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Epidemiology - Introduction. Study of patterns, distribution of disease (or other events). Cause/transmission. Develop strategies for prevention. Epidemiologists, “health detectives”. Dr. Ignaz Semmelweis, Vienna (19 th century), Puerperal fever. Epidemiology. Principles of Epidemiology

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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, “health detectives”

Dr. Ignaz Semmelweis, Vienna (19th century), Puerperal fever


Epidemiology

  • Principles of Epidemiology

  • Epidemiological studies

  • Infectious Disease Surveillance

  • Trends in Disease

  • Nosocomial Infections


Principles of Epidemiology

  • Rate of Disease in a population

  • Reservoirs of Infection

  • Transmission

  • Influential Factors


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)


Outbreak– cluster of cases occurring during a brief time interval and affecting a specific population.


Transmission

Spread/prevention of disease

Natural habitat

Reservoir


Transmission

Natural habitat

Reservoir

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


Transmission

Natural habitat

Reservoir

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


Transmission

Natural habitat

Reservoir

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**


Transmission

Natural habitat

Reservoir

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


Transmission

Natural habitat

Reservoir

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


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)


flea

flea

rodent

rodent

flea

“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)


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


Epidemiological studies

  • Descriptive studies

Risk factors

Person

Place

Time

  • Analytical studies

  • Experimental Studies

Which risk factors were/are most relevant?


Epidemiological studies

  • Descriptive studies

Person

Place

Time

Person


Epidemiological studies

  • Descriptive studies

Person

Place

Time


Epidemiological studies

1

2

  • Descriptive studies

Person

Place

Time

  • Rapid rise of sick people

  • Gradual rise


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


Endemic

Epidemic

Pandemic

Morbidity

Mortality

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)

Mortality - death (mortality rate)

Rates of Disease in a Population


Infectious Disease Surveillance

CDC - National Centers for Disease Control and Prevention

  • MMWR - Morbidity and Mortality Weekly Report

  • WHO - World Health Organization

    • Weekly Epidemiological Record


Trends in Disease

  • Reduction & Eradication of Disease

  • Emerging Diseases


Trends in Disease

  • Reduction & Eradication of Disease

    - Improved sanitation

    - Reservior & vector control

    - Vaccination

    - Antibiotic treatment

    (Smallpox, eradicated globally)


Trends in Disease

  • Emerging Disease

    - Microbial Evolution, drug-resistance strain

    - Population expansion

    - Mass distribution & importation of food

    - Climate change


Nosocomial Infections(hospital-acquired infections)5-6% patients, $4.5 billion cost

Enterococcus species. Part of the normal intestinalflora

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


Epidemiology

  • Principles of Epidemiology

  • Epidemiological studies

  • Infectious Disease Surveillance

  • Trends in Disease

  • Nosocomial Infections


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