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Case Finding and Line Listing: A Guide for Investigators
Goals The goals of this presentation are to
discuss: 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: There are usually more cases than
are reported to the health department 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
2001 North Carolina outbreak of human and canine pulmonary blastomycosis 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 None of which were associated with
the school Case finding prevented incorrect
conclusion and intervention
Why is Case Finding Important?
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
Cast a wide net at the beginning of an investigation Active strategies involve soliciting
health facilities and/or laboratories 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
Passive strategies involve review of information provided to you 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
Querying local TV, radio or newspapers May be appropriate especially if outbreak
involves contaminated food item or potential bioterrorism
Utilizing unconventional sources Wedding invitation lists, guest books, credit
card receipts Asking each person
Appropriate if outbreak occurred in a defined population, such as a cruise ship
Common Challenges to Case Finding
Even when active case finding is performed, it is unlikely that all cases will be identified 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
Identifying Demographic Clinical Risk factor
Information to Collect during Case Finding
Process
Examples of identifying information to collect Name, address, phone number, date
of birth Confidentiality is very important
Consider using a case ID
Information to Collect during Case Finding
Process
Examples of demographic information to collect 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
Examples of risk factor information to collect 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?
It provides organized information about the cases in an outbreak 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
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
Add new cases as the are identified Update case information throughout
the investigation Number of variables to include will
vary 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
1=“Yes” ?=“Don’t know”
0=“No”
Signs/Symptoms Labs Demographics
Case #
Date of Sympto
mOnset
Diarrhea
Vomiting
Fever >101
Positive stool
culture
Age Gender
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
Using Information from a Line Listing
Frequency distributions of demographics May provide information about exposure and/or
risk of disease Frequency distributions of potential
exposures May provide information about source or route
of transmission Spot maps/GIS
May provide information about exposure patterns
Conclusion Finding cases and creating a line
listing are two crucial parts of any outbreak investigation. 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.
References1. 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.
References5. 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.