Outbreak Alert - Shigella
Students will analyze a real-life foodborne illness outbreak. They will assume the role of FBI (FoodBorne Illness) investigators to plot out the steps and identify the questions to ask in order to get to the source of the outbreak. Students will discuss and compare their investigative approaches to the actual public health investigation. Grades 6-8
- Food safety portfolios (for each student)
- Dr. X and the Quest for Food Safety video, Module 5 — Outbreak and Future Technology
- For background information on outbreaks, read about the following in the Food Safety A to Z Reference Guide:
- Pulse-Field Gel Electrophoresis
- PulseNet (also see the step-by-step process for tracing a food implicated in a foodborne illness outbreak)
- Make one copy of the attached, Here’s What the Public Health Officials Did handout for each team.
Essential File (map, chart, picture, or document)
shigella: a bacteria closely related to salmonella that can cause foodborne illness
Background Agricultural Connections
Although our food supply is one of the safest in the world, foodborne illness outbreaks do occur. It’s important to be aware of the symptoms of foodborne illness and see a doctor if symptoms are severe. If the local clinical lab identifies the presence of foodborne bacteria in a patient’s test, the results are sent to the state health department for further testing. When outbreaks do occur, there’s a national network of public health laboratories, such as PulseNet, that helps to detect an outbreak in multiple states.
Even though our food supply is the safest in the world, we face new challenges as we import food from all over the world, as new pathogens emerge, and as familiar ones grow resistant to treatment. Foods reaching your table today are produced, processed, and distributed very differently than they were just a decade ago. Food from a single source may be rapidly distributed to communities across the nation, which could make it more difficult to detect a disease outbreak caused by contaminated food … but just as food can now be rapidly distributed, developments in technology are allowing us to keep track of foodborne outbreaks across the United States more quickly and easily.
Using molecular technology and a sophisticated computer system, epidemiologists can now rapidly assess whether a widespread food incident is underway, and they can trace the source of the problem by identifying distinctive fingerprint patterns of pathogens like E. coli O157:H7.
PulseNet is a way scientists are able to link microorganisms from different places associated with an outbreak to see if they have a common origin. Local laboratories participating in PulseNet perform DNA fingerprinting on bacteria that have caused illness. Microbiologists extract DNA from the microorganism and then pulse an electrical current through that material. The pattern, or fingerprints, received by the currents is then transmitted through a networked computer system to the Centers for Disease Control and Prevention (CDC).
If patterns submitted by laboratories in different locations match, CDC computers will alert PulseNet participants of a possible multi-state outbreak. An investigation can begin immediately to trace the source of the problem and stop the outbreak. If the source is found, the food will be taken off the market and measures will be taken to prevent future outbreaks.
Science and our Food Supply
This lesson was developed as a portion of an entire unit of lessons focusing on food safety from farm to table. Use the following links to see the remaining lessons:
Module 1: Bacteria
Module 2: Farm
Module 3: Processing and Transportation
Module 4: Retail and Home
- Supermarket Smarts
- Cooking Right: The Science of Cooking a Hamburger
- A Chilling Investigation
- Crossed Up!
- Hands Off, Bacteria!
Module 5: Outbreak and Future Technology
- Outbreak Alert - Shigella
- Beef Blasters
Evaluation: Lose a Million Bacteria (The Game)
Interest Approach - Engagement
- Motivate your students with this scenario: You’re sitting in your office. All of a sudden, red lights are flashing! You hear, “ring,” “ring,” “ring” all around you. What’s going on? Then finally you realize that this flutter of red lights and constant ringing is your telephone — it’s ringing off the hook. Could it be . . . an outbreak?
- Continue to engage the students by telling them that they are FBI (FoodBorne Illness) investigators in Suffolk County, New York. They’ve just received notice that 21 people in the county have become ill with similar symptoms (nausea, vomiting, diarrhea, cramps, and fever). The illnesses occurred over a 1-month period — from November 8 to December 8. The sick persons have tested positive for the Shigella bacterium. Ask, "How would you investigate this case to find out how the outbreak got started?"
- Divide the students into 3 or 4 groups.
- Inform students that as FBI (FoodBorne Illness) investigators, it’s their job to work with their colleagues to identify the steps they would take to investigate this outbreak.
- Ask students, "What do you know about this case?" Have them analyze the existing data and record it in their food safety portfolio in the form of the 5 “Ws” (“Who,” “What,” “Where,” “When,” and “Why,” plus “How”). Note: 4 of the “Ws” were given in the Interest Approach activity.
- Who – 21 people who became ill
- What – Shigella bacterium
- Where – Suffolk County, New York
- When – November 8 to December 8
- Why – ?
- Challenge each team to discover more details about the case. They should come up with more specifics on each “W,” then solve the “Why” and “How” of this case. For example:
- What is Shigella?
- How is Shigella transmitted?
- Where in Suffolk County could this outbreak have occurred?
- Ask students, "What do you need to find out first?" To help them along the way, students can conduct research about outbreaks and Shigella (Refer students to the websites listed below). From time to time, you can also give them clues (see box at right for clues and the answers), but first allow the students to formulate their own strategies.
- Alphabetical Listing of Foodborne, Waterborne, and Environmental Diseases and Links
- CDC Food Safety Initiative
- Foodborne Illnesses: What You Need to Know/FDA
- Foodborne Illnesses: What You Should Know About Government Response to Foodborne Illness Outbreaks/FDA
- Food Recalls and Alerts
- Pathogen Tracker Game/Cornell University
- PulseNet - The National Molecular Subtyping Network for Foodborne Illness Surveillance/CDC
- USDA Food Recalls
- Have the teams write up their steps. Make sure they number each step.
- Then, have each group share their investigation steps and their conclusions with the class.
- Discuss and compile a class list of what would be the most probable conclusions as to where the outbreak occurred, who or what transmitted the Shigella bacterium, and why the outbreak occurred. Then ask, "What would you do to correct the problem?"
- After you have compiled the class list, review the real-life, step-by-step process that Public Health Officials in Suffolk County, New York, conducted (see attachment in Essential Files). Compare the class approach and conclusions with the actual investigation. Are there similarities? Differences?
- Note: It’s okay if the students do not come up with the exact steps or conclusions as the actual investigation. The important thing is for them to arrive at a conclusion that’s based on logical, scientific questioning and a step-by-step process.
- Now it’s time to meet scientists who will share some of the tools they have for investigating FBI outbreaks. Watch for what they have to say about:
- The connection between PulseNet and DNA
- Pulse-Field Gel Electrophoresis (PFGE)
- How the Internet aids in outbreak investigations
- Show video Module 5 — Outbreak and Future Technology. Stop the video right after Dr. Paul’s segment (Time: 3 minutes). The rest of the video module is shown at the end of the Beef Blasters activity.
Concept Elaboration and Evaluation
Use the following questions to review and summarize the lesson:
- How could this outbreak have been prevented? (The restaurant manager should not have come to work if he was sick. The appropriate handwashing supplies should have been provided in the kitchen and employee and customer restrooms. The manager should have washed his hands properly.)
- Why is it important for public health officials to investigate foodborne illness outbreaks? (Early detection of an outbreak helps determine the possible source of that outbreak and prevents additional people from getting sick or dying from consuming harmful foodborne bacteria. Also, what public health officials learn from these outbreaks can help prevent future outbreaks.)
- Why is it important to wash hands even when you don’t feel sick? (Even though you may not feel sick, you could be a carrier of a foodborne bacterium without experiencing the symptoms. Therefore, if you don’t properly wash your hands, you could spread the bacterium from your hands to foods. For example, the store manager in the Shigella outbreak was a carrier of the bacterium when the French fries were contaminated, but he didn’t experience the symptoms until several days later. Proper handwashing is of extreme importance at all times.)
- What can you do to make sure your food is safe when you eat at fast-food restaurants? (When you go out to eat, always wash your hands properly before eating food. Also, observe the restaurant’s surroundings. If it’s not up to your cleanliness standards, you might want to eat somewhere else.)
One person, working in a foodservice establishment, can infect multiple people if he or she doesn’t follow safe food handling practices, especially proper handwashing. Proper handwashing is one of the most important precautions in preventing bacteria from spreading from hands to foods. Everyone plays a role in keeping our food safe from harmful bacteria, including farmers, ranchers, distributors, manufacturers, foodservice managers, employees, and customers.
Check out CDC’s Food Safety Website to see what foodborne pathogens have been involved in any recent foodborne illness outbreaks.
In the Dr. X and the Quest for Food Safety video, you learned about PulseNet, a national network of local laboratories that performs DNA “fingerprinting” to better detect a foodborne outbreak in multiple states. Investigate the PulseNet website and prepare a report, including the following:
- What is PulseNet?
- How does DNA “fingerprinting” by PFGE work?
- How has DNA “fingerprinting” been used to prevent foodborne illness?
- Is PulseNet currently tracking your foodborne pathogen?
- How do you think PulseNet will change in the next 10 years? 20 years? 30 years?
Write your own outbreak case and solution. Then, act out the case and have the class investigate and solve it.
The Science and Our Food Supply Curriculum was brought to you by the Food and Drug Administration Center for Food Safety and Applied Nutrition and the National Science Teachers Association.
- FDA Education Team Leader Food Safety Initiative: Marjorie L. Davidson
- FDA Science and Our Food Supply Project Director: Louise H. Dickerson
- FDA/NSTA Associate Executive Director and Science and Our Food Supply Program Director: Christina Gorski
- FDA/NSTA Science and Our Food Supply Program Assistant: Jill Heywood