OUTBREAK!
Instructor
- Give each student 1 empty microfuge tube, 1 plastic transfer pipet, 1 index card or small piece of paper, and one marker.
- Each student also receives 1 microfuge tube containing their “bodily fluid.” All students receive a tube containing approximately 0.5ml of water, except the index case person. This person received 1 microfuge tube containing approximately 0.5ml of 0.1N NaOH. Remember who the index case person is, and don’t reveal this to the index case or the other students.
Students
- Each student should write their name at the top of the index card, then write the following:
STUDENT NAME
Partner #1:
Partner #2:
Partner #3:
If you are conducting this activity with less than 15 students – ONLY have the students list Partner #1 and 2 – you will only be able to do 2 exchanges of bodily fluids.
- Each student should remove 2 drops of fluid from their “bodily fluid” tube and place it in their empty tube. Both tubes should be capped and they should write their initials on the top of the tubes with the marker. They should place the tube containing the 2 drops (reference sample) on the bench and not use it until the end of the experiment.
- The other tube is the “sharing” tube. Have students select a partner for sharing. You MUST have an even number of students to do this activity – if you do not, then you should participate as well. Each student should ask another if they would like to “exchange bodily fluids!” At this point, both students should open their sharing tubes. One student should remove all of their own fluid with the pipet from their tube and add it to their partner’s tube. They should carefully pipet up and down several times, then remove approximately half of the fluid and return it to their own tube. At this point, both of the students should return to their own desk and write this person’s name down under “Partner #1,” then they should STOP and not continue with exercise until you tell them to. It is important that every one participating complete one exchange before anyone moves on to his or her next exchange.
- Once all students have completed their first exchange, you may instruct them to move on to their second exchange. This time they should select an individual from the opposite side of the room. They should follow the same procedure outlined above in #3, then return to their own desk and record this person’s name under “Partner #2.” If you are completing this activity with less than 15 students, then skip to Step #6.
- Once all students have completed their second exchange, you may instruct them to move on to their third exchange. This time they should select an individual from a different part of the room. They should follow the same procedure outlined above in #3, then return to their own desk and record this person’s name under “Partner #3.”
- At this point the instructor and/or lab assistant should come around the room to develop the tubes by adding one drop of phenolphthaline (5mg/ml in 95% ethanol). Any tube that is positive (infected or containing any basic solution) will turn bright pink. Negative tubes will remain clear.
- Students should now create a chart of exchanges and their results on the board. From this chart they should begin the steps to determine the index case. They can eliminate all who ended up negative – and anyone who exchanged with a negative individual. They should be able to narrow the individuals down to two – the first exchange, but they cannot determine the index case.
- Discuss with the students how, as good scientists, they would determine the index case with the information that they have available. They will quickly come to the conclusion that they have already saved the appropriate control – their reference sample that is sitting on their desk! You can then add phenylthalein to the 2 suspect individuals and determine the index case.
Reagents and Equipment Needed
- Transfer pipet (1/student)
- Marker (1/table)
- Empty microfuge tube (1/student)
- 0.5 ml aliquots of water (1/student)
- ONE student receives a 0.5ml aliquot of 0.1N NaOH (Index Case)
- Index card (1/student)
- Phenylthalein sol’n (5 mg/ml in 95% ethanol) and transfer pipet to “develop” each student’s reaction
Teacher Tips
- Choose a student as the index case who will not be uncomfortable being the center of attention.
- Be sure that small groups of students do not only exchange with each other – this will make the results difficult to interpret.
Questions For Students
- MATH concepts can actually be introduced here! After the first exchange how many students are positive? After the second? After the third? Did we get the “right” number infected? How could we explain an error? This phenomenon can be used to illustrate the rapid spread of an infectious disease.
- The discussion is likely to turn toward sexually transmitted diseases and this is a good opportunity to discuss the rapid spread of any infectious disease.
- This could also be a place to introduce the concepts of vaccination and the process of flu vaccine development.
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