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Designing and conducting a model investigation of foodborne disease Prepared by Dr Craig Dalton

Public Health PhysicianFor Viet Nam Food Authority 8th June 09

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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

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Start with a story…..

Outbreak investigation is important because:

– Helps control current outbreak

– Helps us learn how to prevent future outbreaks

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!

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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

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

What is the commonest

cause of salmonellosis in

Australia?

Questions we couldn’t answer…

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 reportNo. ill: 35Bug: S. agonaAssociation:Relative risk of 9Vehicle: Egg rollsContributing factors:

Temp abuseSetting: Restaurant

Outbreak report

Outbreak reportNo. ill: 35Bug: S. agonaAssociation:RR of 9Vehicle: Egg rollsCont factors:Temp abuseSetting: Restaurant

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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

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Training and practice in

model outbreak

investigation methods

Standard

Outbreak Reports

• Pathogen

• Place

• Food

• Hygiene practices

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Standardising questionnaires

NetEpi – web based questionnaires

Used in large distributed outbreaks

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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

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

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The Model Foodborne Outbreak

Investigation

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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

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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.

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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.

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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”)

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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

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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.

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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

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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

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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).

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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?

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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

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Food specific attack rates – Awards Ceremony

Persons ate specified food

Persons did not eat specified foods

Food Ill/Total Attack rate

(%)

Ill/Total Attack rate

(%)

Relative

Risk

95% CI

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

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Dose response for chicken consumed by those who reported ill after attending the luncheon

Chicken servings

N= 49

Ill Not ill

Relative risk

95% CI

0 1 8 Reference

1 17 17 4.5 0.6-29.4

2 7 1 7.8 1.2-50.9

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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

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PFGE of C. perfringens outbreak .

Similar pattern suggesting common exposure

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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

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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 dose-response analysis helped identify the chicken

Close liaison with laboratory enabled novel testing that confirmed cause

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Benefits of OzFoodnet Oubreak Register

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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

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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

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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

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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

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External Data Requests Requests received from

– Industry partners

– Government partners

– General public

– Academics

Many parties interested in the data

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Case Study: Egg Associated Outbreaks

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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)

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Egg-Associated Outbreaks, 2001 – April 2007

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11

6

9

18

16

11

0

2

4

6

8

10

12

14

16

18

20

2001 2002 2003 2004 2005 2006 2007

Year

Nu

mb

er o

f O

utb

reak

s

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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

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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

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Evidence supports government statements on eggs

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Deaths by setting (n=20)

Restaurants20%

Commercial manufactured

25%

Aged care20%

Fair, temporary

5%

Hospital 15%

Commercial caterer

5%

Contaminated primary produce

10%

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Integrating high risk foods and setting risk

Ministerial Policy Guidelines on Food SafetyManagement in Australia: Food Safety Programswww.foodsecretariat.health.gov.au/pdf/food_safety.pdf

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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

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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.

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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.