Chapter 20: Epidemiology - PowerPoint PPT Presentation

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Chapter 20: Epidemiology. Important Point:. If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!. Common Terms. Common Terms. Fraction that get sick!.

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Chapter 20: Epidemiology

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Chapter 20 epidemiology l.jpg

Chapter 20:Epidemiology

Important point l.jpg

Important Point:

If you are having trouble

understanding lecture material:

Try reading your text

before attending lectures.

And take the time to read it well!

Common terms l.jpg

Common Terms

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Common Terms

Fraction that get sick!

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Humans are the most important reservoir of human infectious disease.

Pathogen Reservoirs

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Pathogen Transmission

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Portals of Entry

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Portals of Exit

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The Broad Street Pump.


Common-Source Outbreak

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The Broad Street Pump.

Common-Source Outbreak

Individual cases of (deaths from) cholera.

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Common-Source Outbreak

Sewage contamination of drinking water.

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Propagating Epidemic

Epidemic spreads via multiple sources.

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Index case.

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Zoonoses are Human Diseases with Animal Reservoirs.


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Modes of Transmission

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Contact Transmission


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Direct-Contact Transmission

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Direct Fecal-Oral Transmission

Giardiasis in daycare centers.

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Indirect-Contact Transmission

Methicillin-resistant Staphylococcus aurius (MRSA)?

Beddings are an example of a Fomite, an inanimate object that can transmit pathogens between people.

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Indirect-Contact Transmission

Influenza virus?

Door knobs are another good example of a fomite.

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Droplet Transmission

Less than

one meter


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Airborne Transmission

More than

one meter

Mycobacterium tuberculosis?

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Airborne Transmission

Contact with air from small room containing 12 people.

Contact with air from clean, empty room.

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Waterborne Transmission

Cryptosporidium parvum?

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Waterborne Transmission

Giardiasis from water.

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Foodborne Transmission

Hepatitis A

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Foodborne Transmission

Balantidium coli

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Modes of Transmission

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Portals of Entry

“Many organisms that cause one disease if they enter one body site are harmless if they enter another, e.g., various enteric urinary-tract pathogens.

Epidemiology l.jpg pretty crappy at dealing with cause and effect when associations are subtle.


Do power lines really cause cancer?

What about cell phones?

Epidemiology33 l.jpg pretty crappy at dealing with cause and effect when associations are subtle. However...


What about smoking, a crappy diet, and couch-potato tendencies?

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Types of Epidemiological Studies

A.k.a. analytical

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  • Descriptive studies are simply those that describe the events and rates of disease. They tend to be the first sets of studies done.Quoted or paraphrased from

  • Observational/Analytical studies then look towards finding out the causes of the observed rates. They are called "observational" since the epidemiologist does not intervene in the assignment of exposure.

  • Experimental studies are formal research experiments. The classic example is the randomized control trial where one group is randomly assigned a treatment and a control group gets the placebo or "usual" treatment.

  • Experimental studies are expensive and test a very specific question. Usually a great deal of descriptive and observational studies are done first.

Types of Epidemiologcal Studies

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Just worry about top three and not about percentages.

Relative Nosocomial Frequencies

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Nosocomial Infections

2 million acquire and 20,000 die, per-year in the U.S., from nosocomial Infections.

Nosocomial Infections are, by definition, hospital or clinically acquired.

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Nosocomial Infections

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Compromised Hosts

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Compromised Hosts

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Compromised Hosts

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Compromised Hosts

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Compromised Hosts

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Nosocomial Infections

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Exogenous Infections

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Exogenous Infections

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Endogenous Infections

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Antibiotic Resistance

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Nosocomial Infections

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Chain of Transmission

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Universal Precautions

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Universal Precautions

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Universal Precautions

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Preventing Nosocomial Infections

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Preventing Nosocomial Infections

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