Foodborne Disease Outbreak
Investigation Team Training:
Module 2 – Foodborne
Disease Surveillance and
Outbreak Detection
Surveillance and outbreak detection
1
Module Learning Objectives
At the end of this module, you will be able to
1. Describe the surveillance of foodborne illness
through notification/complaint systems.
2. List ways to improve the accuracy of a food
history obtained in a foodborne illness complaint.
3. Describe the surveillance of foodborne illness
through pathogen-specific surveillance.
4. Recognize a possible outbreak using a
notification/complaint system or pathogenspecific surveillance.
5. Describe the role of local public health in
national pathogen-specific surveillance.
Surveillance and outbreak detection
2
Foodborne Disease Surveillance
• Many ways to find out about cases of
foodborne illnesses and outbreaks
• Two primary means
– Foodborne illness notification/complaint
systems
– Pathogen-specific surveillance (notifiable
disease reporting)
Surveillance and outbreak detection
3
Foodborne Illness
Notification/Complaint
Systems
Surveillance and outbreak detection
4
Notification/Complaint Systems
• Complaints of illness among individuals and
groups reported by affected members of the
community (and others)
• Includes any illness thought to be related to food
• Common exposures are used to link cases
together
Surveillance and outbreak detection > Notifications/complaints
5
Steps in Receiving Complaints
Illness in individual
or group
Complaint to local
health department

Starts with
complaint by
consumer
Interview of complainant
Documentation
of information
Evaluation of
individual reports
for immediate
action
Key information
entered into log
Routine review
of log
Common
exposures link
cases over time
Evaluation of
reports over time
for outbreaks
Surveillance and outbreak detection > Notifications/complaints
6
Interview of Complainant
Example in appendix

• Who is affected? (e.g.,
name, age, and sex)
• What is the problem? (e.g.,
symptoms, diagnosis)
• When did problem occur?
(e.g., date/time of onset)
• Where? (e.g., place of
residence and exposure)
• Why/how? (e.g., travel,
water, contact with ill
persons or animals,
suspect food or meal,
food history)
Surveillance and outbreak detection > Notifications/complaints
7
Collecting Food Histories
• Complete food history important including
– Foods eaten in 5 days before onset of illness
 If illness suggestive of norovirus, focus on
24-48 hours before illness.
 If >1 ill person, focus on shared foods/meals.
– ALL foods eaten during time period of interest
(unless focusing on shared foods/meals)
– Details of named events, food establishments,
or suspect food products
• Information on non-food exposures
Surveillance and outbreak detection > Notifications/complaints
8
Small Group Exercise
Divide into groups of two. One person will be the
interviewer; one will be the complainant.
1. The interviewer should solicit a 5-day food
history from the complainant.
2. The complainant should respond to questions as
if they just developed symptoms that day and
based on what they really ate in the last 5 days.
3. Was it easy or difficult? Did you get a complete
food history? What approaches were helpful?
Be prepared to share your
experience with the class.
Time: 10 minutes
Surveillance and outbreak detection
9
Improving Food Histories
Have complainant
•
•
•
•
•
•
•
•
Look at a calendar
Describe each meal in time period
Identify key events to jog memory
Review receipts or menus
Enlist help of dining partners
Consider specific list of foods
Think about food preferences
Rule out or rule in specific foods
Surveillance and outbreak detection > Notifications/complaints 10
Entering Information into Log
• Extract key information from the complaint to
facilitate examination of reports over time
− Date of illness onset
− Predominant signs and symptoms
− Name of food thought to have caused illness
− Names of eating places or gatherings
− Source of water and type
− Other exposures
• Transfer information carefully
• Use consistent abbreviations and codes
Surveillance and outbreak detection > Notifications/complaints 11
Evaluation of Complaints
Individual reports of concern:
• Symptoms suggestive of serious illnesses
• Laboratory-confirmed diagnoses
• Reports of obvious food safety problems
• Group illnesses thought to be due to an identified,
shared exposure
Surveillance and outbreak detection > Notifications/complaints 12
Group Illnesses Due to Identified,
Shared Exposure
Illnesses are likely to be related to an identified,
shared exposure (e.g. particular meal, event, or
establishment), if group members have:
• Similar signs and symptoms
• Shared a food or meal prior to onset of illness
and had no other common exposures
• Onset and nature of illness is consistent with
identified shared exposure
Surveillance and outbreak detection > Notifications/complaints 13
Class Question

Which of the following group illnesses are likely to be
due to the identified restaurant exposure?
Due to
Exposure
Person developed diarrhea after eating at
a restaurant. Neighbors who ate at the
restaurant also are sick but complainant
does not know their symptoms.
Four friends develop nausea and vomiting,
facial flushing, headache, and itching skin
within an hour of eating fish at a restaurant.
Family members develop bloody diarrhea
within hours of eating at a restaurant.
Surveillance and outbreak detection > Notifications/complaints 14
Evaluation of Complaints (cont’d)
Looking at reports over time
• Multiple individual complaints with same exposure
(e.g., same food establishment or food)
• Multiple individual complaints with clustering by
time, place, or person
• Overall increase in complaints
Surveillance and outbreak detection > Notifications/complaints 15
Response to Notifications/Complaints
• Notify epidemiology unit/communicable disease
staff of laboratory-confirmed diagnoses.
• Refer food safety problem to agency with
regulatory authority.
• Alert appropriate persons if possible outbreak
detected.
• Prioritize follow-up of
commercial establishments.
Surveillance and outbreak detection > Notifications/complaints 16
Follow-up of Commercial Establishments
Rational approach to follow-up
• As required by local law/statute or
• If complainant observed specific food safety
problem or
• If two or more persons (not from same household)
– Have similar illness
– Shared history of eating at
establishment
– Onset and nature of illness
consistent with shared foods
Surveillance and outbreak detection > Notifications/complaints 17
Group Exercise
Divide into groups by table. Study the foodborne
illness log at the end of this module spanning a 2week period and determine:
1. Is the number of complaints what you would
expect for the period covered?
2. Are there individual complaints of concern?
3. Are there common exposures (e.g. foods,
establishments) across complaints signaling an
outbreak?
Be prepared to share your
thoughts with the class.
Time: 10 minutes
Surveillance and outbreak detection
18
Strengths of Notification/Complaint Systems
Primary means to detect outbreaks that are
• Localized (involving only one jurisdiction)
• Due to diseases with a short incubation period
Surveillance and outbreak detection > Notifications/complaints 19
Notification/Complaint System Issues
•
•
•
•
Inaccurate and incomplete food histories
Large numbers of complaints
Anonymous complaints
Complaints with unknown causative agent
– Inability to exclude unrelated cases
– Inability to link cases based on illness unless
symptoms very unique or cases report
similar exposure
Surveillance and outbreak detection > Notifications/complaints 20
Pathogen-specific
Surveillance
Surveillance and outbreak detection
21
Pathogen-specific Surveillance
• Also called “reportable diseases,” “notifiable
diseases,” or “laboratory-based reporting”
• Reports of individual laboratory-confirmed cases
of foodborne disease by medical and laboratory
staff with submission of clinical isolates, where
requested
• Only covers diseases selected by
public health agency
• Cases linked to each other by
common pathogen
Surveillance and outbreak detection > Pathogen-specific
22
Steps in Pathogen-specific Surveillance 
Illness in individual
Individual seeks health care
Specimen collected
Common
pathogen links
cases over time
Follow-up
interview of
case
Diagnosis by health-care
provider/laboratory
Starts with
positive lab
result
Initial report to health
department
Submission of
isolate to
public health
laboratory
Entry into electronic
database
Further
characterization
Analysis of cases for
clusters/outbreaks
Forward to CDC
Surveillance and outbreak detection > Pathogen-specific
23
Initial Report
• From health-care
provider or laboratory
• Standardized form (often
pathogen-specific)
• Information of interest
− Patient identifiers
− Basic demographic
information
− Clinical information
− Laboratory results
Example in appendix
Surveillance and outbreak detection > Pathogen-specific
24
Follow-up Interview of Case
• To identify potential exposures leading to illness
• Similar to interview for notification/complaint
system but tailored to specific pathogen
− High-risk food exposures for agent
− Other exposures related to agent (e.g.,
contact with ill people, animals, water)
• Often occurs weeks after
exposure leading to illness
resulting in poor recall
Surveillance and outbreak detection > Pathogen-specific
25
Laboratory Characterization of Pathogen
• Submission of patient isolate to public health
laboratory for confirmation and subtyping
• Increased detail about the pathogen (e.g.,
serotyping, PFGE) improves
– Recognition of clusters
– Linking an outbreak with an exposure
• Most critical with common
pathogens
Surveillance and outbreak detection > Pathogen-specific
26
Analysis for Clusters
• Examine cases by pathogen over time using
– Different levels of specificity of pathogen (e.g.,
species, selected subtypes)
– Subgroups of population (certain time, place,
or person characteristics)
• Look for increase in number of cases over
expected or baseline, indicating
a cluster
Surveillance and outbreak detection > Pathogen-specific
27
Analysis by Causative Agent
Number of Case
Lab-confirmed salmonellosis cases by month of diagnosis,
2010.
All Salmonella
Month of Diagnosis
Surveillance and outbreak detection > Pathogen-specific
28
Analysis by Causative Agent Subtype
Number of Case
Lab-confirmed salmonellosis cases by month of diagnosis
All Salmonella
Salmonella Javiana
Month of Diagnosis
Surveillance and outbreak detection > Pathogen-specific
29
Analysis by Causative Agent and Age Group
Number of Cases
Lab-confirmed salmonellosis cases by month of diagnosis
All Salmonella
Salmonella Javiana among
persons <5 yrs.
Salmonella Javiana
Month of Diagnosis
Surveillance and outbreak detection > Pathogen-specific
30
Strengths of Pathogen-specific Surveillance
Primary means to detect outbreaks that are
• Wide-spread (i.e., multijurisdictional),
• Due to prolonged low-level food contamination, or
• Due to diseases with a long incubation (e.g.,
hepatitis A)
Surveillance and outbreak detection > Pathogen-specific
31
Pathogen-specific Surveillance Issues 
• Incomplete detection
and reporting
Reported
Culture-confirmed Case
Lab Tests for Organism
Specimen Obtained
Person Seeks Care
Person Becomes Ill
Population
Surveillance and outbreak detection > Pathogen-specific
32
Pathogen-specific Surveillance Issues 
• Incomplete detection
and reporting
• Elapsed time
Elapsed Time for Salmonella Reporting
Patient
eats food
Incubation period=1-3 d
Time to contact with health
care=1-5 d
Stool
sample
collected
Patient
becomes ill
Time to diagnosis=1-3 d
Shipping time=0-7 d Salmonella
identified
Isolates
received by Serotyping and PFGE=2-10 d
public
Case
health lab
confirmed
as part of
cluster
Surveillance and outbreak detection > Pathogen-specific
33
Pathogen-specific Surveillance Issues
• Incomplete detection
and reporting
• Elapsed time
• Availability of isolate for
further characterization
Surveillance and outbreak detection > Pathogen-specific
34
Comparison of Surveillance Systems
Notification/
complaint system
All
Pathogen-specific
surveillance
Types of foodborne
Only selected
illnesses detected
diseases
Initiating event
Consumer complaint Positive lab result
Means to link cases Common exposures
Same pathogen
Linkage of cases
Not usually
Yes
across jurisdictions
Exclusion of
Difficult
Good
unrelated cases
Speed
Fast
Relatively slow
Types of outbreaks Localized outbreaks; Widespread; lowbest detected
short incubation
level contamination
illnesses
events; long
incubation illnesses
Surveillance and outbreak detection
35
National Pathogen-Specific
Surveillance Systems
Surveillance and outbreak detection
36
National Pathogen-specific Surveillance
• NNDSS (National Notifiable Disease Surveillance
System)
− Data from pathogen-specific surveillance
forwarded to CDC (minimal case information)
− Statistical algorithm used to identify increases
• PulseNet (National Molecular Subtyping Network
for Foodborne Disease Surveillance)
− Laboratory network that uses standardized
pulsed field gel electrophoresis (PFGE) methods
− PFGE patterns uploaded by labs for STEC,
Salmonella, Shigella, Listeria, Campylobacter
− Comparisons of patterns to identify clusters
Surveillance and outbreak detection > National surveillance
37
National Pathogen-specific Surveillance
• CaliciNet (National Electronic Norovirus Outbreak
Network)
− Laboratory network that subtypes/sequences
norovirus isolates related to outbreaks
− Data uploaded to CDC allows linkage of
outbreaks and identification of new variants
• NARMS (National Antimicrobial Resistance
Monitoring System—enteric bacteria)
− Submission of Salmonella, Shigella, E. coli O157,
Campylobacter, and non-cholerae Vibrio to CDC
− Determines trends in antimicrobial resistance
Surveillance and outbreak detection > National surveillance
38
Role of Local Health Departments
• Local pathogen-specific case reports and
laboratory results feed into national surveillance
• Important for local health departments to
− Collect data in format consistent with other
investigators.
− Streamline reporting and isolate submission.
− Share case reports with state and submit
patient isolates to public health laboratory as
quickly as possible.
− Use national systems to learn about outbreaks
in other jurisdictions.
Surveillance and outbreak detection > National surveillance
39
What difference does one local case make?
• Two E. coli O157:H7 infections in MN with same
PFGE pattern; both ate tenderized steaks
• Through PulseNet, single cases identified in KS
and MI; both ate tenderized steaks
• Steaks eaten by cases
1
from same plant
6
1
1
• Recall of 739,000 lbs.
1
of beef
• Outbreak generated
high levels of concern
about needle/blade
tenderized steaks
Surveillance and outbreak detection > National surveillance
40
Quick Quiz
Surveillance and outbreak detection
41
Quick Quiz
1. Typically common exposures are used to
detect outbreaks through a foodborne illness
notification/complaint systems whereas a
common pathogen is used to detect outbreaks
through pathogen-specific surveillance systems
A. True
B. False
Surveillance and outbreak detection
42
Quick Quiz
2. Illnesses in a group are likely to be related to an
identified, shared exposure (e.g. particular meal,
event, or establishment), if group members have
which of the following?
A. Ill persons all have the same symptoms.
B. Ill persons shared food or a meal prior to
onset of illness and had no other common
exposures.
C. Onset of the illness is consistent with the
timing of the exposure.
D. All of the above
Surveillance and outbreak detection
43
Quick Quiz
3. Which of the following can improve the
accuracy of a food history solicited during a
foodborne illness complaint?
A. Have case look at a calendar and identify
key events to jog memory.
B. Have case review credit card or cash
register receipts to identify where or what
they ate.
C. Enlist help of dining partners.
D. All of the above
Surveillance and outbreak detection
44
Quick Quiz
4. All of the following are true of pathogen-specific
surveillance EXCEPT
A. Detects all types of foodborne illness.
B. Relies on reports from health-care providers
and clinical laboratory staff.
C. Is the primary means to detect widespread
outbreaks such as multistate outbreaks.
D. Has an inherent lag in reporting due to time
necessary to confirm pathogen through
laboratory testing.
Surveillance and outbreak detection
45
Quick Quiz
5. All of the following are important roles for local
health departments in national pathogenspecific surveillance EXCEPT
A. Collect information on local cases in a
format consistent with other investigators.
B. Share case reports with state health
department in a timely fashion.
C. Be alert to outbreaks in other jurisdictions.
D. Submit all patient isolates directly to CDC.
Surveillance and outbreak detection
46