Initial Case-Patient Interviewing


Interviewing case-patients about where and what they ate in the days or weeks before they got sick is a critical component to hypothesis generation during an outbreak investigation. Interviews can also identify high-risk case-patients who could spread their infections to others (e.g., food handlers, day care workers or attendees, healthcare workers). During interviews, case-patients can also receive information about risky exposures and how to protect themselves and others.

The FoodCORE Model Practice: Initial Case-patient Interviewing is intended to describe the basic practices and characteristics of conducting comprehensive interviews for all enteric disease case-patients upon initial identification or first contact, not just those identified as part of a local cluster or multistate cluster. The activities described would be applicable for various pathogens but are focused on those that are likely transmitted via food. Depending on jurisdictional resources, attempts should be made to interview all identified case -patients with enteric disease to ascertain an exposure history.

This model practice describes successful triage and routing of case reporting and the process of attempting interviews with case-patients, recommends categories and elements identified as essential to ascertain during an initial enteric disease interview, and provides a checklist to determine alignment of initial interview practices with the FoodCORE model practice.


Aligning with other initiatives

The initial interview model practice document is not intended to replace guidance about use of Listeria Initiative Case-patient Report Form or the Shiga toxin-producing Escherichia coli Standardized Case-patient Report Form (STEC Standard Form, under development).

The recommendations included in the initial interview model practice document align with the Core Elements defined within the Standardized National Hypothesis Generating Questionnaire (SNHGQ). The SNHGQ defines the minimum recommended elements to be used in interviewing case-patients known to be associated with a multistate cluster investigation. The SNHGQ elements should be an equivalent or expanded version of initial interviews that are not associated with a multistate cluster investigation.

Case-patient identification

Case-patients of enteric disease are identified using a variety of sources, including laboratory reporting, direct reports from other jurisdictions or agencies (other states, CDC, etc.), and consumer complaint systems. Identified case-patients with a reasonable expectation of being an enteric illness should be investigated. If a complaint system is available, data should be reviewed to identify potential clusters or trends.

FoodCORE centers utilize various electronic systems to track reported case-patients, completed interviews, and to store demographic and exposure data centrally for ease of review and analysis.

Timeliness, timing, and description of interview attempts

Interviews should be attempted as soon as possible after public health officials are notified of a case-patient, which may be before all subtyping is completed. Prompt interviewing is critical for best exposure recall by the case-patient and increases the likelihood of identifying epidemiologic links between cases and food products that may be available for testing. Additionally, early interviewing provides an opportunity to give prompt prevention education to case-patients to limit secondary transmission, especially if they have a connection to a high-risk setting (e.g., food workers, childcare workers or attendees, or healthcare workers).

At least three attempts should be made to contact each case-patient. Attempts should be made at different times of day, with at least one attempt during evening or weekend hours, if possible.

During initial contact, interviewers can determine if the interview would be better conducted at a different time, confirm case-patient contact information, and arrange for the interview to be conducted with an interpreter or other means of translation service, if necessary, and if resources are available.

If a case-patient cannot be reached for interview via telephone, FoodCORE centers have used the following approaches to attempt to ascertain exposure history and/or conduct prevention education:

Before sending a text message, some FoodCORE sites use software to determine if the phone number they have for a case-patient is for a cell phone. Other sites send a text message to any phone number without first validating.

  • Leave a voicemail and/or send a text message to case-patients with call back information, either a toll-free or direct line for reaching an interviewer. FoodCORE centers have used ELC funds to purchase cell phones in order to leave text messages.
  • Mail a letter from the relevant public health agency with the reason for attempted contact and provide both contact information and educational prevention materials about the enteric pathogen. This letter may also contain a paper copy of the questionnaire for the case-patient to fill out and mail back in a stamped and addressed envelope. See Appendix C Cdc-pdf[PDF – 149 KB] for sample letters.
  • Though not used for all routine interviews, some centers provide online questionnaires for exposure ascertainment. This method of exposure ascertainment is used as an alternative method for case-patients who cannot be reached via traditional methods or are unwilling to complete an interview over the phone but would like to provide their exposure history online. Online systems for self-reported data must be secure and allow for confidential data submission.

Interview content

FoodCORE initial case-patient interviews include elements from the following major categories:

  • Demographics
  • Clinical History
  • Travel
  • Risks to others
  • Local Cluster/Events, Finding Additional Cases
  • Food Sources/Diet Information
  • Other Exposures (animal, water, environmental, etc.)

Please see Appendix A Cdc-pdf[PDF – 53.1 KB] for the table of minimum suggested elements within each major category.

For all case-patients of enteric disease, data collected in categories 1-5 are needed to identify case-patients where public health officials can provide educational information to prevent additional illnesses and to identify any events or local trends that could indicate ongoing risk. FoodCORE center initial interviews include elements in categories 6 and 7 as part of a full exposure history.  Depending on jurisdictional resources, interviews should collect sufficient detail to enable public health investigation in these categories. As resources allow, jurisdictions can evaluate including a detailed food exposure history as part of an initial interview. Other initiatives, including the Listeria Initiative, the STEC Standard Form, and the SNHGQ,  have suggested food categories and elements to ascertain in a food history (e.g., Meat and Poultry; Fish and Seafood; Eggs, Dairy, and Cheese; Fruits and Vegetables; Frozen and Convenience Foods).

For successful interviews, interviewers should be familiar with the questionnaire and jurisdictional policies for education and intervention so the case-patient interaction is efficient and comfortable. The content and structure of the initial interview should be understandable, and sensitive to the personal nature of the questions. FoodCORE centers have implemented the following practices and considerations:

  • The order in which elements are asked can influence how responsive a case-patient may be
    • More sensitive information should be collected after the case-patient is comfortable with the interviewer and the reason for being contacted
  • If an interviewer determines that a case-patient is short on time, elements can be prioritized to ascertain the highest priority elements earlier in the interview
    • This could include risk of spreading infection to others or identifying additional case-patients for local clusters/events
  • Interview elements can also be prioritized for pathogen-specific concerns to focus on highest priority elements for those specific interviews
    • This should include identifying persons who are at risk of spreading infection to others
  • Since interviews may be conducted before case-patients are linked to a cluster of illness, interviewers may explain to case-patients that they may be re-contacted for additional details about their illness to keep other people from getting sick
    • Interviewers can verify contact information and preferred means of contact, the best times of day to reach a case-patient, and other preferences (as reasonable), such as preferred language