A Graduation Dinner with a Twist Case Study - Medical Science Assignment Help

Assignment Task:

Task:

Outbreak 3:
A graduation dinner with a twist
CASE HISTORY:
320 people, attended a students' graduation dinner. 3-48 hours later, people started becoming ill. Sadly, 4 elderly retired lecturers who suffered from the same symptoms, accompanied by severe dehydration, died. None of the catering staff were ill.
Questionnaires were sent out and information was received from 216 patients:
207 suffered from mild to severe abdominal pain,
193 complained of fever,
215 had diarrhœa,
35 experienced headache,
52 felt numbness of the extremities, and,
184 vomited quite severely.
The times of symptom appearance are given in Figure 1. The times of onset of symptoms (not included in Figure 1) for the four cases who died were 12 hours, 24 hours, 2 days and 2 days respectively.
Figure 1: Time to onset of symptoms in the graduation gastroenteritis outbreak from questionnaire. Times for the 4 fatal cases not shown (values:12, 24, 48, 48 hours).

39 hours onwards – outliers – Simply if you had a friend went to the graduation party – then they say they fell a little sick.

• Calculate incubation time.
• TABLE 1: Food-specific attack rates for 216 ill persons associated with the graduation gastroenteritis outbreak (reported by questionnaire).
• Persons Eating Food Persons Not Eating Food
• Relative Food Risk ILL Not ILL Total % ILL
• (attack rate) ILL Not
• ILL Total % ILL
• (attack rate)
• Beer 62 31 93 66.6 65 19 84 77.38
• Ice-cream 71 25 96 73.95 84 11 95 88.42
• Lemonade 59 32 91 64.8 61 16 77 79.22
• Roast beef 61 22 83 73.5 58 22 80 72.50
• Chicken salad 142 38 180 79.0 3 15 18 16.67
• Potato salad 48 35 83 57.8 72 31 103 69.90
• Oysters 26 12 38 68.42 120 15 135 88.88
• PREWORK: Before coming to class complete the following:
• Calculate the ODDS RATIO for each of the foods from table 1:
• Chicken Ill Not Ill
• Ate the food 142 38
• Didn’t eat the food 3 15
• ODDS RATIO: = 18.70
• Potato Salad Ill Not Ill
• Ate the food 48 35
• Didn’t eat the food 72 31
• ODDS RATIO: = 0.59
• Roast Beef Ill Not Ill
• Ate the food 61 22
• Didn’t eat the food 58 22
• ODDS RATIO: = 1.05
• Oysters Ill Not Ill
• Ate the food 26 12
• Didn’t eat the food 120 15
• ODDS RATIO: = 0.27
• Summary of information required (show all calculations).
• (a)The number of persons who were ill. The highest number from the patients who presented with all illness 215 + 4 people who died.
• (b)The percentage morbidity = 99.54% 215/216 x100
• For noting: 215/320 = 67.19% (%Morbidity from total at dinner – we know that those who don’t get sick are less likely to return questionnaire)
• (c)The percentage mortality = 1.25% 4/320x100
• (d)The percentage case fatality rate. = 1.86% 4/216x100
• TABLE 2: A. Symptoms reported by questionnaire respondents for the graduation outbreak.
•  
• 216 responded – everyone but one had diarrhoea =215
• 1 (Abdominal cramps)96.27%
• 2.(Chills) 4.56%
• 3.(Diarrhoea) 100%
• 4.(Fever) 89.77%
• 5.(Headaches) 16.28%
• 6.(Nausea) 69.77%
• 7.(Vomiting) 85.58%
• B. Duration of illness (for those where this could be reliably ascertained).
•  
• Length of the illness – First five days, by day six it drops off.
• Divide by 88
• Cumulative Patients (%)
• 1.5/88 = 5.58%
• 2.23/88 = 26.14%
• 3.36/88 = 40.91%
• 4.46/88 = 52.27%
• 5.59/88 = 67.04%
• 6.72/88 = 81.81%
• 7.79/88 = 89.77%
• 8.83/88 = 94.3%
• 9.84/88 = 97.3%
• 10.86/88 = 97.7%
• 11.87/88 = 98.86%
• 12.88/88 = 100%
• 13.88/88 = 100%
• (e)The average and median duration of illness
• (Hint for median – plot % cumulative duration against time)
• Average and median duration of illness = 4
• X Y
•  
• (f)The average and median incubation periods.
• 18.38 incubation period
•  
• (g)The symptoms which typified the outbreak
• The symptoms displayed by more than 50% of individuals. Fever, vomiting and severe abdominal pain and diarrhea.
• PROCEDURE
• The class is provided with suspect samples of chicken salad, potato salad, oysters and roast beef together with a faecal sample of a person who ate that food.
• Each group will investigate one food and one faecal sample from an individual who consumed that particular food you are investigating.
• 565151309370DAY 1
• 0DAY 1
• 577854241800DAY 3
• DAY 3
• 565152616835DAY 2
• DAY 2
• 58420561340DAY 0
• 0DAY 0
•  
• Make sure a culture is pure – API 20 going to be valid if its mixed -
• Another big discussion point - Salmonella infections are reportable to NSW Health
• If you discuss the limitations of questionnaires - please also comment on the strengths of using them
•  
• Whether or not if they have the same strain – to able to link it to the same case.
• Food - Day 0
• Steps 1 to 4 will be performed by Technical staff.
• 1.Weigh out 25 grams of food into a "stomacher" bag.
• 2.Add 225 mL Buffered Peptone Water to bag and homogenise in the "stomacher" for two minutes.
• 3.Incubate homogenate at 37?C for 18 – 24 hours.
• 4.Inoculate 1.0 mL of the buffered peptone water homogenate into Mannitol Selenite Cystine Broth (MSCB). Incubate at 37?C for 18-24 hours.
• Day 1
• Materials (per group)
• Food sample enriched in MSCB (Mannitol Selenite Cystine Broth)
• Faecal specimen
• 1 x 3 mL BPW (Buffered Peptone Water)
• 2 x MacA (MacConkey Agar)
• 1 x SSA (Salmonella Shigella Agar)
• 2 x XLD (Xylose Lysine Deoxycholate Agar)
• 1 x BSA (Bismuth Sulfite Agar)
• 1 x MSCB
• Food - Day 1
• Plate out the food enrichment cultures onto appropriate media for single, well-isolated colonies, MSCB onto BSA (Bismuth Sulfite Agar), MacA (MacConkey Agar) and XLD (Xylose Lysine Deoxycholate Agar).
• Incubate cultures at 37?C for 18-24 hours.
• Faeces
• Place the faecal specimen into 3.0 mL of peptone water and shake the specimen in the peptone water to disperse the material.
• Use the faecal suspension to inoculate MacA, SSA and XLD plates and plate out for single, well-isolated colonies.
• Add 1 mL of the peptone water suspension to MSCB.
• Incubate cultures at 37?C for 18-24 hours.
• Day 2
• Materials (per group)
• 1 x disposable pipette
• 1 x API 20E
• 1 x TSA for purity
• 1 x 10mL distilled water
• API 20E kit
• Food

1.Examine the food plates for suspect colonies of Enterobacteriaceae. Carry out Gram stain, catalase/oxidase tests. Identify your isolate as far as possible on the basis of these tests, growth conditions and colony appearance of every different colony.
2.Prepare a just turbid suspension of a suspicious isolate from the food specimens. Use this to inoculate the API 20E kit.
To confirm purity of the suspension used for your API 20E set up, streak out your suspension (from Step 2) onto a TSA (Tryptic Soya Agar) plate- this is known as your ‘purity plate’.
Ques: Why is a purity plate important?
4.Incubate all media at 37?C for 18 - 24 hours.
Faeces
1 x SSA
1 x HBA
Examine faeces plates for suspect colonies or purity. Carry out Gram stain, and catalase/oxidase tests. Identify your isolate as far as possible on the basis of these tests, growth conditions and colonial appearance.
Subculture a suspect colony on to a HBA plate for purity.
Subculture the faecal enrichment broth (MSCB) onto SSA.
Incubate all cultures at 37?C for 18-24 hours.
Results: Food Sample:
Xylose Lysine Deoxycholate Agar (XLD)

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