Basics of Study Design in Foodborne Illness Outbreak Investigations Instructor Name Job Title Organization

Types of outbreak activities …and lots and lots of talking to people! Laboratory Environmental Epidemiology

Foodborne outbreak definition A foodborne disease outbreak is defined as an incident in which two or more persons experience a similar illness resulting from the ingestion of a common food CDC definition

How are outbreaks detected? Notification/complaints systems  Independent complaints  Reports of a group of ill persons Pathogen-specific surveillance  Case reporting by laboratories

Recent outbreak examples [Instructor, add local examples that match those you created in the Presentation PowerPoint] […Outbreak of listeriosis linked to cantaloupes (2011)—146 people ill and 30 deaths from 28 states…] […Gastrointestinal outbreak at a prison—45 cases (2013) …] […E. coli O157 outbreak linked to cucumbers served at Denver Metro sandwich shop (2013)—9 people ill…] […Campylobacter raw milk outbreak in Gunnison, CO (2013)— 34 cases…] […Multistate outbreak of Salmonella associated with ground beef (2014)—12 Colorado cases…]

Two outbreak scenarios Traditional (focal) scenario: Acute local outbreak Detected by group themselves High dose, high attack rate Local investigations Often a local food handling error Local solution New (widespread) scenario: Diffuse widespread outbreak Detected by lab-based subtype surveillance Low dose Low attack rate Increase in "sporadic" cases Industrial contamination event Industry-wide implications

General characteristics Traditional (focal) outbreaks May or may not know pathogen involved Most ill people have not visited the doctor Can define a group of people who were potentially exposed o e.g., wedding, classroom, event attendee Some idea of the types of activities these people had in common

General characteristics Widespread (newer) outbreaks Pathogen is known Cases generally dispersed over several counties or states Investigation may be less timely At outset, probably have no idea what cases have in common After extensive case interviewing, may have a few hypotheses about exposure to test

Recent outbreak examples [Instructor, add local examples that match those you created in the Presentation PowerPoint] […Outbreak of listeriosis linked to cantaloupes (2011)—146 people ill and 30 deaths from 28 states…] […Gastrointestinal outbreak at a prison—45 cases (2013) …] […E. coli O157 outbreak linked to cucumbers served at Denver Metro sandwich shop (2013)—9 people ill…] […Campylobacter raw milk outbreak in Gunnison, CO (2013)— 34 cases…] […Multistate outbreak of Salmonella associated with ground beef (2014)—12 Colorado cases…]

Recent outbreak examples [Instructor, add local examples that match those you created in the Presentation PowerPoint] […Outbreak of listeriosis linked to cantaloupes (2011)—146 people ill and 30 deaths from 28 states…] […Gastrointestinal outbreak at a prison—45 cases (2013) …] […E. coli O157 outbreak linked to cucumbers served at Denver Metro sandwich shop (2013)—9 people ill…] […Campylobacter raw milk outbreak in Gunnison, CO (2013)— 34 cases…] […Multistate outbreak of Salmonella associated with ground beef (2014)—12 Colorado cases…]

Cohort study—mechanics Attempt to interview entire group (or random sample), regardless of illness status ‒ e.g., Wedding attendees, school class, event attendees Use same questionnaire used for everyone in the group (ill and well) Questionnaire based on known activities/foods that group members may have done or eaten  Created from menus, early interviews etc. Includes questions about ‘unknown’ exposures  “Did you do anything else that I forgot to ask about?”

Cohort study—analysis Calculate attack rates an relative risks (RR) RR = Incidence rate (exposed) versus Incidence rate (unexposed) ‒ e.g., 85% of those who ate ham became ill compared with 10% of those who did not eat ham; 85/10 = Relative risk of 8.5 Cohort study Exposed IllWell Not exposed Ill Well

Interviewing for cohort studies Advantages : Easier to locate people for interview (have names, phone #s) Participants often motivated because connected to outbreak They might be expecting your call Shorter, more focused questionnaire Events are often relatively recent so recall may be good Participants may offer information about additional exposures of which you were not aware Challenges: Interviewees ask lots of questions Worried about becoming ill Sometimes are angry about having been exposed Interviewer must spend more time reassuring, answering questions, etc. Must be careful about confidentiality when interviewees ask about other who are ill

Case-control study—mechanics Define a ‘case’ based on laboratory criteria (with restrictions by time, place and person) Interview all cases (may be their 3 rd or 4 th interview!) Need to identify potential controls ‒ People who had opportunity to be exposed and become ill ‒ Age, sex, geographic matching is common Controls may be identified using ‒ Random or sequential digit dialing, anchored on case’s # ‒ Neighborhood controls (same neighborhood as case) ‒ Restaurant reservation lists ‒ Other creative methods (depending on outbreak)

Case-control study—mechanics Questionnaire asks same questions about exposure for cases & controls Because of matching often need to ask questions about age, sex, location up front Often exclude persons ill during outbreak period; therefore need to ask symptom questions upfront Need to define exposure period you are asking about for controls ‒ Might be several weeks in the past

Case-control study—analysis Odds of exposure (cases) versus Odds of exposure (controls)  Odd ratio (not direct assessment of risk)  Calculation complicated by adjust for matching on age, sex, or other factors Case- control Ill (Case) Exposed Not exposed Well (Control) Exposed Not exposed

Interviewing for case-control studies Advantages: Fewer total people needed for interview Not based on cooperation of group leader to provide ‘the list’ Challenges: Lots of work to identify potential controls Must apply inclusion/exclusion criteria (age, sex, screen for illness, etc.) Cold calling results in hang ups and rude answers ‘How did you get my number?’ Longer, less-focused questionnaire Time frame for questionnaire might be several weeks in past

Goals for all study types Complete, detailed information from all who are interviewed Describe the illness among ill people (cases) Identify foods or other exposures associated with illness in a timely fashion Implement control measures now or in the future … All begins with a good interview!