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Designing and conducting a
model investigation of foodborne
disease
Prepared by Dr Craig Dalton
Public Health Physician
For Viet Nam Food Authority 8th June 09
Outline
 What does “the model” outbreak investigation
look like
 How does the model outbreak support a model
food safety system
 What are the key needs to achieve the model
foodborne outbreak system
2
Start with a story…..
 Outbreak investigation is important because:
– Helps control current outbreak
– Helps us learn how to prevent future outbreaks
3
 In 1993, as a trainee foodborne
disease epidemiologist, I realised
that my 9 year old niece knew
more about the epidemiology of
Salmonella in the USA than I
knew about Salmonella in
Australia!
 I was trying to stop her brother
putting this frog in his baby sisters
mouth because it might cause
salmonellosis.
 She said: Uncle Craig,don’t worry
about frogs - eggs are the main
cause of Salmonella!
What makes a 9 year old so smart?
 Good outbreak investigations
 National database of foodborne outbreaks
 Good communication of problem:
– Foods
– Food preparation errors
– Settings
5
Salmonella outbreaks, USA, 1992
 80 Salmonella outbreaks
 60 outbreaks due to S. Enteritidis
 Eggs implicated in 22/25 (88%) with known food
 Deaths in nursing homes
 Recommendation: pasteurised eggs
Questions we couldn’t answer…
What is the commonest
cause of salmonellosis in
Australia?
Questions we couldn’t answer…
What is the major food handling error responsible for
foodborne disease in Australia ?
 ? Lack of handwashing
 ? Temperature abuse
We needed a national outbreak database
Outbreak report
Outbreak report
Outbreak report
No. ill: 35
Bug:
S. agona
Association:Relative risk of 9
Vehicle: Egg rolls
Contributing factors:
Temp abuse
Setting: Restaurant
No. ill: 35
Bug: S. agona
Association:RR of 9
Vehicle: Egg rolls
Cont factors:
Temp abuse
Setting: Restaurant
Every outbreak is a lesson in prevention
 A national database of foodborne outbreak data
is a database of “lessons” in prevention.
 Need good outbreak investigations to capture
these lessons – expert teams that mentor
 Standardised methods of investigation and
documenting the outbreaks.
– Manuals that help standardise practice
– Standard case definitions, questionnaires
– Standard data entry forms for national database
– Can be online
10
11
Standard
Outbreak Reports
• Pathogen
• Place
Training and
practice in
model
outbreak
investigation
methods
• Food
• Hygiene practices
12
Standardising questionnaires
 NetEpi – web based questionnaires
 Used in large distributed outbreaks
13
Using Outbreak Summary Data
 Summary data can inform policy work by other
agencies
 Summarise by commodity or by aetiology
 Important to feed back to regulation/intervention
– complex web of food production and food
safety
 Broader attribution efforts
14
Benefits
 HACCP food safety programs based on causes
of foodborne disease in your own jurisdiction
 Prioritise food safety policy based on true
morbidity and mortality NOT media or local
folklore
 Assess effectiveness of prevention programs
The Model
Foodborne Outbreak
Investigation
16
Steps of an outbreak investigation

Establish the existence of an outbreak

Verify the diagnosis

Defining and counting cases

Determining the population at risk

Descriptive epidemiology

Developing hypotheses

Evaluating hypotheses

Additional epidemiological, environmental and laboratory
studies

Implement control and prevention measures

Communicate findings
17
Establish existence of an outbreak
 Definition:
 a) The observed number of cases of a particular
disease exceeds the expected number.
 b) The occurrence of two or more cases of a
similar foodborne disease resulting from the
ingestion of a common food.
18
Verifying the diagnosis
 Diagnosis may be
– Syndromic e.g. vomiting and diarrhoea
– Laboratory
• Laboratory diagnosis helps ensure we are
comparing “apples with apples” rather than parasitic
diseases with bacterial diseases.
19
Defining and counting cases
 Case definition
– Time, person, place
 Case definition for salmonella outbreak
– Suspect : All persons with diarrhoea (3 or more loose stools)
and abdominal cramps within one week of attending the
feast.
– Confirmed case: suspect case with salmonella of same
serotype isolated from stool.
Depending on local epidemiology of salmonellosis we may
need salmonella serotyped or further subtyped to ensure
were are comparing “apples with apples”)
20
Gastroenteritis after an awards ceremony
 Approximately 3000 attendees
 Awards for State Emergency Services for
Thredbo landslide disaster response
 Reports from Hunter SES of diarrhoea 19 hours
post lunch
» Outbreak reported 3 days after luncheon
21
Established outbreak & case finding
 Multiple bus loads of Emergency Volunteers
returned all over the state
 Obtained a list of volunteer groups and contacted
them asking about symptoms
 Kept a team of 8 people back to 11pm calling
organisers, tracking down and interview cases and
well people.
 Many reported diarrhoea, no other common link
apart from the awards luncheon.
22
Verifying diagnosis
 No specimens available at time of report
 Clinical case definition:
– Attended luncheon at Governors mansion
– Onset of diarrhoea* within 3 days of luncheon
 Collected specimens
– Drove to cases houses
– Left stool collection kit
– Paged us when stool sample ready for pick up
23
Remove barriers to specimen collection
 call twice daily to check
 give written advice on how to collect stool
specimens
 provide containers, refrigeration block.
 pick up from patients home
 run a clinic
 consider rectal swabs
24
Descriptive epidemiology
 171 persons met the case definition
– defined as eating at the luncheon and reporting
diarrhoea that lasted more than 9 hours or
diarrhoea that was accompanied by abdominal
cramps or vomiting in the 3 days after attending
luncheon.
 Median incubation period 9 hours
– (range, 9 to 48 hours)
 Median duration of illness was 24 hours (range,
1 to 96 hours).
25
Descriptive epi - Symptoms
Diarrhoea
100%
Abdominal cramps
72%
Nausea
30%
Vomiting
15%
Fever

5%
So what pathogen is this symptom profile and incubation period
consistent with?
26
Environmental investigation
 Catered function prepared off site
 It was the largest function ever catered by this
caterer (3,000 people)
 Cooked foods days ahead
 Ran out of cool room space
 Food for lunch delivered into tents from 4am in
the morning and stored under tables and
consumed from 1pm to 4pm (up 12 hours after
delivery!)
 No food for testing
27
Food specific attack rates
– Awards Ceremony
Persons ate
specified food
Food
Ill/Total
Attack
rate
Persons did not
eat specified foods
Ill/Total
Attack
rate
Relative
95% CI
Risk
(%)
(%)
Chicken
116/194
60%
9/34
26%
2.3
1.3-4.1
Ham
111/187
59%
17/38
45%
1.3
0.9-1.3
Beef
110/176
63%
19/49
39%
1.6
1.1-2.3
Potato salad
103/169
61%
22/53
42%
1.4
1.0-2.0
Pasta salad
90/141
64%
32/70
46%
1.4
1.0-1.8
28
Dose response for chicken consumed by those
who reported ill after attending the luncheon
Chicken
servings
Ill
Not
ill
Relative
risk
1
8
Reference
1
17
17
4.5
0.6-29.4
2
7
1
7.8
1.2-50.9
N= 49
0
95% CI
29
Laboratory results
 Disaster! Stool samples lost for 2 days
 Stool samples had low counts of clostridium
perfringens spores (< 106 spores per gram)
 Laboratory comes to our rescue with Pulsed
Field Gel Electrophoresis
30
PFGE of C. perfringens outbreak
 .
Similar pattern suggesting
common exposure
31
Prevention
 Food inspector blitz on caterers
 Entered into our database
– Yet more evidence that “weekend” and “offsite”
catering is associated with outbreaks due to
inadequate temperature control
32
Was this a model outbreak?
 Common pathogen
 Good and rapid case finding
 Aggressive collection of stool specimens
– Did not rely on health clinics or hospitals
 Epidemiological techniques including doseresponse analysis helped identify the chicken
 Close liaison with laboratory enabled novel
testing that confirmed cause
33
Benefits of OzFoodnet Oubreak
Register
34
National Outbreak Register
• Outbreak register
• Centralized collection of outbreak reports
• Retrospective
• Data collected one quarter in arrears
• Accuracy and completeness
• Data accessible through ad hoc data requests
35
Outbreak Register – Key Fields
 Outbreak sequence number
 Year, first case onset, last case onset
 State
 Number ill, hospitalised, died
 Setting food prepared
 Mode of transmission
 Vehicle
 Remarks
36
Outbreak Register – Data
 Updated to September 2007 (except VIC)
 4688 outbreaks
– 638 (14%) foodborne or suspected foodborne
– 3598 (77%) person to person
– 108,421 people ill
– 3058 hospitalised
– 120 deaths
37
Foodborne Outbreaks, 2001- Sep 2007
 638 foodborne or suspected foodborne outbreaks
– 10,424 people ill
– 815 hospitalised
– 13 dead
 Setting
– 40% in restaurants
 Aetiology
– 31% Salmonella species
• 73% Salmonella Typhimurium
– 39% Unknown
38
External Data Requests
 Requests received from
– Industry partners
– Government partners
– General public
– Academics
 Many parties interested in the data
39
Case Study: Egg Associated Outbreaks
40
Egg-Associated Outbreaks
 75 egg-associated outbreak reports from January
2001 to April 2007
– 1222 cases, median 9.5 (2-213)
– 361 hospitalised, 3 deaths
 Data provided to FSANZ Standards Development
Committee (developing primary production
standard)
41
Egg-Associated Outbreaks, 2001 – April 2007
20
18
18
16
Number of Outbreaks
16
14
12
11
11
9
10
8
6
6
4
4
2
0
2001
2002
2003
2004
2005
2006
2007
Year
42
Enhanced Data, Egg-Associated Outbreaks
 Collected enhanced data on 67 of 75 egg-associated
outbreaks
 58% (39/67) associated with uncooked eggs
 84% (56/67) Salmonella Typhimurium
 37% (25/67) had environmental testing of farm
– 76% (19/25) of these were positive for Salmonella (many
serotypes)
 28% (19/67) - sampled eggs from farm
– 31% (6/19) of tested eggs were positive for Salmonella
 Outbreak register helps define risk factors, environmental
conditions and completeness of public health response
43
Key Themes
 Increase in egg-associated outbreaks
• Catering industry (raw egg use)
• Bakeries including “Vietnamese Style”
• Private homes (raw egg use)
 Improving investigation
• Same strains in patients & farms
• Greater understanding of egg types and sources
 Intervention for prevention
• Egg Food Safety Summit
• Primary Production & Processing Standard
44
Evidence supports government statements on eggs
45
Deaths by setting (n=20)
Hospital
15%
Fair,
temporary
5%
Aged care
20%
Restaurants
20%
Commercial
caterer
5%
Contaminate
d primary
produce
10%
Commercial
manufactured
25%
46
Integrating high risk foods and setting risk
Ministerial Policy Guidelines on Food Safety
Management in Australia: Food Safety Programs
www.foodsecretariat.health.gov.au/pdf/food_safety.pdf
47
Data used for decision making…

Summaries of multiple outbreaks of Individually Quick Frozen Oyster
meat from Japan and Korea were used to convince regulators that
the risks posed by these foods was too high.

Standard setting for foods such as
–
–
–
–
–
chicken
meat,
eggs,
dairy products and
seafood.

Deaths associated with foodborne outbreaks in aged-care facilities
and hospitals supported Food Safety Programs for Service to
Vulnerable Persons

Data used for quantitative risk assessment

Number of outbreaks of “unknown pathogens” highlights need to
improve specimen collection and laboratory capacity
48
Summary
 Good outbreak investigation requires:
– Training
– Mentoring
– Lots of practice
– Standardised case definitions, data handling and
reporting
– Enthusiastic field investigation including
environmental inspection and clinical specimen
collection
 All outbreaks summarised in national database
to provide ongoing lessons for prevention.
49
Thank you
 Acknowledge the assistance and work of others
in investigation of these outbreak, compiling
data and contributing presentation material Mary Osbourn, Philip Bird, Martyn Kirk, Katie
Fullerton and OzFoodnet epidemiologists.
50