Module 2: Epi Summary

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Preliminary information and subject to change throughout the day – not for distribution

Case study: [2014-175] E. coli O157:H7 in MB, SK, AB and BC

Epidemiologic Summary, July 25, 2014 16:00 EDT

Table 1: Summary of confirmed cases

  Confirmed cases (n=12)

P/T Case Count

AB

MB

SK

BC

 

3

4

4

1

Age (years)

Range

Mean

Median

 

7–82

37

33

Sex:  % Female 50% (6/12)
Hospitalizations 38% (3/8)
Deaths 0% (0/8)
Onset date  range June 28 to July 7, 2014
PFGE pattern ECXAI.1398/ECBNI.1212

 

CASE DEFINITIONS:

 Confirmed case: A resident of or visitor to Canada with

  • Laboratory confirmation of coli O157:H7 AND
  • PFGE pattern combination ECXAI.1398/ECBNI.1212 AND
  • Symptom onset or laboratory confirmation on or after June 1, 2014

 Probable case: A resident of or visitor to Canada with

  • Laboratory confirmation of coli O157:H7 AND
  • PFGE pending AND
  • Symptom onset or laboratory confirmation on or after June 1, 2014

 Suspect case: A resident of or visitor to Canada with

  • Symptoms* consistent with coli O157:H7 infection AND
  • An epidemiological link to a confirmed case AND
  • Symptom onset on or after June 1, 2014

*Diarrhea (three or more loose stools within 24 hours)

module-2-epi-curve

Figure 1: Epidemic curve of confirmed cases by illness onset date and province (n=12)

BACKGROUND:

  • A review of the literature reveals that coli O157:H7 outbreaks have been associated with a wide variety of food products as well as animal contact and exposure to untreated water. Sources of outbreaks of over the last few years have included unpasteurized milk, apple cider, various lettuces (including romaine), spinach, ground beef and ground beef products, venison, and strawberries.
  • According to Outbreak Summaries, the last two coli O157:H7 outbreaks in Canada were associated with cheese made from unpasteurized milk and tenderized beef.
  • This pattern combination was reported four times in the past six years to PulseNet Canada and is considered rare.
  • FoodNet Canada and the US-CDC both report that they have not seen this PFGE pattern combination before.

 

EXPOSURE SUMMARY:

  • 8 out of 12 cases have been interviewed with the hypothesis generating questionnaire. The following foods were reported in higher than expected frequencies (See Table 2):
    • Vegetables: romaine lettuce, bell peppers, red bell peppers, cherry tomatoes, and mushrooms
    • Meat: hamburgers and bacon
    • Fruit: strawberries
  • 2 cases in SK report attending the same barbecue on Canada Day. Local public health has conducted an initial investigation into the two cases associated with a Canada Day BBQ; there are 5 other non-laboratory confirmed (clinical) cases that attended the BBQ that the health unit has begun interviewing (stool samples not provided at this time).The local public health investigation is focused on two different potential sources:
    • Romaine lettuce: the same brand has been consumed by all SK cases
    • Hamburgers: hamburgers served at the barbecue were both frozen and fresh, sources of the patties and ground beef is unclear at this point; public health is trying to obtain enough additional information to enable traceback.
  • The case from BC is a vegetarian.

 

FOOD SAFETY INVESTIGATION:

  • Traceback activities have begun for the romaine lettuce reported being eaten by cases in Saskatchewan.
  • The information obtained to date on the ground beef and frozen hamburgers is insufficient to start a full traceback. Local public health in Saskatchewan is trying to determine when and where the beef products were purchased.

Table 2: Food exposures of confirmed cases (n=8). Data source: PHAC hypothesis-generating questionnaires.

Food Item

Confirmed Cases

Reference A
(CDC Food Atlas, 2006-2007)

Reference B
(Waterloo Study. Nesbitt et al., 2008)

Reference C
(Foodbook Canada, 2015)

Binomial probability

Yes

Prob

No

DK

%Y+P

Using Reference A

Using Reference B

Using Reference C

VEGETABLES

Lettuce

6

0

0

1

100.00%

no data

 84.00%

82.40%

no data

0.3513

0.3130

Romaine

6

0

0

1

100.00%

46.50%

 no data

48.80%

0.0101

no data

0.0135

Bell Peppers

5

0

1

1

83.33%

no data

 27.03%

63.60%

no data

0.0063

0.2273

Red

5

0

1

1

83.33%

29.50%

no data

no data

0.0095

no data

no data

Orange

4

0

1

1

80.00%

no data

  no data

no data

no data

no data

no data

Yellow

1

0

1

1

50.00%

 no data

no data

no data

no data

no data

no data

Tomatoes (fresh, not grown at home)

5

1

1

0

85.71%

59.60%

72.51%

72.90%

0.1268

0.2797

0.2847

Cherry

3

1

1

1

80.00%

no data

 no data

32.80%

no data

no data

0.0389

Cucumbers

4

0

2

1

66.67%

46.90%

54.56%

62.90%

0.2046

0.2745

0.3232

Broccoli

4

0

2

1

66.67%

53.30%

43.38%

55.50%

0.2640

0.1703

0.2818

Mushrooms

5

0

1

1

83.33%

33.50%

36.46%

50.00%

0.0168

0.0246

0.0938

MEAT

Any beef (not including deli meat)

7

0

1

0

87.50%

no data

 78.65%

78.40%

no data

0.3180

0.3146

Hamburgers

7

0

1

0

87.50%

no data

35.88%

39.10%

no data

0.0039

0.0068

Bacon

4

1

3

0

62.50%

46.30%

no data

27.20%

0.1845

no data

0.0322

Any chicken (not including deli meat)

6

1

1

0

87.50%

64.90%

91.43%

85.60%

0.1362

0.3662

0.3879

Whole or cut chicken  pieces or parts

4

0

3

1

57.14%

no data

 no data 

70.00%

no data

no data

0.2269

DAIRY & EGGS

Ice-cream/gelato

4

0

2

1

66.67%

59.20%

42.82%

42.00%

0.3067

0.1649

0.1570

Eggs

4

1

1

0

83.33%

75.40%

82.22%

80.70%

0.3597

0.4008

0.3963

Did (you/case) handle any eggs (including eggs in their shells or raw or undercooked eggs) in the 7 days prior to illness?

4

1

1

0

83.33%

no data

 no data

no data

no data

no data

no data

FRUIT

Strawberries

4

0

1

1

80.00%

45.00%

31.54%

49.60%

0.1128

0.0339

0.1525

Bananas

4

1

2

0

71.43%

70.30%

79.04%

76.70%

0.3181

0.2846

0.3026

OTHER

Cold breakfast cereal

3

1

2

0

66.67%

69.20%

no data

54.30%

0.3263

no data

0.2723

Other prepackaged snack food (e.g., chips, pretzels, crackers, cookies, snack cakes)

4

1

1

0

83.33%

71.80%

no data

no data

0.3229

no data

no data

 

*Based on Population Survey Atlas of Exposures, 2006-2007, United States Centers for Disease Control and Prevention

†Based on Waterloo Region, Ontario food consumption survey, November 2005 to March 2006

++Based on the Foodbook Survey, 2015, Public Health Agency of Canada

 

Prepared by Centre for Food-borne, Environmental and Zoonotic Infectious Diseases, Outbreak Management Division, (CFEZID/OMD). This information is shared in confidence, further distribution should be done only in accordance with the Foodborne Illness Outbreak Response Protocol.

 

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