Case Finding and Line Listing: A Guide for Investigators

1. Case Finding and Line Listing: A Guide for Investigators

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. Information to Collect during Case Finding Process • Identifying • Demographic • Clinical • Risk factor

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. Example of a Line Listing 1=“Yes” ?=“Don’t know” 0=“No”

20. 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

21. 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.

22. References • Personal Communication of the FOCUS Workgroup with Dr. Pia MacDonald, 2003 • CDC. Epidemiologic Notes and Reports Eosinophilia-Myalgia Syndrome -- New Mexico. MMWR 1989; 38 (45): 765-767. • Maillard JM et al. First Case of Bioterrorism-Related Inhalational Anthrax, Florida, 2001: North Carolina Investigation. EID 2002; 8 (10): 1035-1038. • 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.

23. References • 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). • CDC. Summary of Notifiable Diseases-United States, 2001. MMWR 2003; 50 (53): 100-108. • 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. • CDC. Outbreaks of Multidrug-Resistant Salmonella Typhimurium Associated With Veterinary Facilities ---Idaho, Minnesota, and Washington, 1999. MMWR 2001; 50 (33): 701-4.