Students exchange clear solutions to represent contact with body fluids. A hidden “infected” sample (sodium hydroxide) reacts with phenolphthalein to produce a pink color, revealing which students have become “infected.” The activity ends with an epidemiology-style investigation to identify the original carrier.

1. Number a set of culture tubes and pipets, one for each student.
2. Randomly select one “carrier” tube and fill it with 5 mL sodium hydroxide solution. Fill the rest with 5 mL deionized water.
3. Give each student a tube, pipet, and index card to record their exchanges.
4. Students make three exchanges of solution with different partners, mixing after each exchange.
5. After three rounds, add 2 drops of phenolphthalein to each tube. A pink color indicates infection; clear or yellow indicates no infection.
6. As a class, record “negative” students on the board. Use the process of elimination and tracing of contacts to identify the original carrier.
7. Conclude with discussion of how diseases spread and how epidemiologists trace infection sources.

The Red Plague - FlinnScientific:

📄 Viral Infection! - Flinn Scientific: https://www.flinnsci.com/api/library/Download/2418b9c3705147c3b508efcf5383c8b8?srsltid=AfmBOoojIm0RAc8wSERLAA8M1NmLIpRI6aQq9uKDTLJ7_oTwegXS4nJ7

📄 Tracking a Virus - ncwit.org: https://www.teachengineering.org/activities/view/duk_virus_mary_act

• Use paper cups instead of test tubes, and 'swap fluids' during a contact by pouring all of the solution into one cup then splitting it in half.
• Vary the number of exchanges or initial carriers to change the infection rate.
• Use two carriers to simulate multiple outbreak sources.
• For smaller classes, reduce exchanges to two; for larger classes, increase to four.
• Compare how quickly infections spread when students only exchange within groups versus freely across the class.

• Sodium hydroxide is corrosive—wear goggles, gloves, and aprons.
• Students should never squirt or splash solutions.
• Clean spills immediately with damp paper towels.
• Wash hands thoroughly after the activity.

• How realistic is this model compared to real viral transmission?
• Could you tell who the original carrier was before the indicator was added?
• How does increasing the number of exchanges affect infection rate?
• What difficulties arise when trying to trace the original source of an outbreak?
• How does this simulation relate to real-life epidemics such as influenza or HIV?
• Why are measures like isolation or limiting contact effective at slowing the spread of disease?