EXERCISE 7

AN EPIDEMIC CREATED

I. INTRODUCTION

In today's laboratory session we will create an epidemic to show the ease with which microorganisms can be spread by contact, an ever present problem in the clinical area. By the end of this exercise, you should be able to track down the original source of the "infection" using deductive reasoning, an approach similar to that used by public health officials.

From an epidemiological standpoint, two broad etiological principles concerning the spread of infections must be considered: EXPOSURE and SUSCEPTIBILITY. Exposure involves more than contact between the patient and instruments, water, laundry, and waste disposal, etc. The patient's involvement in a variety of diagnostic procedures, requiring movement to other areas of the clinic, further enhances contact with hygienists, technicians, assistants, dentists, and dental students.

Exposure to infection is also increased by the trend toward more complicated dental and surgical diagnostic and therapeutic procedures, such as venipuncture, biopsies, aspirations, extractions, and surgery. Also associated are the use of broad-spectrum antibiotics, corticosteroids, irradiation, and the challenge of the foreign body (sutures and prostheses).

Increased host susceptibility also plays a major role in the promotion of infections, and affected patients comprise three large groups:

• those with impaired cellular or humoral defense mechanisms against infection;
• those in whom the physical barriers against invasion by pathogens are compromised; and
• those receiving therapy that induces defects in normal host defense mechanisms.

Often it is not possible to keep problems that arise in the clinic from spreading to the community. Clinic patients may take home transmissible infections without being apparently ill. Members of the clinic staff may become asymptomatic carriers of microorganisms and infect their patients, families and other people in their communities. (The wearing of surgical gloves by dental professionals protects these clinicians from infection, but puts others at risk from spread of infection, if the gloves are worn outside the work station or cubicle.)

II. LAB WORK

• 1 pair of disposable gloves
• 1-2 tubes containing sterile, moist, cotton swabs
• 1-2 Nutrient Agar plates (NA)
• 1 petri dish, numbered, containing candy that has been inoculated with either Serratia marcescens or Staphylococcus epidermidis
• Table of hand-shaking sequence

Procedure:

The class will be divided into several groups of students for this experiment. The lab instructor will identify these groups. Each of the groups should have the same results.

One student in each group will unknowingly act as the epidemic initiator. His/her candy is contaminated with Serratia marcescens. The process of shaking hands will simulate the contact that is necessary for an epidemic to spread. In addition, we will assume that all of the "population" is at risk.

At the next lab session, the results will be tabulated and you will be responsible for discovering the initiator of this epidemic.

1. Before you begin, stick the numbered label on your lapel, and label your NA plate(s) with your name and candy number. Even-numbered students, (2, 4, 6, etc.) have 2 NA plates that should be labeled ROUND 1 and ROUND 2. Odd-numbered students have only 1 NA plate that should be labeled ROUND 2.
2. Put on your pair of disposable gloves.
3. On a signal from the lab instructor, rub the candy from your petri dish between the palms of your gloved hands. Return the candy to the petri dish for disposal later.
4. Student #1 from each group will start by shaking hands with another member of his/her group Follow the table handed out in lab, and the directions from the lab instructor. Shake hands only in your group.
5. Then, student #2 will shake hands with the student indicated in the table, and so it will progress, following the order given in the table, until each person has shaken hands with at least one other person.
6. Even-numbered students will then swab their right palms with a moist sterile cotton swab, and smear the swab on the ROUND 1 agar plate. Swab the entire plate, turning the swab so that all sampled bacteria are transferred to the plate. Replace the used swab in the testtube from which it came, for disposal later.
7. After the first round of swabbing is complete, the second round of handshaking begins. Again, following the table listing for Round 2, student #1 from each group will start by shaking hands with another member of his/her group.
8. When the second round of handshaking is completed, ALL students swab their right palms with a sterile swab and inoculate their plates by swabbing the entire plate, turning the swab so that all sampled bacteria are transferred to the plate. Replace the used swab in the testtube from which it came, for disposal later.
9. Place the NA plates in the correct plate carrier, as specified by the lab instructor.
10. Collect all used materials and dispose of them in the correct containers.

ONLY THEN, REMOVE THE GLOVES AND DISPOSE OF THEM IN THE LARGE BIOHAZARD BAG. WASH YOUR HANDS WELL.

YOU CANNOT DEPEND UPON DISPOSABLE GLOVES TO KEEP YOUR HANDS FROM BEING CONTAMINATED.