Normal classroom safety guidelines should be observed.
Procedure
Explanation (15 minutes)
1. Tell your students they are now going to learn how epidemiologists or “disease
detectives” study an infectious disease. They use a method called The
Epidemiologic Triangle.
2. Hand out the Student Reproducible 2, The Epidemiologic Triangle. Draw a large
triangle on the board.
3. Ask a student to read the definition of “agent” written on his or her handout. This
is the “what” of the Triangle. Ask the class if they know the agent for any of the
diseases they discussed earlier. (Most of them will not.) Tell them that the
information is available to doctors and scientists, and also may be available on
the Internet. They will be doing some research into agents at a later time.
As an example, you might want to talk briefly about an agent they might be
familiar with, E. coli. Some forms of the bacteria E. coli cause food poisoning.
(You may have a news story about an example of people who got sick from
eating food that was infected with E. coli.) E. coli bacteria can be found in the
intestines and waste of animals and people. The bacteria are transmitted through
food, water, or anything else contaminated with feces. When meat containing the
E. coli bacteria is consumed uncooked or undercooked, it can make you sick.
Cold temperatures, for example in the refrigerator, can keep E. coli from
multiplying quickly. Warm temperatures—for example, room temperature or
being out in the sun—make the bacteria multiply quickly. High heat kills the
bacteria. That’s why meat needs to be cooked thoroughly and hot foods need to
be refrigerated immediately after a meal. (For more information on food safety,
visit the BAM! Web site article, Power Packing.
4. Ask a student to read the definition of “host.” This is the “who” of the Triangle.
Under this heading, students can also describe the symptoms of the disease a
“host” may experience. For E. coli, they include nausea, diarrhea, and vomiting.
Among older people or babies whose bodies are not as strong, or people with
another illness, it may cause death.
5. Ask a student to read the definition of “environment.” This is the “where” of the
Triangle. You can again use E. coli as an example. The bacteria are found in the
digestive tract of animals and people, and are spread through their feces. When
livestock is slaughtered, it is possible for meat to become contaminated with E.
coli if it comes in contact with the animal's infected feces. That infected meat
then has the chance to make you sick if it is under- or improperly cooked. E. coli
can be killed by thorough cooking, which is one reason meat should never be
eaten raw or rare. E. coli can live in water and can infect fruit and vegetables
irrigated by that water. Usually water used to irrigate is tested to be sure it does
not contain E. coli or other dangerous bacteria and produce found in the grocery
store is washed before it is packed. (It is still a good idea to wash fruits and