Epidemiology
A Brief Introduction
Epidemiology - definition
epi
– means “on, upon, befall”
epidermis: upon the body, skin
demo
– means “people, population, man”
demographics
ology
– means study of
Literally epidemiology: that which befalls
man
Epidemiology - definition
Def: an investigative method used to detect
the cause or source of diseases, disorders,
syndromes, conditions, or perils that cause
pain, injury illness, disability, or death in
human populations or groups
History
Dr. John Snow is famous for his investigations
into the causes of the 19th Century Cholera
epidemics.
He began with a comparison between the
death rates from areas supplied by two
adjacent water companies in Southwark.
His identification of the Broad Street pump as
the cause of the SoHo epidemic is considered
the classic example of epidemiology.
History
He used chlorine in an attempt to clean the
water and had the handle removed, thus
ending the outbreak. (It has been questioned
as to whether the epidemic was already in
decline when Snow took action.)
This has been perceived as a major event in
the history of public health and can be
regarded as the founding event of the science
of epidemiology.
Purposes of Epidemiology
To explain the etiology (cause) of a
single disease or group of diseases
using information management
To determine if data are consistent with
proposed hypothesis
To provide a basis for developing control
measures and prevention procedures for
groups and at risk populations
Terms to know
Virulence the extent of pathogenicity or strength
of different organisms
the ability of the pathogen to grow, thrive, and to
develop all factor into virulence
the capacity and strength of the disease to produce
severe and fatal cases of illness
Invasiveness the ability to get into a susceptible
host and cause a disease within the host
The capacity of a microorganism o enter into and grow
in or upon tissues of a host
Terms to know
endemic: the ongoing, usual level of, or
constant presence of a disease in a given
population
hyperendemic: persistent level of activity
beyond or above the expected prevalence
holoendemic: a disease that is highly
prevalent in a population and is commonly
acquired early in life in most all of the children
of the population
Terms to know
epidemic: outbreak or occurrence of one
specific disease from a single source, in a
group population, community, or geographical
area, in excess of the usual level of
expectancy
pandemic: epidemic that is widespread
across a country, continent, or large populace,
possible worldwide
incidence: the extent that people, within a
population who do not have a disease,
develop the disease during a specific time
period
Terms to know
prevalence: the number of people within a
population who have a certain disease at a
given point in time
prevalence relies on 2 factors:
How many people have had the disease in the past
Duration of the disease in the population
7 Uses of Epidemiology
1. To study the history of the disease
Studies trends of a disease for the prediction of trends
Results of studies are useful in planning for health services and
public health
2. Community diagnosis
What diseases, conditions, injuries, disorders, disabilities, defects
causing illness, health problems, or death in a community or region
3. Look at risks of individuals as they affect populations
What are the risk factors, problems, behaviors that affect groups
Groups are studied by doing risk factor assessments
4. Assessment, evaluation and research
How well do public health and health services meet the problems
and needs of the population
Effectiveness; efficiency; quality; access; availability of services to
treat, control or prevent disease
7 Uses of Epidemiology
5. Completing the clinical picture
Identification and diagnostic process to establish that a
condition exists or that a person has a specific disease
Cause effect relationships are determined, e.g. strep
throat can cause rheumatic fever
6. Identification of syndromes
Help to establish and set criteria to define syndromes,
some examples are: Down, fetal alcohol, sudden
death in infants, etc.
7. Determine the causes and sources of diseases
Findings allow for control prevention, and elimination
of the causes of disease, conditions, injury, disability,
or death
The Epidemiology Triangle
Time
The Epidemiology Triangle
The agent is the cause of the disease
Can be bacteria, virus, parasite, fungus, mold
Chemicals (solvents), Radiation, heat, natural toxins
(snake or spider venom)
The host is an organism, usually human or
animal, that harbors the disease
Pathogen disease-causing microorganism or
related substance
Offers subsistence and lodging for a pathogen
Level of immunity, genetic make-up, state of health,
and overall fitness within the host can determine the
effect of a disease organism can have upon it.
Disease Transmission
Carrier: one that spreads or harbors an infectious
organism
Some carriers may be infected and not be sick. e.g. Typhoid Mary
Mary Mallon (1869
– 1938) was the first person in the United
States to be identified as a healthy carrier of typhoid fever. Over the
course of her career as a cook, she infected 47 people, three of
whom died from the disease.
Her notoriety is in part due to her vehement denial of her own role
in spreading the disease, together with her refusal to cease working
as a cook.
She was forcibly quarantined twice by public health authorities and
died in quarantine. It is possible that she was born with the disease,
as her mother had typhoid fever during her pregnancy.
Levels of Disease
Diseases have a range of seriousness, effect, duration,
severity, and extent
Classified into 3 levels
Acute relatively severe, of short duration and often
treatable
usually the patient either recovers or dies
Subacute intermediate in severity and duration, having
some acute aspects to the disease but of longer duration
and with a degree of severity that detracts from a complete
state of health
Patient expected to eventually heal
Chronic less severe but of long and continuous duration,
lasting over a long time periods, if not a lifetime
Patient may not fully recover and the disease can get worse
overtime
Life not immediately threatened, but may be over long term