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Case Finding and Line Listing:
A Guide for Investigators
Goals

The goals of this presentation are to
discuss:
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the importance of case finding and line listing
strategies to identify cases and common
challenges during the process
how to collect and use the information
gathered
the creation and management of a line listing
Why is Case Finding
Important?
In an outbreak:
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There are usually more cases than are
reported to the health department
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Reported cases may not be representative of all
cases
To identify exposure and/or outcome
investigator needs information from
persons who represent all cases
Example-Blastomycosis
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2001 North Carolina outbreak of human
and canine pulmonary blastomycosis
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Was first identified in four students at a
small town school
School was undergoing construction,
construction had been associated with past
blastomycosis outbreaks
Example-Blastomycosis
However…
 Case finding revealed four additional
human cases and four canine cases
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None of which were associated with the
school
Case finding prevented incorrect
conclusion and intervention
Why is Case Finding
Important?
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To refine the case definition as more
information is garnered
To allocate resources
To define the exposed population for
the purposes of developing control
measures
How to Find Cases
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Cast a wide net at the beginning of an
investigation
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Active strategies involve soliciting health
facilities and/or laboratories
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Examples: visiting a local ED to review patient
records, asking clinicians to request labs from
patients who meet clinical case definitions,
screening an exposed population
How to Find Cases
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Passive strategies involve review of
information provided to you
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Examples: reviewing county surveillance
data
Cases may be found with both
strategies, but in an outbreak it is
imperative to use active case finding
methods
More Examples of Active Case
Finding
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Querying local TV, radio or newspapers
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Utilizing unconventional sources
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May be appropriate especially if outbreak involves
contaminated food item or potential bioterrorism
Wedding invitation lists, guest books, credit card
receipts
Asking each person
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Appropriate if outbreak occurred in a defined
population, such as a cruise ship
Common Challenges to Case
Finding
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Even when active case finding is
performed, it is unlikely that all cases
will be identified
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Not all specimens are routinely tested for
certain pathogens
Some infected persons may not seek
medical attention
The exposed population may not be well
defined
Information to Collect during
Case Finding Process
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Identifying
Demographic
Clinical
Risk factor
Information to Collect during
Case Finding Process
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Examples of identifying information to
collect
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Name, address, phone number, date of
birth
Confidentiality is very important
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Consider using a case ID
Information to Collect during
Case Finding Process
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Examples of demographic information
to collect
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Age, gender, race, occupation, recent travel
Examples of clinical information to
collect

Symptoms, date of onset, lab results,
severity of illness
Information to Collect during
Case Finding Process
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Examples of risk factor information to
collect
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Varies by type of outbreak

For example, in an outbreak of E. coli 0157:H7
information about beef consumption should be
asked
What is a Line Listing and
Why is it Important?
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It provides organized information about
the cases in an outbreak
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Information about person, place and time
that is obtained from case finding efforts
Can be quickly reviewed and updated
How to Create a Line Listing
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Can create electronic or paper version
Can use software such as Microsoft
Excel or Access, EpiInfo
Create a table in which each row
represents a case and each column
represents a variable of interest
How to Create a Line Listing
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Add new cases as the are identified
Update case information throughout the
investigation
Number of variables to include will vary
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Fewer will allow for quick visual
assessment
More will be useful for assessment and
characterization of outbreak
How to Create a Line Listing
Always include:
 Components of case definition
 Case name or identifying number
 Date of symptom onset (or specimen
collection date)
May also include additional information such as:
 Age, gender, race, occupation, risk factors
Example of a Line Listing
Signs/Symptoms
Labs
Case Date of
#
Symptom
Onset
Diarrhea Vomiting
Fever
>101
1
1/2/04
1
1
?
1
19
M
2
1/5/04
0
1
0
0
17
M
3
1/2/04
0
1
0
1
23
F
4
1/7/04
1
1
1
1
18
?
5
1/1/04
?
1
1
1
18
F
1=“Yes”
0=“No”
?=“Don’t know”
Positive
stool
culture
Demographics
Age
Gender
Using Information from a Line
Listing
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Frequency distributions of demographics
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Frequency distributions of potential exposures
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May provide information about exposure and/or
risk of disease
May provide information about source or route of
transmission
Spot maps/GIS
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May provide information about exposure patterns
Conclusion
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Finding cases and creating a line listing
are two crucial parts of any outbreak
investigation.
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Finding cases is necessary to characterize
the outbreak as accurately as possible
A line listing is a useful tool that enables
the investigator to quickly summarize,
visualize and analyze the key components
of the outbreak.
References
1. Personal Communication of the FOCUS Workgroup with Dr. Pia
MacDonald, 2003
2. CDC. Epidemiologic Notes and Reports Eosinophilia-Myalgia
Syndrome -- New Mexico. MMWR 1989; 38 (45): 765-767.
3. Maillard JM et al. First Case of Bioterrorism-Related Inhalational
Anthrax, Florida, 2001: North Carolina Investigation. EID 2002;
8 (10): 1035-1038.
4. Dwyer DM and Groves C. Outbreak Epidemiology. In: Nelson
KE, Masters Williams C, Graham NMH, eds. Infectious Disease
Epidemiology: Theory and Practice. Gaithersburg, MD: Aspen
Publishers, 2001: 119-148.
References
5. CDC. EXCITE: Epidemiology in the Classroom. How to Investigate
an Outbreak: Steps of an Outbreak Investigation, 2002.
(www.cdc.gov/excite/classroom/outbreak_steps.htm#step6).
6. CDC. Summary of Notifiable Diseases-United States, 2001. MMWR
2003; 50 (53): 100-108.
7. Breuer T, Benkel DH, Shapiro RL et al. A Multistate Outbreak of
Escherichia coli 0157:H7 Infections Linked to Alfalfa Sprouts Grown
from Contaminated Seeds. Emerging Infectious Diseases 2001 ;7
(6): 997-982.
8. CDC. Outbreaks of Multidrug-Resistant Salmonella Typhimurium
Associated With Veterinary Facilities ---Idaho, Minnesota, and
Washington, 1999. MMWR 2001; 50 (33): 701-4.