Questions of spread of diseases

  1. Last week, I had a lab for microbiology. The teacher has given a experiement to us. It is a simple experiment which demonstrates the spread. It should be possible from the results to identify the student who introduced the "infection" into the group. This person in known as the "index" case.

    Here is the procedures:
    • Assign yourself a number (1-12), write the no. on a label and stick the label onto your lab coat.
    • Assign yourself a nutrient agar plate. Label with your group no. and your individual no. Make sure you label the underside of your plate not the cover.
    • Wash hands with soap and water and dry your hands.
    • Pick up a sweet and unwrap it.
    • Wash hands again with soap and water. Dry right hand. Leave left hand damp.
    • Take up the sweet with the left hand and handle it in your palm. (You should become quite sticky!)
    • Shake hands (left hands) with a colleague according to the table (1st shake). When shaking hands, really grip the hand well.
    • Using right hand, moisten a swab with sterile water (if your group has a helper they may help with this).
    • Swab your left hand, lift lid of Petri dish and smear swab onto 1/3 of the agar.
    • Discard swab into a lysol jar.
    • Shake hands a second time (2nd shake) with a different person (see table below).
    • Repeat steps 6-8.
    • Shake hands a third time with a third person (3rd shake - see table below).


      Repeat steps 6-8.
    • Wash hands thoroughly after the experiment.
    • Note down the person whom you shook hands with.
    • Incubate all plates at 37C overnight.
    Table: Guide for handshaking experiment

    1st shake 2nd shake 3rd shake

    1 x 2 1 x 4 1 x 6
    3 x 4 2 x 3 3 x 8
    5 x 6 5 x 8 5 x 10
    7 x 8 6 x 7 7 x 12
    9 x 10 9 x 12 9 x 4
    11 x 12 11 x 10 11 x 2


    1. Examine plates and note for growth of orange pigmented colonies. Record results of plates 1-12 in a table (+ light growth, ++ heavier growth, +++ very heavy growth).
    2. From hand-shaking evidence, try to follow course of infection. Who was the source/index case of the epidemic?


    Today, I get a result that No.5 student is the source as No.6 , 8, 10 samples are 3+ infected.. However, there are something I want to ask.


    1) can you give three examples of diseases that may also be spread by this route of transmission.

    2)Name three ways in which you think the spread of these diseases may be controlled.

    3)Sometimes individuals that come into contact with infected individuals do not pick up the disease. Can you explain how this may happen?


    Thanks for help!!!
    Last edit by yatyu on Oct 21, '06
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  2. 3 Comments

  3. by   yatyu
    Do you understand the experiment??

    Questions are:
    1) can you give three examples of diseases that may also be spread by contact transmission.
    2)Name three ways in which you think the spread of these diseases may be controlled.

    3)Sometimes individuals that come into contact with infected individuals do not pick up the disease. Can you explain how this may happen?

    I am very weak in Mic.bio........Please help~thanks!
  4. by   yatyu
    help~help~help~help~~~
  5. by   Daytonite
    you want to look for information on diseases people get by contact. you might try looking for "contact diseases" or "infectious diseases" for more information.

    limiting contact and good hygienic practices with the handling of food and our own body secretions controls diseases. in our country we have public health departments whose function is to keep track of certain specific diseases that must be reported to them and teach those who got the diseases how to prevent them from happening again.

    you also need to read about the concept of immunity for the answer to your third question.

    something that should have been brought out by this exercise was that a person's hands, no matter how many times they are washed, are never free of bacteria. to have a completely sterile touch, a healthcare person must be wearing sterile, uncontaminated gloves.

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