Epidemiology Chapter 20

1
EpidemiologyChapter 20

• Biology 261
• Microbiology
• Medgar Evers College, CUNY

2
Epidemiology

• The study of the spread, control, and prevention
  of disease in a population.
• An epidemiologist collects and compiles data to
  describe disease outbreaks and come up with
  strategies to prevent future outbreaks and
  protect the population.

3
terminology

• contagious disease- a disease that can be
  transmitted from one host to another.
• A chain of events must occur in order to
  spread the disease.
• A- the pathogen must have a suitable place to
  live. This natural habitat is called the
  reservoir of infection.

4

• The reservoir can be an animal, or an environment
  such as water or soil.
• B- A pathogen must leave the reservoir through a
  body orifice or be shed from any surface. We call
  this the portal of exit.
• C- the pathogen must be transmitted to the next
  host through direct contact or via contaminated
  food, water or air.

5

• D- The portal of entry is the orifice or surface
  that the pathogen enters the next host.

6
Rate factors

• Rate of disease- the proportion of a population
  infected.
• Attack rate- the number of cases developing in a
  group who were exposed to the agent.
• Example If 200 people attended a picnic and 20
  came down with food poisoning, then the attack
  rate is 10.

7

• Morbidity rate- the number of cases of an illness
  in a given time period divided by the population
  at risk.
• Mortality rate- the percentage of population that
  dies from a disease.
• Incidence- the number of new cases in a specific
  time period in a given population at risk.

8

• Prevalence- the number of total existing cases
  both old and new in a population at risk.
• Endemic disease- a disease that is constantly
  present in a population such as the cold and flu.

9

• Epidemic- an unusually large number of cases in a
  population
• Pandemic- the epidemic spreads worldwide.
• Outbreak- a cluster of cases occurring during a
  brief period of time and affecting a specific
  population.

10

• III. The most important steps in preventing
  health care associated infections are to first
  recognize their occurrence and then establish
  policies to prevent both their development and
  spread.
• See perspective 20.1 and know the safety
  procedures that should be followed in a hospital
  setting.