►MEDICAL EPIDEMIOLOGY
MED 6301
University of Minnesota Duluth School of Medicine
Dr. John Kowalczyk
Spring 2010
►Epidemiology- the definition
►Derived from the word ‘epidemic’
►Greek words meaning:
‘Epi’ upon
‘Demos’ people
‘logy’ the study of…
The study of something that comes upon people, usually
that of disease or illness…
►Concerned with distribution and determinants of health and
disease, morbidity and mortality, injuries and disabilities in
human populations
►Determinants refer to factors or events that are capable of
bringing about a change in health
§Biological agents
§Chemical agents
§Physical agents
Classical vs. Clinical Epidemiology
►CLASSICAL: population-oriented
►Community origins of health problems
►Discovering risk factors that might be altered in population
to prevent or delay disease or death
►CLINICAL: use research designs and stats to study patients
in health care settings in order to improve diagnosis and
treatment of diseases
►Improve clinical decisions
Infectious vs. Chronic Epidemiology
►INFECTIOUS: acute, infectious, communicable diseases
►Rely heavily on laboratory and microbiological supports for
confirmation
►CHRONIC: complex sampling and statistical methods to
looking at longevity of chronic illnesses, their cause and
prognosis
Etiology & Natural History of Disease
►If medical or public health does not intervene, disease can
cause havoc
►Public health & medical use stages, mechanisms, & causes
when and how to intervene
►Preventive (P.H.) or therapeutic (medical) is to alter natural
history of disease
Stages, Mechanisms & Causes of Diseases
►Stages of Disease:
§Predisease stage- before pathology begins; any
primary prevention efforts
§Latent stage- disease process begun but
asymptomatic; secondary prevention such as
screenings or drugs to prevent more serious outcomes
§Symptomatic stage- disease manifestations; tertiary
prevention to slow or arrest progression of disease
Mechanisms & Causes of Disease
►Go back far as possible to look for societal causes of disease
►Can be used for methods of prevention
►Biological mechanisms of the human body or of insect
adaptations
►Social and environmental causes can also exacerbate
disease, such as climate changes, etc.
Epidemiology
►Distribution- the frequency and patterns of disease and
health events within groups or populations. Descriptive
epidemiology is used to accomplish this
►Descriptive epidemiology: amount of disease within a
population by:
§Person- age, sex, race, occupation,
§Place- natural barriers, urban/rural
§Time- seasonal, cyclical, short/long term
►Also attempts to search for causes or factors that are
associated with increased risk or probability of disease- here
they are asking “how” and “why” is this disease occurringthis is called Analytical Epidemiology
►Epidemiology deals with populations and NOT with
individual people
Morbidity & Mortality
►Morbidity- refers to illness or disease- sickness
►Mortality- refers to death; looks at causes of death and
ratios of death per so many thousand people
►Epidemic- occurrence of disease in clear excess of normal
expectancy
►Endemic- the usual level of a disease in a population or
region
►Pandemic- epidemics that affect several countries or
continents
Foundations of Epidemiology
►Interdisciplinary Approach
§Biostatistics
§Social & behavioral sciences
§Toxicology/pathology/virology/microbiology
§Clinical medicine
►Methods & Procedures
§Quantification of data is essential!
§Counting number of cases and their distribution to
demographic variables
Historical Background of Epidemiology
► Had its real beginnings with studies of great epidemic
diseases of all times
► Miasma Theory- belief that ‘bad odors’ caused disease!
Moral and religious sin caused disease!
► Contagion theory- ancient Roman physicians theorized that
some human diseases were caused by ‘pathogens’ that
reproduced inside the human body
► Bubonic plague (Black Death)- infectious disease of
inflamed and swollen lymph nodes; came from infested rats
and fleas
► Cholera- intestinal diarrhea from contaminated water; high
fatality rate
► Smallpox- viral disease; very contagious- similar to
chickenpox but more deadly
► Later, chronic diseases, accidents, etc were studied via
epidemiological principals
►Smallpox- completely eradicated from the world in Dec.
1979
Bubonic Plague- Black Death
►60% fatality rate
►20-40 million died in Europe in 5 year period!
►Bacteria not discovered until 1894!
►Bubos- lymph nodes- red spots that turn black
► Raw human sewage dumped into the Thames River or
cesspools, or just dumped out of windows onto streets
below- causing pollution or water supplies
► Snow’s Epidemiological Investigation
Cholera
►Severe intestinal diarrhea from drinking contaminated water
►½ people die from bacterial disease
Hippocrates (400 BC)
► First to make correlations between environmental, dietary,
behavioral conditions
►Wrote “On Airs, Waters, and Places”- discussed his theories
that disease might be associated with the physical environment
and not by superstition or the supernatural
Girolamo Fracastoro (1546)
►The first to develop a coherent germ theory- that living
organisms through direct or airborne contact were responsible
for infecting people with illness (microbial theory of
contagion)
►He recognized 3 modes of disease transmission- person to
person; air; personal objects – like common comb or drinking
cup
►Though accurate in his theory, it was not accepted for
another couple hundred years later!
Edward Jenner (1749- 1823)
►Experimented with inoculating people with cowpox
virus
►Cowpox vaccine was then used to immunize against
smallpox
►Discovered first technique of vaccination
►Demonstrated that person injected with fluid from
coxpox lesion was cross-protected against smallpox
Dr. John Snow (1813- 1858)
►One of most famous epidemiologist of all time
►Was a British medical doctor surgeon (obstetrics and
anesthesiology)
►Huge cholera outbreak in summer of 1854 in Soho, a
London suburb
►Was convinced that disease was spread by contaminated
water- observed a mother washing her baby’s poopy
diapers at the town square pump (baby had just died of
cholera!)
Cholera
►Intestinal diarrhea disease that causes death within
hours after first symptoms of vomitting or diarrhea!
►Old theory of “Miasma” prevailed in that period of timebreathing dirty air from the atmosphere
►In 20 year period, tens of thousands people died in
England
► London Cholera Outbreak
►People did not have running water and no septic
systems
►Communal pumps for drinking water, cooking and
washing
►First suspected contamination of water at Broad Street
pump- 500 people in that neighborhood had died within
10 day period
►Made a geographical map to chart deaths of outbreakwho lived in proximity of pump and who had taken their
water from that pump
►Also tracked down people who did NOT have cholera
and where did they get their water from
►Convinced town officials to remove pump handle so
people couldn’t drink water- outbreak ended!!!
Three Epidemiological Models
1.Epidemiologic Triangle
►model for many years
►Three segments
§Host- degrees that person is able to adapt to
stressors
§Agent- bio, chem., physical
§Environment- influences probability of contact
between host and agent
►Implies that each segment must be analyzed and
understood in order to predict a disease
-if you remove anyone of them you get rid of the problem
(host on meds kills the agent, or elim the environment
such as don’t go to class if you are sick)
agent – bugs, environ = living area (crowded, poor sanitation,
etc)
2.Web of Causation
► Effect never depends on single isolated causes
►develop as a result of chains of causation
►each link is the result of a complex geneaolgy
Example: pregnancy outcomes: if low income, homeless,
unplanned, drug use, poor diet  poorer outcome. As MD
pt education is key!
3.The Wheel Model
►Consists of Hub (host/human) which has genetic make
up as its core
►Surrounding host is the environment
►Biological
►Social
►Physical
►Implies a need to identify multiple etiological factors of
disease without emphasizing the agent of disease
Models: triangle, web, wheels, BEINGS!
►The “B.E.I.N.G.S.” Model (textbook)
►Many risk factors are responsible for why people do or
do not become sick
►“B” biological & behavioral Factors
►Biological factors: (limited control over)
§ age, weight, gender
►Behavioral factors: (controllable)
§ sex practices, smoking, drugs/alcohol
►“E” Environmental Factors
►Air or water pollution
►Effects of poor or good sanitation
►Occupational exposures
►Repetitive strain injuries
►Outdoor exposures to vectors
►“I”.mmunologic Factors
►Vaccinations
►Herd immunity- vaccine protects vaccinated
person from infection in addition to not spreading
disease to others
►Passive immunity from mother to child
►Immunodeficiency disorders
►“N”.utritional Factors
►Importance of diet or lack of healthy diet
►High fat, sodium, cholesterol, etc related to CVD
and other chronic illnesses
►Problems with overweight and obesity issues
►Poverty and starvation; limited nutrients cause
health deficiencies; scurvy; ricketts, etc
►“G”.enetic Factors
►Most difficult factor to change
►Genetic inheritance to protect against disease, or to
promote illness in the person or family
►Distribution of normal and abnormal genes in the
population
►Genetic mutations that lead to diseases,
particularly cancers
►Genetic drifts or shifts in viral changes in disease
outbreaks
►“S”.ervices, Social, & Spiritual Factors
►Medical (or lack thereof) care services
►Social support systems of patients and providers
►Spiritual meaning and purpose of life in relation to
healing and therapy
►Religious practices to self-healing and healthier
lifestyles (Mormons & 7th Day Adventists)
Quick Quiz Assessment – from textbook!! Similar to final
exam questions!
1.Epidemiology is defined as study of factors that influence
health of populations. Application of epidemiologic findings
in populations to decisions in the care of individual patients is:
A.Chronic disease epidemiology
B.Infectious disease epidemiology
C.Clinical epidemiology
D. Descriptive epidemiology
2.For an infectious disease to occur, there must be interaction
between:
A.Behavioral & genetic factors
B.Agent and vector
C.Host and agent
D.Vector and environment
E.Vector and host
Answers:
1. C
2. C