Introduction to EPIDEMIOLOGY

Daniel CothranBIOL 422 – Microbiology

10/19/2009

Overview

• Introduction to Public Health• What is Epidemiology?

History Who Uses It?

• Terminology• Infectious Disease Transmission• The Host Community• Disease Burden

Introduction to Public Health

Introduction to Pubic Health

What is it? A field devoted to the promotion and

maintenance of well-being

Attributes Multidisciplinary Often focused on prevention rather than

treatment (upstream) Operates on multiple levels

Introduction to Public Health (cont’d)

What is Epidemiology?

What is Epidemiology?

Two Definitions:• “The study of the occurrence, distribution,

and determinants of health and disease in a population”

• “The study of the distribution and determinants of disease frequency in human populations and the application of this study to control health problems”

History of Epidemiology• Almost 400 years old!• “First” epidemiologist:

John Graunt• William Farr• Controlled trials! (public

health people love these)• Shift from studying

infectious to chronic diseases

• Divergence: molecular and genetic epidemiology vs. social epidemiology

Who Uses Epidemiology?

• Health Care Service Providers• Governments

Legislature Health Departments

• International Health & Development Agencies• Community-based NGOs• Researchers• Journalists• You

Terminology

Terminology

Terminology (cont’d)

• Case An instance of a disease or health condition in an

individual• Incidence

Number of new cases of a disease or health condition in a population over a given period of time

• Prevalence Number of new and existing cases of a disease or

health condition in a population over a given time period

Hand Check!

What’s are the incidence and prevalence for the class?• Incidence = _____ /

~70 (per hour)

• Prevalence = ___ +___ /~70 (per hour

Symptoms of Glitter Disease

Terminology (cont’d)

• Morbidity Used commonly to mean illness Morbidity Rate: refers to the incidence of disease in a

population• Mortality

Used commonly to mean death Mortality Rate: refers to the incidence of death in a

population➡Morbidity from a disease can be high without

mortality being high

Terminology (cont’d)

• Host – organism capable of supporting the growth of a virus or other parasite

• Carrier – sub-clinically infected individuals who may spread a disease Examples?

Terminology (cont’d)

• Reservoir – source of viable infectious agents from which individuals may be infected Vector – agent (usually insect or animal) able to

carry pathogens from one host to another Vehicle – nonliving source of pathogens that infect

large numbers of individuals (food, water, etc)

Terminology (cont’d)

• Zoonosis – a disease, primarily of animals, that is occasionally transmitted to humans Examples: avian and swine flu

Don’t forget to cover your snout when you sneeze!

Terminology (cont’d)

Disease Progression• Infection• Incubation Period• Acute Period• Decline Period• Convalescent Period

Disease Transmission

Direct Host-to-Host Transmission

• Pathogen transmitted directly from host to host Respiratory illnesses Sexually-transmitted

infections Skin infections

Vampirism?

Indirect Host-to-Host Transmission

• Transmitted through living agents (vectors) or inanimate agents (vehicles)

Mosquito: vector Lenoir food: vehicle

What type of transmission was at work here?

Epidemics

Common-source epidemic• Transmission can occur

rapidly• Classic example: London’s

cholera epidemic in the 1850’s

Epidemics (cont’d)

Host-to-Host Epidemic• Typically occurs over a longer period of time

than the common-source epidemic• Examples: Influenza, Chickenpox

Epidemics (cont’d)

The Host Community

Coevolution

• The continued existence of host and pathogen frequently requires coevolution

• Examples Myxoma Malaria E. coli

Herd Immunity

Is this what it is?

Herd Immunity (cont’d)

• Resistance of a group to infection due to the immunity of a high proportion of individuals

• Depends on: Density of thepopulation Virulence of theagent

The Host Community

• Disease is not purely biological!• Behavior matters

Examples of protective behaviors?

• Who you are matters Racism sexism classism Etc.

Disease Burden

Disease Burden

Disease Burden (cont’d)

Sources• Aschengrau A, Seage G. Essentials of Epidemiology in Public Health. 2nd Ed. Jones and Bartlett

Publishers, Inc. Salsbury, MA, 2008.• Clark DP, Dunlap PV, Madigan MT, Marinko MM. Brock Biology of Microorganisms. 12th Ed. Pearson

Edu, Inc. San Fransisco, CA, 2009.• http://a3.vox.com/6a00c2252582c1f21900d4144dabbb6a47-500pi• http://himetop.wdfiles.com/local--files/broad-street-pump/Broad%20Street%20Pump.jpg• http://mydogumentary.files.wordpress.com/2009/08/mosquito.jpg• http://farm4.static.flickr.com/3123/2604408184_5718abdaa8.jpg• http://www.independent.co.uk/multimedia/archive/00079/twilight_79981t.jpg• http://images.buyfairycostumes.com/deluxe-fairy-makeup.jpg• http://www.measlesinitiative.org/mi/photos• http://www.whspip.co.uk/images/occu2.jpg• http://www.msf.ca/blogs/cholera/files/2009/03/latrine.jpg• http://www.youtube.com/watch?v=6Pq98sZSBtc• http://www.medicine.manchester.ac.uk/images/epidemiology/home_checkerboard.jpg• http://www.youtube.com/watch?v=LU8DDYz68kM• http://www.dailytarheel.com/content/fewer-h1n1-cases-reported