BI 234 Epidemiology Fall After completing this laboratory exercise, the student should have an understanding of and be able to:

Transcription

1 Objectives After completing this laboratory exercise, the student should have an understanding of and be able to: 1. Define, explain and give examples for each of the following: epidemic point source pandemic ubiquity direct transmission carrier vector propagated endemic outbreak reservoir indirect transmission vehicle fomite 2. Determine the origin of a simulated propagated epidemic. 3. Discuss the various factors involved in the spread of disease. 4. Determine the factors that influence the effectiveness of hand washing.

2 Introduction Epidemiology Epidemiology is that field of study which deals with the transmission and occurrence of disease. Though the majority of microbes do not have any negative effects on people (and we know that actually, many have beneficial effects), it is clear that a few bacteria, fungi, and viruses do thrive at our expense. A microbe that causes disease in a population is called a pathogen. The best way for the human population to cope with the existence of such pathogens is to understand the nature of each individual pathogen and the patterns of disease that it causes in its host population. Developing an understanding of disease patterns requires the analysis of such disease factors as the pathogen s origin, its prevalence in society, and its modes of transmission. Direct transmission occurs when a pathogen is transmitted via human contact. STDs, skin bacteria, etc. are examples. Indirect transmission occurs when a pathogen is spread not by direct human contact, but by an intermediate factor. These intermediates have specific names dependent upon the nature of the source. Vehicles are foodborne or waterborne sources of a pathogen. Vectors are arthropod/insect intermediates. Fomites are inanimate objects which may spread disease. How a disease is spread is also an important factor to consider. A point source epidemic is one that is acquired by all affected individuals from a specific source, such as a contaminated well or a common dish at a buffet. A propagated epidemic is one that is transmitted from one or many individuals to other people. In this lab, we will simulate a propagated epidemic spread via direct transmission. Hand Washing As the myriad signs around campus state Hand washing is the most effective means of preventing the spread of disease. Unfortunately, most people do not wash their hands effectively, if at all. Spend a few minutes in the bathrooms on campus and you will be witness to the level of hygiene practiced at BCC, or, rather, the lack of hygienic practices. Proper hand washing requires three fundamental things: soap, as warm as water as you can tolerate, and time. The purpose of this lab exercise will be to determine which of the three factors plays the greatest role in effective handwashing.

3 Materials: (per group) Methods 2 dishes containing a Swedish fish (DO NOT EAT!) 6 TSA plates Cotton swabs Hand washing materials Simulated Epidemic Wearing gloves, each individual will thoroughly contaminate one gloved hand with a potentially contaminated Swedish fish and proceed to simulate an epidemic by shaking hands with their classmates. 1. Label your TSA plates with date, name, section number and Swedish fish number. 2. Wet two cotton swabs with sterile water; place them back their respective packages. 3. Place exam gloves on both hands. 4. Remove the Swedish fish from its Petri dish and massage the Swedish fish on the inside palm and fingers of your right hand to completely cover the surface with the potential pathogen. 5. Remove the glove from your left hand and place it in the biohazard bag. 6. Transmission Follow these directions carefully and precisely Part One 1. Starting with the person sitting in the front left-hand corner of the room, in sequence, each student will use their right hand to shake hands with the person directly to their right at the same bench (from left to right) 2. After the first bench is finished, the last person will shake hands with the person behind them. 3. Starting with this student in the second row, each person, in sequence, will shake hands with the student to their left. 4. After the second bench is finished, the last person will shake hands with the person behind them. 5. This sequence will be repeated until each bench has participated. 6. Swab your right hand with one of the cotton swabs and inoculate a TSA plate.

4 Part Two 1. Starting with last person in the room from Part One, shake hands in the opposite direction. 2. Shake right hands, in sequence, until everyone has shaken hands a second time 3. Swab your right hand with one of the cotton swabs and inoculate the second TSA plate. 4. Turn plates upside down and place it in the 25 C incubator.

5 Hand Washing 1. Label two TSA plates with date, name, and section number. Label one plate before and one plate after. 2. Wet two cotton swabs with sterile water; place the swabs back in their packages. 3. Use a wet swab to swipe and collect bacteria from your hand (left or right). Be sure to sample the same hand during the entire experiment. 4. Inoculate the before TSA plate with the first swab. Be sure to cover the entire area. 5. Wash or sanitize your hands using the appropriate parameters and the materials. 6. Use the second wet swab to swipe and collect bacteria from your now clean hand (same hand as in #3). 7. Inoculate the after TSA plate with the second swab. Be sure to cover the entire area. 8. Your partner should now do their hands as well. 9. Turn plates upside down and place in 35 C incubator. Hand washing parameters used: (circle one) Time Cleanser Water temperature Specific Parameter Tested

6 Results Simulated Epidemic 1. Did your plate have growth? 2. Qualitatively indicate the amount of growth on your plate and others in your lab. Fill out the chart below with a minus (-) sign for no growth and one or more plus (+) signs for varying amounts of bacterial growth (+, growth present; +++, much growth present). First Plate Bench 1 Bench 2 Bench 3 Bench 4 Seat 1 Seat 2 Seat 3 Seat 4 Second Plate Bench 1 Bench 2 Bench 3 Bench 4 Seat 1 Seat 2 Seat 3 Seat 4 3. From this data, who is the most likely source of the pathogen?

7 Hand Washing 1. What parameters did your group test? 2. Fill out the chart below with the results of the class. Person 1 Person 2 Person 3 Person 4 Person 5 Person 6 Person 7 Person 8 Person 9 Person 10 Person 11 Person 12 Person 13 Person 14 Person 15 Person 16 Method/Parameter Growth Before Growth After 3. What parameter(s) seem to be most critical to successful hand washing? 4. What method/cleanser would you recommend to a friend?

8 Questions 1. What is the difference between an endemic disease and an epidemic disease? 2. In our simulated epidemic, was this an example of a point source epidemic or a propagated epidemic? 3. You and your spouse go out to dinner, enjoying different entrees. The next day, your spouse develops abdominal cramps and diarrhea. What is the most likely explanation for these symptoms? What do you need to know to confirm this hypothesis. Is this an example of a fomite, vehicle or vector? 4. What is the difference between direct and indirect transmission of disease? What are some examples of both? 5. How does soap work?