2009 Outbreak_Investigation.food Borne Ppt

7/31/2019 2009 Outbreak_Investigation.food Borne Ppt

1/72

Outbreak Investigation:

Discussion Group


2/72

Initial Call

Late June, 1997: Calls from 4 MDs

reporting 6 patients with bloody diarrhea

andE. coli

O157:H7 infection


3/72

Initial Call

Late June, 1997: Calls from 4 MDs

reporting 6 patients with bloody diarrhea

andE. coli

O157:H7 infection 1 day later: Call from Michigan Department

of Community Health (MDCH)

Increase in laboratory reportsofE. coli O157:H7

June 1997 = 52


4/72

First.


5/72

Steps in Outbreak Investigation

1. Verify the Diagnosis


6/72


Escherichia coli O157:H7 first identified as ahuman pathogen in 1982 in the US

Sporadic infections and outbreaks since reportedfrom many parts of the world (e.g., N. America,

Western Europe, Australia, Asia, and Africa) Cattle are the primary reservoir forE. coli

O157:H7

Implicated foods are typically those derived fromcattle (e.g., beef, hamburger, raw milk);

Infection has also been transmitted throughcontact with infected persons, contaminated

water, and other contaminated food products.


7/72


Infection withE. coli O157:H7 is diagnosed

by detecting the bacterium in the stool.

Only recently hasE. coli O157:H7 infection

become nationally notifiable in many parts

of the U.S.


8/72




9/72


1. Verify the diagnosis

2. Confirm the outbreak


10/72

Trends in MDCHE. Coli O157 Cases

0

10

20

30

40

50

60

J J A S O N D J F M A M J

# Cases

1996 1997


11/72

What could account for the

increase in cases?


12/72

What could account for the

increase in cases?

Real increase

Increase in population size

Changes in population

characteristics

Random variation

Outbreak

Artificial increase

Increased cx of stools

New testing protocol

Contamination of cxs

Changes in reporting

procedures


13/72

Initial Investigation

No substantial changes in population size

No appreciable changes in the population

characteristics

No laboratory based changes

Surveillance / testing

Reporting protocol


14/72

Initial Investigation

Any other way to see if there is a

relationship between theseE. coli isolates?


15/72

Molecular Epidemiology

DNA fingerprinting

Pulsed Field Gel Electrophoresis (PFGE)

most common in outbreak investigations

A cluster of isolates with the same PFGE

pattern suggests they arose from the same

parent (same source)

Still need an epidemiologic investigation


16/72

PFGE pattern ofE. coli Isolates

Controls

in lanes

1,5,10


17/72

Molecular Epidemiology ofE.

coli Isolates 17 of the first 19E. coli O157:H7 isolates

from June-July were indistinguishable.

They did not match any fingerprints from a

convenience sample of isolates from

patients withE. coli O157:H7 infection

before May.


18/72





19/72




3. Case definition


20/72

3. Develop a Case Definition

Incubation period forE. coli O157:H7 rangesfrom 3-8 days with a median of 3-4 days.

The infection often causes severe bloody diarrhea

and abdominal cramps, but can also cause a non-bloody diarrhea or result in no symptoms.

In some persons, particularly childrenunder 5 years of age and the elderly,

infection can be complicated byhemolytic uremic syndrome(occurs in about 2-7% of infections)


21/72

Case Definition?


22/72

Case Definition

Outbreak investigation definition:

1. diarrhea (>3 loose bowel movements a day)

and/or abdominal cramps

2. resident of Michigan

3. onset of symptoms between June 15 and July 15

4. stool culture yieldingE. coli O157:H7 with the

outbreak strain PFGE pattern.

Advantages? Disadvantages?


23/72

Case Definition Advantages:

Lab confirmation increases specificity of case definition Reduces misclassification; maximizes power to detect source.

Disadvantages:

Lab confirmation

Excludes patients who didnt see MD, were not cxd, or cxd without PFGE. Decreases the sensitivity of the case definition

Possibly leads to a misrepresentation of case characteristics.

Limiting cases to Michigan residents

excludes visitors who became infected; inhibits recognition of extensionof outbreak into other states.

Dates reasonable?

Need more information

Could limit the number of secondary cases included in the study that could

interfere with identification of the initial source of the outbreak.


24/72


Verify the diagnosis

Confirm the outbreak

Case definition


25/72




Case definition

Descriptive Epidemiology


26/72

Characterization of Cases

Age group(years)

GenderTOTAL

Male Female

0-9 2 (17%)* 2 (8%) 4 (11%)

10-19 2 (17%) 3 (12%) 5 (13%)

20-39 3 (25%) 9 (35%) 12 (32%)

40-59 2 (17%) 8 (31%) 10 (26%)

60+ 3 (25%) 4 (15%) 7 (18%)

TOTAL 12 (101%) 26 (101%) 38 (100%)

* percentages refer to column totals.

Of the initial 38 persons who met the case definition, 26 (68%)

were female with a median age of 31 years.

Table 1. Age group and gender distribution for persons withE. coli O157:H7

infection (with PFGE pattern), Michigan, June 15 - July 15, 1997. (N=38)


27/72

APPENDIX 1

Age group(years)

Gender

TOTAL

Male Female

0-


28/72

Michigan counties

The 38 cases ofE.

coli O157:H7

infection meeting

the investigation

case definition

were reported

from 10 countiesin the lower

peninsula of

Michigan.


29/72

Epidemic Curve

Figure 3. Date of illness onset for persons withE. coli O157:H7 infection

and the outbreak PFGE pattern, MI, June 15 - July 15, 1997. (N=38)


30/72

Epidemic Curves

How to set it up

What it tells you

Mode of transmission Propagated

Common source

Timing of exposureCourse of exposure


31/72

Epidemic Curves

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10 11 12

Week

Cases

Propagated source: single exposure, no secondary cases

(e.g., measles)


32/72

Epidemic Curves

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6 7 8 9 10 11 12

Week

Cases

Propagated source: secondary and tertiary cases (e.g.,

hepatitis A)


33/72

Epidemic Curves

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10 11 12

Days

Cases

Common source: point exposure (e.g., salmonella)


34/72

Epidemic Curves

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10 11 12

Days

Cases

Common source: Intermittent exposure (e.g.,

contaminated blood product)


35/72

Epidemic Curve

Figure 3. Date of illness onset for persons withE. coli O157:H7 infection

and the outbreak PFGE pattern, MI, June 15 - July 15, 1997. (N=38)


36/72




Case definition Descriptive epidemiology


37/72




Case definition Descriptive Epidemiology

Develop a hypothesis


38/72

Developing a Hypothesis


39/72

Ask questions!!

But of whom.

And when...


40/72

Determining the Probable Period

of Exposure

Mean/Median incubation period

Minimum/maximum incubation period


41/72

Estimating date of exposure

0

1

23

4

5

6

7

8

9

10

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Days

Cases

Peak

One incubation period

Rubella = 18 days

Probabletimeofe

xposure


42/72

Estimating date of exposure

0

1

23

4

5

6

7

8

9

10

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Days

Cases

Maximum incubation

21 days

Minimum incubation

14 days

Probabletimeo

fexposure


43/72

E. Coli Epidemic Curve

Figure 3. Average incubation period = 4 days ( range 3-8 days)


44/72

Focus of Questions demographic information

clinical details of the illness with date of onset,duration, and severity of symptoms

visits to health care providers or hospitals, and laboratory

results

a complete food history in the last 7 days

water exposure in the last 7 days (e.g., drinking

water, exposure to recreational waters)

exposure to other ill persons in the last 7 days

exposure to children in day care in the last 7 days

exposure to a farm or farm animals in the last 7 days

travel outside the immediate area in the last 7 days


45/72

Interview ResultsVariable Cases (n=38)

Female 26 (68%)Med Age 31Rec water exposure 13 (34%)Other Ill person 6 (16%)

Day care 18 (47%)Farm 2 (5%)Fair 18 (47%)Travel 9 (24%)

Hamburger 25 (66%)Meat 22 (58%)Milk 32 (84%)Alfalfa sprouts 19 (50%)Lettuce 24 (63%)


46/72

Findings Thus Far

Cases are spread over 10 counties

No uniform attendance at any common event

Onset of symptoms among known cases extends over

approximately one month.

The median age of patients is 31 years (range 2-

76); 68% of cases are among females.

Factors present in over 50% of cases: Female, milk, hamburger, lettuce, alfalfa sprouts

Role of fair attendance, water exposure?


47/72

Hypothesis?


48/72

Hypothesis of Investigators

Lettuce and/or alfalfa sprout consumption is

associated withE. coli

infection


49/72







50/72






Test the hypothesis


51/72

Pick a Control Group


52/72

Controls Selected

2 controls selected for every case

Matched to the case by:

Age group

(0-


53/72

Methods to Identify Controls

Random digit dailing

Neighborhood controls

Other patients of same physician


54/72

Selection of Controls

The investigators identified controls for the studyusing random digit dialing.

Exposure information among cases was collected

for the 7 days before onset of illness. For controls, exposure information was collected

for the 7 days before the interview and for the 7

days before the onset of illness in the matching

case.

Twenty-seven case-control sets were interviewed;

the remaining case-patients could not be reached.


55/72

Interview ResultsVariable Cases (n=27) Controls (n=54)

Female 18 (67%) 36 (67%)

Med Age 31 31

Rec water exposure 9 (33%) 21 (39%)

Other Ill person 6 (22%) 9 (17%)

Day care 16 (59%) 33 (61%)Farm 2 (7%) 2 (4%)

Fair 12 (44%) 24 (44%)

Travel 8 (30%) 13 (24%)

Hamburger 17 (63%) 36 (67%)

Meat 14 (52%) 26 (48%)

Milk 21 (78%) 44 (81%)

Alfalfa sprouts 15 (56%) 4 (7%)

Lettuce 18 (67%) 34 (62%)


56/72

E. coli and Alfalfa Sprouts?

Variable Cases Controls OR (95%CI)

15 (56%) 4 (7%) 25 (4-528)

No other food item was significantly associated with

illness.


57/72






Test the hypothesis


58/72




Case definition

Descriptive epidemiology


Test the hypothesis

Refine hypothesis / Execute additional studies


59/72

Refine Hypothesis/Additional Studies

What control measures might you consider at this

point?

What further studies might you do?


60/72

Additional Studies

Culture implicated sprouts

Traceback study

distributor, processor, and producer; examination of thechain of production of the sprouts from the farm to the

table

Applied research onE. coli

research on alfalfa sprouts and survival/growth of E.coli O157:H7 (e.g., the ability of E. coli to survive and

grow on alfalfa seeds/sprouts at each step of the

production process).


61/72

Traceback Studies

Often necessary to identify sources of contaminationand quickly limit a public health threat by removingthese sources.

Ascertain the distribution and production chain for afood product to facilitate effective recall.

Clarify the point or points at which the implicated

food was likely to have become contaminated


62/72

Traceback Results

F ll


63/72

Follow up The implicated seed lot was a blend of 5 lots from fields of

four farmers and was harvested between 1994 and 1996.The seed processor and the farmers were located in Idaho.

Inspection of the alfalfa fields revealed three possible

sources of contamination: cattle manure, irrigation water,

and deer feces. Manure is not normally applied to alfalfa fields in Idaho

Cattle feed lots were common in this area and the alfalfa fields of

one farmer were adjacent to a feed lot.

Manure may have leaked or been illegally dumped onto the alfalfa

fields or run-off water from neighboring fields, contaminated by

manure, may have been used to irrigate the alfalfa fields.

In addition, three of four farmers occasionally saw deer in their

fields and one field was situated next to a wildlife refuge.


64/72


Verify the diagnosis Confirm the outbreak

Case definition

Descriptive epidemiology Develop a hypothesis

Test the hypothesis



65/72




Case definition



Test the hypothesis

Refine hypothesis / Execute additional studies Implement control and prevention measures


66/72

What interventions are Needed?

2 issues:

1) the immediate problem with this

implicated lot of seed2) the larger issue of seed sprouts as

vehicles for pathogenic

Wh i i N d d?


67/72


Implicated seed lot

all remaining seeds and alfalfa sprouts from the implicated

lot should be removed from the market.

Persons who have purchased sprouts from the implicated lot

should be instructed to destroy any remaining sprouts or return

them to the store at which they were purchased.

The producers of these particular seeds should be informed

of the need to protect alfalfa and other seeds used in

sprouting from contamination during growing, harvesting,and packing.

Specific sources of contamination should be identified and

eliminated from these growing sites.

Wh t i t ti N d d?


68/72


Seed sprouts are high risk vehicle for foodborne diseases

Continue applied research to find ways to successfully

decontaminate the seeds/sprouts.

Educate sprout growers on appropriate growing conditions and

handling of sprouts to limit contamination.

Educate the public about the riskiness of sprouts

Persons at high risk for complications of infection (e.g., children


69/72


Verify the diagnosis Confirm the outbreak

Case definition

Descriptive epidemiology Develop a hypothesis

Test the hypothesis


Implement control and prevention measures


70/72




Case definition



Test the hypothesis

Refine hypothesis / Execute additional studies Implement control and prevention measures

Communicate findings


71/72

Communicate Findings The implicated seed lot was not distributed to any other

sprouting companies. The remaining 6,000 lbs. of seed was

immediately removed from the marketplace.

The Idaho Division of Food and Drugs held meetings at

which public health officials explained to seed growers the

need to protect alfalfa and other seeds used in sprouting fromcontamination during growing, harvesting, and packing.

Public television and radio announcements about the risk of

contaminated sprouting seeds, recommending persons at high

risk for complications fromE. coli O157:H7 not eat sprouts.

The Center for Food Safety and Quality Enhancement began

working with the sprout industry to identify ways to make

sprouts safer for human consumption.


72/72

Conclusions

Importance of applying the multi-step approach in

outbreak investigation

Utility of new subtyping methods such as PFGE

Importance of disease reporting

Flexibility of hypothesis generation

New vehicle for the transmission ofE. coli O157:H7

Increasing geographic dissemination of outbreaks

2009 Outbreak_Investigation.food Borne Ppt

Documents

Transcript of 2009 Outbreak_Investigation.food Borne Ppt