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/SymptomsLabsDemographics Case # Date of Symptom Onset DiarrheaVomitingFever >101 Positive stool culture AgeGender 11/2/0411?119M 21/5/ M 31/2/ F 41/7/ ? 51/1/04?11118F

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.

References 1.Personal Communication of the FOCUS Workgroup with Dr. Pia MacDonald, CDC. Epidemiologic Notes and Reports Eosinophilia-Myalgia Syndrome -- New Mexico. MMWR 1989; 38 (45): Maillard JM et al. First Case of Bioterrorism-Related Inhalational Anthrax, Florida, 2001: North Carolina Investigation. EID 2002; 8 (10): 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:

References 5.CDC. EXCITE: Epidemiology in the Classroom. How to Investigate an Outbreak: Steps of an Outbreak Investigation, ( 6.CDC. Summary of Notifiable Diseases-United States, MMWR 2003; 50 (53): 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): CDC. Outbreaks of Multidrug-Resistant Salmonella Typhimurium Associated With Veterinary Facilities ---Idaho, Minnesota, and Washington, MMWR 2001; 50 (33):