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Epidemiology - Introduction

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Epidemiology - Introduction Study of patterns, distribution of disease (or other events) Cause/transmission Develop strategies for prevention Epidemiologists ... – PowerPoint PPT presentation

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Title: Epidemiology - Introduction


1
Epidemiology - Introduction
Study of patterns, distribution of disease (or
other events)
  • Cause/transmission
  • Develop strategies for prevention

Epidemiologists, health detectives
Dr. Ignaz Semmelweis, Vienna (19th century),
Puerperal fever
2
Epidemiology
  • Principles of Epidemiology
  • Epidemiological studies
  • Infectious Disease Surveillance
  • Trends in Disease
  • Nosocomial Infections

3
Principles of Epidemiology
  • Rate of Disease in a population
  • Reservoirs of Infection
  • Transmission
  • Influential Factors

4
Rates of Disease in a Population
Endemic - disease constantly present in a
particular geographic area
Epidemic - disease with an unusually high
occurrence
Pandemic - worldwide severe epidemic
Morbidity - illness (morbidity rate)
Rate vs. Absolute number
Mortality - death (mortality rate)
5
Outbreak cluster of cases occurring during a
brief time interval and affecting a specific
population.
6
Spread/prevention of disease
Natural habitat
Reservoir
7
Reservoirs of infectious agents
  • Human reservoirs

Symptomatic
ex. cold virus
Asymptomatic carriers
ex. Neis. gon.,
Staph. aureus
humans only reservoir - easiest to control
  • Non-human animal reservoirs

poultry - Salmonella, Campylobacter
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9
Reservoirs of infectious agents
  • Human reservoirs

Symptomatic
ex. cold virus
Asymptomatic carriers
ex. Neis. gon,
Staph. aureus
humans only reservoir - easiest to control
  • Non-human animal reservoirs

poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
10
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11
Reservoirs of infectious agents
  • Human reservoirs

Symptomatic
ex. cold virus
Asymptomatic carriers
ex. Neis. gon,
Staph. aureus
humans only reservoir - easiest to control
  • Non-human animal reservoirs

poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
animal reservoir - difficult to control
12
Reservoirs of infectious agents
  • Human reservoirs

Symptomatic
ex. cold virus
Asymptomatic carriers
ex. Neis. gon,
Staph. aureus
humans only reservoir - easiest to control
  • Non-human animal reservoirs

poultry - Salmonella, Campylobacter
rodents - Yersinia pestis
bats and racoons - rabies virus
animal reservoir - difficult to control
- diseases of animals transmitted to humans
Zoonoses/zoonotic diseases
  • Environmental reservoirs

soil - Clostridium species
13
Transmission
Horizontal (person to person)
Vertical (mother to fetus)
  • contact

direct contact
indirect contact
fomite
  • inanimate object, such as clothing, doorknob
    and so on

Importance of hand washing
droplet
Large microbe-laden respiratory droplets
generally fall to the ground on farther than 3
feet. Importance of covering mouth when cough or
sneeze
14
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15
Transmission
horizontal
Transmission
Natural habitat
vertical
Reservoir
  • contact

direct contact
indirect contact
fomite
- inanimate object
droplet
  • food and water
  • air

very difficult to control
  • vectors

arthropods
flea - Yersinia pestis
mosquito - Plasmodium species (malaria)
16
Black Death (Plague) - Yersinia pestis
Killed 1/4 of the population of Europe between
1346 - 1350 75 of the population in some cities.
Bubonic plague
  • Flea transmits Y. pestis to a human
  • Bacterium is carried to a lymph node.
  • Bubo develops within days
  • Y. pestis begins interfering with the
    inflammatory response - arms itself
  • Multiplying bacteria spill into bloodstream
    (septicemic plague) endotoxin ? shock, DIC
  • 50 - 75 mortality (if untreated)

17
Influential Factors
  • Dose
  • There are few if any infections for which
    immunity
  • is absolute.
  • Incubation Period
  • Population Characteristics
  • Immunity, General Health, Age, Gender,
  • Genetic Background

18
Epidemiological studies
  • Descriptive studies

Risk factors
Person Place
Time
  • Analytical studies
  • Experimental Studies

Which risk factors were/are most relevant?
19
Epidemiological studies
  • Descriptive studies

Person Place Time
Person
20
Epidemiological studies
  • Descriptive studies

Person Place
Time
21
Epidemiological studies
1 2
  • Descriptive studies

Person Place
Time
  1. Rapid rise of sick people
  2. Gradual rise

22
Experimental studies
Experimental studies are done mostly to assess
the value of a particular intervention or
treatment, such as antimicrobial drug therapy.
  • Placebo
  • Double-blind

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24
Rates of Disease in a Population
25
Rates of Disease in a Population
26
Infectious Disease Surveillance
CDC - National Centers for Disease Control and
Prevention
MMWR - Morbidity and Mortality Weekly Report
WHO - World Health Organization Weekly
Epidemiological Record
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30
Trends in Disease
  • Reduction Eradication of Disease
  • Emerging Diseases

31
Trends in Disease
  • Reduction Eradication of Disease
  • - Improved sanitation
  • - Reservior vector control
  • - Vaccination
  • - Antibiotic treatment
  • (Smallpox, eradicated globally)

32
Trends in Disease
  • Emerging Disease
  • - Microbial Evolution, drug-resistance strain
  • - Population expansion
  • - Mass distribution importation of food
  • - Climate change

33
Nosocomial Infections (hospital-acquired
infections) 5-6 patients, 4.5 billion cost
  • Enterococcus species. Part of the normal
    intestinal flora

  • urinary, wound blood infections
  • Escherichia coli. Part of the normal
    intestinal flora
  • Most common cause nosocomial urinary
    infection
  • Pseudomonas species. Grow in moist environment
  • Staphylococcus species. Normal skin flora
  • Common cause of nosocomial pneumonia and
    surgical site infection

34
Epidemiology
  • Principles of Epidemiology
  • Epidemiological studies
  • Infectious Disease Surveillance
  • Trends in Disease
  • Nosocomial Infections

35
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