EPIDEMIOLOGYIntroduction

CLASSICALLY SPEAKING

Epi = upon Demos = people Ology = science Epidemiology = the science which deals with

what falls upon people….. Bridge between biomedical, social and

behavioral sciences

EPIDEMIOLOGY - DEFINITION

Some see epidemiology as science, others see it as a method.

Generally seen as a scientific method to investigate disease

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

EPIDEMIOLOGY – WHAT IS IT? The study of the nature, cause,

control, and determinants of the frequency and distribution of disease, disability, and death in human populations.

Also involves characterizing the distribution of heath status, diseases, or other health problems in terms of age, sex, race, geography, religion, education, occupation, behaviors, time, place, person, etc.

This characterization is done in order to explain the distribution of a disease or health related problems in terms of the causal factors

EPIDEMIOLOGY – WHAT IS IT? Serves as the foundation and logic of

interventions made in the interest of public health and preventive medicine.

It is considered a cornerstone methodology of public health research, and is highly regarded in evidence-based medicine for identifying risk factors for disease and determining optimal treatment approaches to clinical practice.

EPIDEMIOLOGY – WHAT IS IT? In the work of communicable and non-

communicable diseases, the work of epidemiologists range from outbreak investigation to study design, data collection and analysis including the development of statistical models to test hypotheses and the documentation of results for submission to peer-reviewed journals.

Epidemiologists may draw on a number of other scientific disciplines such as biology in understanding disease processes and social science disciplines including sociology and philosophy in order to better understand proximate and distal risk factors

HISTORY The Greek physician Hippocrates is

sometimes said to be the father of epidemiology. He is the first person known to have examined the relationships between the occurrence of disease and environmental influences. He coined the terms endemic (for diseases usually found in some places but not in others) and epidemic (for disease that are seen at some times but not others).

One of the earliest theories on the origin of disease was that it was primarily the fault of human luxury. This was expressed by philosophers such as Plato and Rousseau, and social critics like Jonathan Swift

HISTORY In the medieval Islamic world, physicians

discovered the contagious nature of infectious disease. In particular, the Persian physician Avicenna, considered a "father of modern medicine," in The Canon of Medicine (1020s), discovered the contagious nature of tuberculosis and sexually transmitted disease, and the distribution of disease through water and soil.

Avicenna stated that bodily secretion is contaminated by foul foreign earthly bodies before being infected. He introduced the method of quarantine as a means of limiting the spread of contagious disease.

He also used the method of risk factor analysis, and proposed the idea of a syndrome in the diagnosis of specific diseases.

HISTORY When the Black Death (bubonic plague)

reached Al Andalus in the 14th century, Ibn Khatima hypothesized that infectious diseases are caused by small "minute bodies" which enter the human body and cause disease.

Another 14th century Andalusian-Arabian physician, Ibn al-Khatib (1313–1374), wrote a treatise called On the Plague, in which he stated how infectious disease can be transmitted through bodily contact and "through garments, vessels and earrings."

HISTORY In the middle of the 16th century, a famous

Italian doctor from Verona named Girolamo Fracastoro was the first to propose a theory that these very small, unseeable, particles that cause disease were alive.

They were considered to be able to spread by air, multiply by themselves and to be destroyable by fire.

In 1543 he wrote a book De contagione et contagiosis morbis, in which he was the first to promote personal and environmental hygiene to prevent disease.

HISTORY The miasmatic theory of disease held that

diseases such as cholera or the Black Death were caused by a miasma (Greek language: "pollution"), a noxious form of "bad air". In general, this concept has been supplanted by the more scientifically founded germ theory of disease.

The development of a sufficiently powerful microscope by Anton van Leeuwenhoek in 1675 provided visual evidence of living particles consistent with a germ theory of disease.

HISTORY

John Graunt, a professional haberdasher and serious amateur scientist, published Natural and Political Observations ... upon the Bills of Mortality in 1662. In it, he used analysis of the mortality rolls in London before the Great Plague to present one of the first life tables and report time trends for many diseases, new and old.

He provided statistical evidence for many theories on disease, and also refuted many widespread ideas on them.

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.

.

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.

HISTORY Map of Cholera

outbreaks in London

HISTORY Other pioneers include Danish physician P. A.

Schleisner, who in 1849 related his work on the prevention of the epidemic of tetanus neonatorum on the Vestmanna Islands in Iceland.

Another important pioneer was Hungarian physician Ignaz Semmelweis, who in 1847 brought down infant mortality at a Vienna hospital by instituting a disinfection procedure. His findings were published in 1850, but his work was ill

received by his colleagues, who discontinued the procedure. Disinfection did not become widely practiced until British

surgeon Joseph Lister 'discovered' antiseptics in 1865 in light of the work of Louis Pasteur.

In the early 20th century, mathematical methods were introduced into epidemiology by Ronald Ross, Anderson Gray McKendrick and others.

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 Disease a pattern of response by a living organism

to some form of invasion by a foreign substance or injury which causes an alteration of the organisms normal functioning also – an abnormal state in which the body is not capable of

responding to or carrying on its normally required functions Pathogens organisms or substances such as

bacteria, viruses, or parasites that are capable of producing diseases

Pathogenesis the development, production, or process of generating a disease

Pathogenic means disease causing or producing Pathogenicity describes the potential ability and

strength of a pathogenic substance to cause disease

TERMS TO KNOW Infective diseases are those which the

pathogen or agent has the capability to enter, survive, and multiply in the host

Virulence the extent of pathogenicity or strength of different organismsthe ability of the pathogen to grow, thrive, and to

develop all factor into virulencethe 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 hostThe capacity of a microorganism o enter into and

grow in or upon tissues of a host

TERMS TO KNOWEtiology the factors contributing to the

source of or causation of a diseaseToxins a poisonous substance that is a

specific product of the metabolic activities of a living organism and is usually very unstable notably toxic when introduced into the tissues,

and typically capable of inducing antibody formation

Antibiotics a substance produced by or a semisynthetic substance derived from a microorganism and able in dilute solution to inhibit or kill another microorganism

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 KNOWepidemic: 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

Incidence =

# of New Cases Occurring in a Given Population in a Specified Time Period_

Population at Risk in That Time Period

(Speedometer)

TERMS TO KNOW

prevalence: the number of people within a population who have a certain disease at a given point in time

point prevalence: how many cases of a disease exist in a group of people at that moment.

prevalence relies on 2 factors:How many people have had the disease in

the pastDuration of the disease in the population

Prevalence =

# of Cases Existing in a Given Population at a Single Point in Time__ Population at That Time

(odometer)

7 USES OF EPIDEMIOLOGY1. 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 health2. 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 assessments4. 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

CLASSICAL VERSUS MODERN APPLICATIONS

Classical: descriptive, observational, field, analytical, experimental, applied, healthcare, primary care, hospital, CD, NCD, environmental, occupational, psycho-social, etc

Modern: risk-factor, molecular, genetic, life-course, CVD, nutritional, cancer, disaster, etc

BROAD TYPES OF EPIDEMIOLOGYBROAD TYPES OF EPIDEMIOLOGY

Examining the distribution of a disease in a population, and observing the basic features of its distribution in terms of time, place, and person. We try to formulate hypothesis, look into associations ?

Typical study design:

community health survey (synonyms: cross-sectional study,

descriptive study)

Testing a specific hypothesis about the relationship of a disease to a specific cause, by conducting an epidemiologic study that relates the exposure of interest to the outcome of interest (? Cause-effect relationship) Typical study designs: cohort, case-control, experimental design

DESCRIPTIVE EPI ANALYTIC EPI

THE EPIDEMIOLOGY TRIANGLE

Outbreaks in a population often involves several factor and entities

Many people, objects, avenues of transmission, and organisms can be involved in the spread of disease

Epidemiologist have created a model to help explain the multifaceted phenomena of disease transmission: the epidemiology triangle

THE EPIDEMIOLOGY TRIANGLE

Many diseases rely on an agent or single factor for an infectious disease to occur.

Epidemiologist use an ecological view to assess the interaction of various elements and factors in the environment and disease-related implications

When more than a single cause must be present for a disease to occur, this is called multiple causation

THE EPIDEMIOLOGY TRIANGLE

The interrelatedness of 4 factors contribute to the outbreak of a disease

1. Role of the host2. Agent 3. Environmental circumstances4. TimeThe epidemiology triangle is used to analyze

the role and interrelatedness of each of the four factors in epidemiology of infectious diseases, that is the influence, reactivity and effect each factor has on the other three

DESCRIPTIVE EPIDEMIOLOGY IS A DESCRIPTIVE EPIDEMIOLOGY IS A NECESSARY ANTECEDENT OF ANALYTIC NECESSARY ANTECEDENT OF ANALYTIC

EPIDEMIOLOGYEPIDEMIOLOGY

To undertake an analytic epidemiologic study you must first:

Know where to look Know what to control for Be able to formulate / test hypotheses

compatible with a-priori lab / field evidence

THE EPIDEMIOLOGY TRIANGLE

Time

BASIC TRIAD OF DESCRIPTIVE BASIC TRIAD OF DESCRIPTIVE EPIDEMIOLOGYEPIDEMIOLOGY

THE THREE ESSENTIAL CHARACTERISTICS OF DISEASE WE LOOK FOR IN DESCRIPTIVE EPIDEMIOLOGY ARE:

PERSONPLACETIME

PERSONAL CHARACTERISTICS PERSONAL CHARACTERISTICS (WHOM)(WHOM)

Age Gender Socio-economic status (education, occupation,

income) Marital status Ethnicity/race/genetic profile Behavior / habits

PLACE (WHERE ?)PLACE (WHERE ?)

Geographically restricted or widespread (outbreak, epidemic, pandemic)? Off-shore (tsunami…)

Climate effects (temperature, humidity, combined effects..)

Urban / sub-urban-squatter / rural   Relation to environmental exposure (water, food supply, etc)   Multiple clusters or one?

TIME (WHEN ?)TIME (WHEN ?)

Changing or stable?

Clustered (epidemic) or evenly distributed (endemic)?

Time-trends: Point source, propagated, seasonal, secular, combinations

INFECTIOUS CYCLE

THE EPIDEMIOLOGY TRIANGLE

Time

THE EPIDEMIOLOGY TRIANGLE The agent is the cause of the disease

Can be bacteria, virus, parasite, fungus, moldChemicals (solvents), Radiation, heat, natural

toxins (snake or spider venom) The host is an organism, usually human or

animal, that harbors the diseasePathogen disease-causing microorganism

or related substanceOffers subsistence and lodging for a pathogenLevel 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.

AGENTSAGENTS Biological (micro-organisms) Physical (temperature, radiation, trauma,

others) Chemical (acids, alkalis, poisons, tobacco,

others) Environmental (nutrients in diet, allergens,

others) Psychological experiences

HOST FACTORSHOST FACTORS

Genetic endowment Immunologic status Personal characteristics Personal behavior Definitive versus intermediate (in vector-

borne diseases)

THE EPIDEMIOLOGY TRIANGLE The environment is the favorable

surroundings and conditions external to the human or animal that cause or allow the disease or allow disease transmissionEnvironmental factors can include the biological

aspects as well as the social, cultural, and physical aspects of the environment

Time accounts for incubation periods, life expectancy of the host or pathogen, duration of the course of illness or condition.

THE EPIDEMIOLOGY TRIANGLE The mission of the epidemiologist is to break

one of the legs of the triangle, which disrupts the connection between environment, host, and agent, stopping the continuation of an outbreak.

The goals of public health are the control and prevention of disease.

By breaking one of the legs of the triangle, public health intervention can partially realize these goals and stop epidemics

An epidemic can be stopped when one of the elements of the triangle is interfered with, altered, changed or removed from existence.

ENVIRONMENTENVIRONMENT

Living conditions (housing, crowding, water supply, refuse, sewage, etc)

Atmosphere / climate Modes of communication: phenomena

in the environment that bring host and agent together, such as: vector, vehicle, reservoir, etc)

DISEASE TRANSMISSION Fomites: inanimate objects that serve as a

role in disease transmission Pencils, pens, doorknobs, infected blankets

Vector: any living non-human carrier of disease that transports and serves the process of disease transmission Insects: fly, flea, mosquito; rodents; deer

Reservoirs: humans, animals, plants, soils or inanimate organic matter (feces or food) in which infectious organisms live and multiply Humans often serve as reservoir and host

Zoonois: when a animal transmits a disease to a human

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.

DISEASE TRANSMISSION Active carrier: individual exposed to and harbors

a disease-causing organism. May have recovered from the disease

Convalescent carrier: exposed to and harbors disease-causing organism (pathogen) and is in the recovery phase but is still infectious

Healthy carrier: exposed to an harbors pathogen, has not shown any symptoms

DISEASE TRANSMISSION

Incubatory carrier: exposed to and harbors a disease and is in the beginning stages of the disease, showing symptoms, and has the ability to transmit the disease

Intermittent carrier: exposed to and harbors disease and can intermittently spread the disease

Passive carrier: exposed to and harbors disease causing organism, but has no signs or symptoms

MODES DISEASE TRANSMISSION

Modes of disease transmissionmethods by which an agent can be passed

from one host to the nextor can exit the host to infect another

susceptible host (either person or animal) Two general modes

direct indirect

Direct transmission or person to person Immediate transfer of the pathogen or agent

MODES DISEASE TRANSMISSIONDirect transmission or person to person

Immediate transfer of the pathogen or agent from a host/reservoir to a susceptible host

Can occur through direct physical contact or direct personal contact such as touching contaminated hands, kissing or sex

Indirect transmissionpathogens or agents are transferred or carried by

some intermediate item or organism, means or process to a susceptible host

done in one or more following ways: airborne, waterborne, vehicleborne, vectorborne

MODES DISEASE TRANSMISSION Indirect transmission

Airborne Droplets or dust particles carry the pathogen to the host

and infect it Sneezing, coughing, talking all spray microscopic droplets

in the air Waterborne

Carried in drinking water, swimming pool, streams or lakes used for swimming. Examples: cholera

Vehicleborne Related to fomites

Vectorborne A pathogen uses a host (fly, flea, louse, or rat) as a

mechanism for a ride or nourishment this is mechanical transmission

biological transmission when the pathogen undergoes changes as part of its life cycle, while within the host/vector and before being transmitted to the new host

CHAIN OF TRANSMISSION Close association between the triangle of

epidemiology and the chain of transmission Disease transmission occurs when the pathogen or

agent leaves the reservoir through a portal or exit and is spread by one of several modes of transmission.

Breaks in the chain of transmission will stop the spread of disease

Etiological agent/pathway Source /

Reservoir

Mode of transmission

Host

CLASSES OF EPIDEMICS / OUTBREAKSCommon Source Epidemic – when a group

of persons is exposed to a common infection or source of germsPoint source from a single source (food)

Persons exposed in one place at one time and become ill within the incubation period

Ex: bad mayonnaise at a picnicIntermittent irregular and somewhat

unpredictable Tuberculosis spread by person to person contact and

people move around and interact with other peopleContinuous epidemic

When an epidemic spreads through a community or population at a high level, affecting a large number of people within the population without diminishing

CLASSES OF EPIDEMICS / OUTBREAKS Propagated Epidemic when a single source

cannot be identified, yet the epidemic or diseases continues to spread from person to person Usually experiences exponential growth Cases occur over and over longer than one incubation

period Mixed Epidemic a common source epidemic is

followed by person-to-person contact and the disease is spread as a propagated outbreak

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

IMMUNITY AND IMMUNIZATION History

Before polio vaccine became available in 1955, 58,000 cases of polio occurred in peak years. ½ of these cases resulted in permanent paralysis

Prior to measles vaccine in 1963, 4,000,000 cases per year

Immunization of 60 million children from 1963-1972 cost $180 million, but saved $1.3 billion

Mumps used to be the leading cause of child deafness

10% of children with diphtheria died

IMMUNITY AND IMMUNIZATION According to CDC, unless 80% or greater of the

population is vaccinated, epidemics can occur Three types of immunity possible in humans

Acquired Immunity obtained by having had a dose of a disease that stimulates the natural immune system or artificially stimulating immune system

Active Immunity body produces its own antibodies can occur through a vaccine or in response to having a similar

disease Similar to acquired

Passive Immunity (natural passive) acquired through transplacental transfer of a mother’s immunity to diseases to the unborn child (also via breastfeeding) can also come from the introduction of already produced antibodies

into a susceptible case

IMMUNITY When there is little

to no immunity within a population, the disease spreads quickly

IMMUNITYHerd Immunity the resistance a

population or group (herd) has to the invasion and spread of an infectious disease

DISEASES FOR WHICH VACCINES ARE USED

Antrhax Chicken pox Cholera Diphtheria German measles

(rubella) Hepatitis A & B Influenza Malaria (in process) Measles Menigitis Mumps Plague

Pneumonia Polio Rabies Small pox Spotted fever Tetanus Tuberculosis Typhoid Fever Typhus Whooping Cough Yellow Fever