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Volume 9, Number 5—May 2003

Research

Vero Cytotoxin–Producing Escherichia coli O157 Gastroenteritis in Farm Visitors, North Wales

Christopher J.I. Payne*Comments to Author , Marko Petrovic†, Richard J. Roberts†, Ashish Paul†, Eithne Linnane†, Mark Walker‡, David Kirby§, Anthony Burgess¶, Robert M.M. Smith*, Thomas Cheasty#, Geraldine Willshaw#, and Roland L. Salmon*1
Author affiliations: *Communicable Disease Surveillance Centre (Wales), Cardiff, Wales; †Department of Public Health, North Wales Health Authority, Mold, Wales; ‡Public Health Laboratory, Bangor, Wales; §Veterinary Laboratory Agency, Aberystwyth, Wales; ¶Isle of Anglesey County Council, Anglesey, Wales; #Public Health Laboratory Service Central Public Health Laboratory, London, UK

Main Article

Table 1

Results of univariable analysis of risks for illness caused by Escherichia coli O157 in visitors to an open farm, Walesa

Exposure Cases Controls Univariable analysis

Exposed/ not exposed
Exposed/ not exposed
Odds ratio
p value
95% CI
Contact with animals






Cows
11/2
16/20
6.88
0.01
1.15 to 52.69

Goats (any contact)
13/0
27/9
Undef
0.09
Undef

Goat (high contact)
10/3
17/19
3.72
0.06
0.75 to 20.70

Rabbit
9/4
20/16
1.80
0.39
0.40 to 8.62

Sheep
10/3
27/9
1.11
1.00
0.21 to 6.48

Pigs
5/7
11/24
1.56
0.72
0.33 to 7.32

Pony
4/9
20/16
0.36
0.12
0.07 to 1.61

Shire horse
4/9
13/23
0.79
1.00
0.16 to 3.64
Areas of farm visited






Play area
5/7
27/9
0.24
0.07
0.05 to 1.13

Paddock
6/7
28/8
0.24
0.08
0.05 to 1.13

Pony ride
4/9
15/21
0.62
0.49
0.13 to 2.84

Tractor ride
9/4
28/8
0.64
0.71
0.13 to 3.31

Main barn
13/0
35/1
Undef
1.00
Undef
Food consumption and personal behaviors


Sucks thumb
1/11
6/30
0.45
0.66
0.02 to 4.74

Bites nails
2/10
6/30
1.00
1.00
0.12to 7.08

Ate any food while on farm
13/0
33/3
Undef
0.56
Undef

Ate immediately after barn
6/6
11/23
2.09
0.31
0.45 to 9.81

Ate food bought on farm
8/5
14/21
2.40
0.18
0.55 to 10.85

Ate ice cream
9/4
14/22
3.54
0.06
0.77 to 17.19

Ate cotton candy
7/6
4/32
9.33
0.004
1.69 to 57.10

Bought animal feed
10/3
32/4
0.42
0.36
0.06 to 2.88

Picked up animal feed from floor
5/8
6/30
3.13
0.13
0.61 to 16.29

Ate animal feed
1/12
0/36
Undef
0.26
Undef

Clung to animal barriers
6/3
25/7
0.56
0.66
0.09 to 3.76

Fell over while on farm
1/12
7/29
0.35
0.66
0.01 to 3.43

Washed hands at all
10/3
24/9
1.12
1.00
0.23 to 7.35
Environmental observations






Wet underfoot
3/10
6/30
1.50
0.68
0.24 to 8.85

Dirty hands, shoes, or clothes
0/13
9/27
0.00
0.09
0.00 to 1.46

Noticed queue for toilets
2/10
3/32
2.13
0.59
0.21 to 19.56
Type of visit






Family visit
12/1
33/3
0.92
1.00
0.08 to 30.07
Bank Holiday Monday 11/2 13/20 9.73 0.003 1.38 to 66.32

aCI, confidence interval; undef, undefined. (When one of the cells contains a zero, defining a confidence interval is not possible.) Bold typeface highlights variables with increased odds ratio statistically significant at 90% level.

Main Article

1C. Payne designed the case-control study, drew up the questionnaire, and analyzed and wrote up the results. M. Petrovic helped design the questionnaire, organized the data collection, and wrote the sections describing the outbreak and microbiologic findings. R.J. Roberts contributed toward the study and questionnaire design, including devising the method of selecting controls; he also helped in the final drafts of the paper. R.L. Salmon originally conceived the study, commented on the questionnaire design, and helped interpret the findings. T. Cheasty was responsible for confirmation and typing of isolates. G. Willshaw performed DNA-based comparison of strains. Other authors made important contributions to the investigation and control of the outbreak and participated in writing the paper.

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