
Subject: Asking for FNSC3180 2012-2013 Q8

Dear Prof. Kwan,

If would be great that if u can help me to check my answer.

2012-2013 Q8b

From part (a) results, sushi get the loest difference rate -29%, it means that Vibrio parahaemolyticis is not included in this outbreak.

The incubation period  is 5-9 hour.

Pizza get a highest rate difference 25.4% , and the laboratory test small amount of bacillus cereus in the bread. The incubation period of bacillus is 1-6 , 8-16 hour, which match the attack time of patients. They also had the symptoms of diarrhea and vomiting. Since the bread is left at room temp. without refrigerated for a period of time, it has a high chance for bacillus proliferate.

Answer

You need to make your deduction with consideration of all information. The food impact analysis implied Pizza to be the source of the outbreak. So you need to see whether there is any other information supporting that. Although B. cereus in bread was detected and the incubation period fitted but the bread was clearly not implicated by the food impact analysis, it was probably some other pathogen was responsible. In this case, we can suggest that Staphylococcus aureus was responsible, because it may not be detectable in the implicated food, in thsi case, pizza, and the incubation period was consistent. 

You can get good marks if you discuss the whole scenario with good justification. Sometimes, the answer to the question may not be perfect, but that occurs in real life like that all the time. 

Best,

HS Kwan