Case interviewing

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A case interview is an interaction between an outbreak interviewer and a case (or proxy) or other persons involved in the outbreak (e.g., food handlers, managers of a restaurant). Determining who should be interviewed is informed by the case definitions and the specifics of the outbreak. The primary role of an interviewer is to build a relationship, gather information, and provide education.  The information gathered during an interview can inform the food safety investigation and prevention and control measures.

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Interview logistics

Interviews may be conducted by a single or multiple interviewers. Factors such as the investigation objectives and available resources will help inform the approach that will be used. The table below summarizes some of the advantages and disadvantages of having single versus multiple interviewers.

  Single interviewer Multiple interviewers
  • Increased ability to detect patterns/similarities among cases
  • Data comparable across cases
  • Easier to oversee and ensure interviews are done in a relatively standardized fashion
  • Easier to ensure content reflects most current information from previous cases
  • Many people thinking about source (different perspectives)
  • Faster, useful when there are many cases in different jurisdictions
  • Fewer people thinking about source (only one perspective)
  • Much less efficient time-wise
  • May miss common patterns or similarities among cases
  • Difficult to ensure consistent questioning and content
  • Ties up resources

Regardless of the number of interviewers, training is an essential part of successful case interviews to ensure that the information gathered will be useful for the outbreak investigation. Training could cover skills and knowledge such as:

  • Understanding the intent of the interview and general structure of the questionnaire (layout, skip patterns),
  • Knowing the appropriate information and advice that can be shared with the case (e.g., an epidemiologist or analyst will likely not be able to provide the same level of health advice as a public health nurse),
  • Improving interviewing techniques such as facilitating case recall and probing cases to provide more detail without introducing biases,
  • Understanding the documentation/data management expectations (e.g., recording responses in the appropriate format).

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Preparing for an interview

The primary role of an interviewer is to build a relationship, gather information, and provide education.

Building a relationship

The key to a successful interview begins with establishing a positive relationship with the case. Holding the interview in a quiet environment with minimal distractions and interruptions will help ensure that this interaction is positive. If possible, gather a history of interactions the case has already had with public health and make sure you have the information they have already provided readily available so you can verify information rather than re-asking questions. The case may be unaware of his or her diagnosis and may not have heard of, or spoken to, public health before. In this case, you need to be prepared to explain who you represent and why you are calling. On the other hand, the case may have already had extensive interaction with public health, in which case you need to explain why multiple calls and interviews are necessary.

Information gathering

Gathering information is one of the main goals of the case interview during outbreak investigations. Be sure you understand the tool or questionnaire that is being used to collect information. Be conscious of how the questionnaire is designed and consider preparing transition statements in advance that you can use to guide the case through the process. Understand what the questions are asking and be able to pronounce all words and describe all food exposures.

Recall can be challenging for cases, particularly for foodborne outbreak investigations where cases may be asked to describe foods they ate several weeks ago. Referring to a calendar and noting important events (e.g., holidays, sporting events, and specific weekly or daily activities) may help trigger the case’s recall. Pictures or other visual triggers such as menus and maps, as well as records such as receipts or banking information, can all assist recall.

Overall, maintain a flexible approach with how you work with your case to gather information. For example, some cases may prefer to work forward in time to illness, whereas others may prefer to work backwards from illness.

Educating respondents

The case interview is an excellent opportunity to provide education and should not be overlooked due to time constraints, communication barriers, or uncomfortable topics. Your messaging (e.g., hand hygiene recommendations) should align with your organizational policies and recommendations and should be tailored to the personal situation. The advice and recommendations you are able to provide may vary depending on the situation and should be aligned with what is appropriate within your jurisdiction given your position (e.g., physician, nurse, epidemiologist, public health inspector). Be sure to clarify the rules and expectations prior to beginning your interview. It may be helpful to assemble references that may help you during the interview such as disease-specific fact sheets, websites, and other references (e.g., Control of Communicable Diseases Manual). It is also useful to be aware of what the case may be aware of already and what questions are likely to come up, for example, for outbreaks that have received significant media attention. 

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Parts of an interview


An interview begins with an introduction. Take the time to explain who you are (e.g., name, position, and organization) and why you are calling and/or conducting an interview. Clearly state why the case should participate and that he or she does not need to provide an answer to any of the questions asked. It is also helpful to provide the case with an indication of the length and the structure of the interview. In some instances, a script may be included with the questionnaire so that interviewers can introduce, guide, and conclude the interview in a consistent manner.

The issue of confidentiality and a discussion about how the data will be used is important.  In most jurisdictions, if the individual agrees to the interview after you have completed the introduction, this is considered informed consent. Consider clarifying the rules and obligations regarding privacy and consent in your jurisdiction prior to beginning your interviews.

Common challenges

During the interview, there may be a number of challenges that arise that may affect your ability to engage in a meaningful relationship with your case and gather the necessary information. While these situations may make the interview more challenging, there are some strategies you can consider while you gauge how to continue and how it will affect the rest of the interview.

In some instances, for example, leaving the topic and moving on may be the best option (e.g., case does not want to discuss their illness and the most important information you need is food exposure history – pressing too much on the details of the illness may compromise your ability to capture food exposure data).

Strategies related to elaborating, asking for examples, explaining or specifying are intended to elicit information in an ambiguous manner and thereby decreasing bias. This technique involves asking more specific questions about previously stated information and rather than introducing a new topic or a new line of questioning. This is particularly useful when the answer is not clear, or when the case does not seem to understand the question.

Challenge Strategy Example
Refuse / reluctant to answer Leave/delay an issue We can move onto the next question
We can come back to this later
Insufficient detail Elaborate Can you tell me a little more about that?
Response unclear Exemplify Can you give me an example of that?
Explain I’m not sure I got all of that. Can you explain one more time?
Gets off topic Specify Please be more specific about ___________
Response unclear Re-state So you said _________, is that correct?
Contradictory answers
Uncomfortable with sensitive questions Re-iterate purpose The information is used to _______________
It’s important I ask these questions because __________
Demanding answers/action (e.g., compensation for lost time at work) Address concern Validate concern, answer honestly, refer them to additional resources
Angry with the experience/process


At the end of the interview, thank your case for taking the time to talk to you and for contributing to the investigation. Provide an opportunity for the case to add any additional information or to ask questions before you end the interview. As cases may recall information relevant to the investigation or have additional questions later, it is useful to provide your contact information (or clinic information) where you may be reached. As cases are often contacted multiple times throughout an outbreak investigation, it is good practice to inform cases that they may be contacted again.


As the goal of the interview is to gather information for outbreak investigation purposes, the data you collect is critical for the investigation. How the data are managed will have a significant impact on the ability to use the information to support public health action. Clear documented responses will enable those analyzing the data from the interview to understand what was gathered from the interview and avoid ambiguity (e.g., a blank response for a question may carry different meanings, such as the question was not asked, or the respondent did not have a response or it was unknown, etc.). Consider reviewing your notes and the questionnaire after the interview to ensure that they are complete, legible, and accurately reflect the information gathered during the interview.

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Toolkit enteric questionnaire repository

  • This repository contains questionnaires for various pathogens, to be used at various stages of an outbreak investigation, including hypothesis generation, refinement, and testing.

Interview Script Examples

  • This Microsoft Word document provides interview script examples for initiating and concluding case interviews.

CDC Effective TB Interviewing for Contact Investigation

  • This TB interviewing module is a self-study tool for contact investigation. This resource offers guidance on communicating clearly with patients under different circumstances and is intended for both new and experienced TB interviewers.

Oregon Public Health Division Interviewing Cardinal Rules

  • This video explains the 10 cardinal rules of effective interviewing. The longer version contains more background and is very helpful for understanding outbreak investigation interviewing. The shorter 9-minute version is useful as a quick introduction to interviewers, for times when it is important to get on the phones as quickly as possible.

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