Mission Microbe
Why is collecting evidence from healthy people sometimes just as important as collecting evidence from sick people?
Healthy people provide a comparison that helps investigators identify which exposures are actually linked to illness.
Three patients became sick after eating different meals. Explain why investigators should not assume the meals caused the illnesses.
Additional evidence is needed because correlation alone does not prove causation.
I can grow in refrigerated foods. Explain why this makes me harder to control than many other bacteria. Who am I?
Listeria monocytogenes because refrigeration does not stop its growth.
Explain why washing vegetables after cutting raw chicken on the same cutting board may still not prevent illness.
Cross-contamination may have already transferred harmful bacteria.
Why do investigators continue collecting evidence even after finding bacteria in a food sample?
One positive sample does not prove it caused the illnesses.
A laboratory identifies bacteria in a food sample, but none of the sick patients report eating that food. What should investigators do next?
Continue interviewing patients, verify laboratory results, investigate other possible food sources, and collect additional evidence.
Your interviews reveal that every sick person attended a different restaurant. Develop a strategy to identify a common exposure.
Compare suppliers, ingredients, dates, food histories, and distribution records.
Three microbes cause diarrhea. One is destroyed by antibiotics, one is not because it is a virus, and one produces toxins before you even eat the food. Identify all three.
Salmonella, Norovirus, Clostridium botulinum (or Bacillus cereus, depending on discussion).
Two restaurants prepare identical meals, but only one causes illness. Explain three possible reasons why.
Improper storage, cross-contamination, sick food handler, improper cooking temperatures, contaminated ingredients.
Patient interviews identify strawberries, but laboratory tests identify lettuce. How should investigators resolve this conflict?
Collect more evidence, repeat testing, conduct traceback investigations, and compare all data.
Scientists discovered that two different restaurants served contaminated food. Explain how investigators could determine whether the contamination happened at the restaurants or earlier in the food supply chain.
Compare suppliers, conduct traceback investigations, inspect food handling practices, and analyze laboratory evidence.
Patient interviews and laboratory results point to different foods. Explain how epidemiologists decide what evidence deserves more weight.
Consider the sample size, laboratory confirmation, interview consistency, and additional testing.
Investigators find a microorganism in poultry, eggs, and reptiles. Explain how those clues help identify me. Who am I?
Salmonella
A restaurant passes its health inspection but later causes an outbreak. Explain how both statements can be true.
Contamination may have occurred after inspection or during food handling.
What would be five important questions to help identify the source of a foodborne outbreak?
Foods eaten, where purchased, dates, symptoms, travel, leftovers, other sick family members, etc.
During an outbreak investigation, one laboratory result does not align with the other evidence. Explain why investigators should not immediately ignore or accept that result.
They should verify the result through repeat testing, evaluate possible errors, and compare it with all other available evidence before drawing conclusions.
An outbreak appears in five states over three weeks. Explain how investigators determine whether all illnesses belong to the same outbreak.
Compare bacterial DNA, timing, patient histories, food distribution, and traceback information.
My symptoms resemble those of several other pathogens. Describe what laboratory evidence scientists would need to prove I caused the outbreak. Who am I?
DNA sequencing, cultures, Gram stain, biochemical testing, or PCR.
Design a food safety plan that would reduce the chance of Listeria contamination in a deli kitchen.
Cleaning schedules, refrigeration monitoring, separating ready-to-eat foods, sanitizing equipment, employee training, testing.
Your team must decide whether to issue a public warning before all testing is complete. How would you, as investigators, balance protecting the public with avoiding unnecessary panic?
Evaluate strength of evidence, severity of illness, risk to the public, and uncertainty before making recommendations.
Imagine you are the lead FDA investigator. Create a complete investigation plan that identifies the outbreak source, protects the public, and prevents future outbreaks. Explain why each step is necessary.
interviewing patients, laboratory testing, traceback investigations, environmental sampling, identifying contamination sources, issuing recalls when appropriate, and recommending prevention strategies
Create an investigation plan for an outbreak that involves restaurants, grocery stores, farms, and food processors.
Prioritize interviews, laboratory testing, traceback investigations, environmental sampling, and interagency communication.
A newly discovered microorganism survives freezing temperatures, forms spores, and contaminates vegetables. Design three laboratory tests that would help identify it and explain why each test is useful.
Examples include Gram stain, microscopy, culture characteristics, DNA sequencing, biochemical testing, and spore staining with justification.
A nationwide outbreak begins with one contaminated ingredient. Explain how that ingredient could eventually make thousands of people sick.
Food processing, distribution networks, restaurants, grocery stores, delayed detection, and widespread exposure.
Your investigation has conflicting interviews, incomplete laboratory results, and multiple possible food sources. As investigators, what would be your final recommendation for public health officials?
Prioritize the strongest evidence, identify additional data needed, explain uncertainty, and justify recommendations using scientific reasoning.