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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


Process

Examples of identifying information to collect Name, address, phone number, date

of birth Confidentiality is very important

Consider using a case ID


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


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


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


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.