Module 10 Flashcards
Epidemiology
The investigation of how health events in a population are patterned or distributed
Purpose of Epidemiology
Purpose is to provide a basis for developing:
- prevention strategies for groups at risk
- disease control measures for affected groups
Descriptive Epidemiology
concerned with WHAT WHO WHERE and WHEN
Focuses on the frequency and distribution of states of health within a population
*focus of this class
Analytic Epidemiology
concerned with HOW and WHY
Examples of What in Descriptive Epidemiology
What is the health event
what is the disease
what is the outcome
how severe is it
Examples of Who in Descriptive Epidemiology
Who are at risk
who is ill
(person)
Examples of Where in Descriptive Epidemiology
Where did the health event occur
How widespread is the illness
(place)
Examples of When in Descriptive Epidemiology
When did the health event happen
how long did the illness last
(time)
Characteristics included in the WHO/person of descriptive epidemiology
Age, gender, ethnicity
genetic predisposition
concurrent disease
diet and exercise
risk taking behaviors such as smoking
socio economic status
marital status
education and occupation
Characteristics included in the WHERE/place of descriptive epidemiology
Presence of agents or vectors
climate and geography
population density
economic development
customs and practices of the area
medical care and access
regional crime and unemployment rates
Characteristics of the WHEN/time of descriptive epidemiology
Calendar time
time since an event
physiologic cycles
age (time since birth)
seasonality
temporal trends
Basic Measures of Descriptive Epidemiology
Counts
Ratio
Proportion
Attack Rate
Prevalence
Prevalence Rate
Counts
simplest measure to describe how many cases
ex: 20 colds occurred
Ratio
relationship between two counts, numerator is not included in the denominator
(# those that are ill, divided by [compared to] # those that are not)
ex: 1:3 ratio of sick to healthy
Proportion
relationship between two counts
numerator is included in the denominator, part of a whole
(# of those that are ill divided by everyone)
ex: 20/100
Attack Rate
Number of persons that develop a disease divided by the number of persons exposed to the causative agent (used commonly in food Bourne illness investigations or flu outbreaks)
ex: Developed/Exposed = 5 w food poisoning / 20 total exposed
* exposed includes those who developed disease
Prevalence
Number of cases of a disease or health condition divided by the total population at a particular time
cases / total pop at a certain time
Prevalence Rate
(# of cases / population at a time) x K (constant that is 1000 or 10000)
allows for comparisons between groups or regions on a certain date!!!
something may seem worse initially but the prevalence rate can reveal that is not always the case
Incidence Rate
(# of cases / population at RISK) x K at a certain time
People who die from a disease or become immune to the disease fall out of the population at risk!!!
People who die from a disease or who recover from a disease fall out of the pool of prevalent cases because they no longer are counted as having the disease
Prevalence is a function of the ____ of disease and the ____ of disease
Incidence and Duration
A town has a population of 3600.
In 2003, 400 residents of the town are diagnosed with a disease.
In 2004, 200 additional residents of the town are diagnosed with the same disease. The disease is lifelong but it is not fatal.
calculate the prevalence in 2003?
calculate the prevalence In 2004?
calculate the incidence in 2004?
K=1000
2003 - 400/3600 x 1000 = 111 per 1000
2004 - 600 / 3600 x 1000 = 167 per 1000
Incidence of 2004: 200/3200 x 1000 = 63 per 1000
Analytic Epidemiology
Focuses on the CAUSES AND ASSOCIATIONS of states of health within a population (HOW AND WHY)
Things Identified or Determined in Analytic Epidemiology
ID causative agents, characteristics of agents, geographic patterns
Determine mode of transmission, contributing factors
involves hypothesis testing
3 Essential Characteristics examined in analytic epidemiology to determine how and why are …
Agent
Host
Environment
(The epidemiological triangle)
Agent
bacteria, virus, fungi, parasite
Host
human or animal harboring agent
Environment
physical, biological, social, and cultural factors facilitating the transmission of the agent from host to host
Early influence on epidemiology came from….
religion
Hippocrates and Epidemiology
first looked at health and disease from environmental and behavior perspectives
Miasma Theory
poisoning from foul vapors
Edward Jenner and Epidemiology
“Father of Immunology”
1798
Demonstrated small pox vaccination effectiveness
Germ Theory
microorganisms cause disease
John Snow and Epidemiology
1850
ID source of cholera epidemic to contaminated well in london
Florence Nightingale and Epidemiology
1850s
examined and tracked environmental conditions to recovery rates of soldiers in the crimean war
Chronic Disease Epidemiology
outcomes related to exposure
modifying behavior can control risk factors
Human Genome Project
New bio medical technologies can examine genetic risks
3 Important Triumphs in Epidemiology
- Small pox eradication thru vaccinations in 1967 to 1980 when it was declared dead by WHO
- cig smoking found to be major lung cancer, emphysema, and CV disease cause 1951-1963
- ID of auto immune deficiency syndrome (AIDS) and predicted that cause from STI. Development of prevent measures before the virus was ID’ed - 1981-1983
5 Important Epidemiologic Models
- Epidemiologic Triangle
- Wheel Model
- Web of Causation
- Chain of Infection
- Stages of Disease (natural history of disease)
Epidemiologic Triangle
most simple epidemi model
Factors that influence health status are:
- intrinsic Factors (host factors)
- Extrinsic factors (agent and environment)
The epidemiologic triangle occurs …
over time
Host Factors
Intrinsic factors that are the hosts ability to resist a particular infectious disease causing agent (the body forms antibodies that react with a foreign antigen and makes them harmless)
Examples of Host Factors
Genetic Susceptibility
Immutable characteristics: age, gender, race, sex
Acquired characteristics: immunological status
lifestyle factors
immunity status
Acquired Immunity
resistance to infectious agent developed from previous exposure from disease or immunization
Can be active passive or cross
Active Immunization/Immunity
Administration of an antigen that can produce an antibody (vaccinations) providing more long term resistance
type of acquired immunity
Passive Immunization/Immunity
transfer of specific antibody that provides short term resistance
type of acquired immunity
ex: immunoglobins (Hep A, Rabies, Tetanus); Antiserum (Ebola, Snake Anti Venom); Breastmilk
Cross immunity
immunity to one agent provides a person with immunity to another agent
ex: Edward Jenner noticed that milkmaids exposed to cow pox did not get small pox
Natural Immunity
innate resistance to infectious agent
Herd Immunity
immunity level present in a population that has a protective effect on the population
Extrinsic Factor Types
Biological
Chemical
Physical
Nutrient
Genetic
Psychological
Biological Agent
bacteria
virus
fungi
parasite
Chemical Agent
heavy metals
toxic chemicals
pesticides
Physical Agents
radiation
heat and cold
machinery
Nutrient Agent
basic dietary components needed to survive
Genetic Agent
Transmitted from child to parent through genes
Psychological Agent
stressful circumstances in the environment
Important characteristics of Extrinsic Agents?
Infectivity
Pathogenicity
Virulence
Infectivity
ability of agent to multiply, enter the host, and produce disease
Pathogenicity
measures the proportion of people who develop the disease after infection
Virulence
ability of agent to produce a pathological reaction resulting ins severe disease or death
Herd Immunity is note necessarily a ___ factor, it is partly a ____ factor
host; environmental
Environmental Factors
Extrinsic
- Physical (Climate)
- Biological Environment (living plants, animals, human pop distrib)
- Socioeconomic Factors (working conditions, codes, laws, herd immunity)
Wheel model of causation
used to investigate:
acute and chronic diseases
infectious and non infectious processes
why some populations stay healthy while others become ill
Compartments and their Sizes in the Wheel Model of Causation
Genetic Core surrounded by the Host (human)
3 sections of social environment, biological environment, and physical environment surround it
The relative size of the various compartments change depending on the specific problem under consideration
Patterns of Disease
Epidemic
Endemic
Sporadic
Hyperendemic
Pandemic
Epidemic
Occurrence of disease in excess of normal expectation
arises when:
- host, agent, and environmental factors are not in balance
- new agent
- change in existing agent (infectivity, pathogenicity, virulence)
- change in number of susceptible hosts in the population
- environmental changes that affect transmission of the agent or growth of the agent
Endemic
constant and persistent presence of disease in a geographic region or population (ex: malaria in africa)
Sporadic
problems with an irregular pattern; occasional cases at irregular intervals (food borne illness)
Hyperendemic
persistently high number of cases (lyme disease in new jersey)
Pandemic
epidemic spread of disease across geographic regions, countries, or continent’s (SARS to canada and the US)
Web of Causation
model that shows direct and indirect causal relationships
displays more complex interrelationships that can increase or decrease the risk of disease!!!
*can get very complex among multiple things like cardiovascular disease for example
Direct Causal Associations
no intermediate factor and is more obvious
ex: exposure to staph pathogens results in illness
Indirect Causal Associations
involves one or more intervening factors and is often much more complicated
ex: a high fat diet is assoc with polyps and polyps are associated with colon cancer
Web of Causation model States that…
- Disease never results from a single cause
2. disease develops as a result of chains of causation
Web of Causation model is used when …
A complete understanding of the causal mechanism is not prerequisite to the development of effective measures of prevention or control
Chain of Infection
Infectious Agent –> Reservoir –> Portal of Exit –> mode of Transmission –> portal of entry –> susceptible host –> infectious agent repeat
Reservoir
dont confuse with host
habitat in which an infectious agent usually lives, grows, and multiplies
can include animals, humans, and the environment
may or may not be the source from which an agent is transmitted
Human Reservoirs
Also known as “Carriers”
carriers are persons that may be asymptomatic but capable of transmitting the agent to others
chronic carrier continuously harbors an agent (Hep B, Typhus) after an initial infection
Zoonoses
animal reservoirs
animals can be host, vector, or source of certain infections and disease
Zoonosis/zoonoses is an infectious organism in VERTEBRATE animals that can be transmitted to humans through direct contact, fomite, or vector
The word comes from Zoon (animal) Noses (Ill)
ex: rabies, cat scratch fever
Other than zoonoses, what else is an animal reservoir?
diseases transmitted by (vector) insects (ex; lyme disease)
Environmental reservoirs
can be vehicle or airborne for example\
plant, soil, water (ex: e coli and tetanus)
Examples of the many diseases that are zoonoses
Aids Amebiasis Anthrax Bovine Papular Stomatitis Brucellosis California Encephalitis Cat Scratch Fever colorado tick Fever Cowpox Dengue Fever Dermatophilosis Leprosy Lyme Disease Pasteurellosis Plague Q Fever Rabies Rat Bite Fever Rickettsial Pox Rocky mounntain spotter fever salmonellosis shigellosis streptococcus infections tetanus trichinosis tularemia yellow fever zoonotic scabies
Portal of Entry
the path by which agent enters susceptible host
usually the same portal they exit (ex: TB and flu)
others include: skin and the mucus membrane
Enteric Pathogenic Atgents
“Fecal-Oral” portal of entry agents
Portal of Exit
the path by which an agent leaves the source
usually corresponds to the site at which the agent is localized (eg TB and flu) exit the respiratory tract
some blood borne agents can exit by crossing the placenta (ex: rubella and syphilis)
Common Portals of Entry/Exit
respiratory
oral
reproductive
intravenous
urinary
skin
gastrointestinal
conjunctival
transplacental
Modes of Transmission
Vertical
Horizontal (Direct or Indirect [vehicle, vector, airborne])
Vector (mechanical or biological)
Vertical transmission
passing of infection from parent to offspring
ex: sperm, placenta, breastmilk, contact in vaginal canal during birth
Horizontal Transmission
person to person spread
can be direct or indirect
Direct Horizontal Transmission
direct contact
droplet spread
(touching, kissing, biting, sexual intercourse, coughing, sneezing, large droplets in close proximity)
Indirect horizontal Transmission
can be vehicle, vector, or airborne
Vehicle Borne Indirect Horizontal Transmission
nonliving intermediary such as a fomite, food, water, or infectious bodily fluids that convey the infectious agent from the reservoir to a susceptible host
Vector Borne Transmission
transmission via insect (mosquitoes, flies, ticks, spiders)
Does not cause disease but transmits it to the susceptible host
can be mechanical vector or biological vector
Airborne Indirect Horizontal Transmission
transmitted via dust and fine particles known as aerosols
ex: TB, legionnaires, influenza
Fomite
an inanimate object contaminated with the infectious agent
Mechanical Vector
uninfected insect carries the agent
Biological Vector
infected insect carries pathogen
Natural history of Disease (Stages of Disease over Time)
- Stage of Susceptibility
- Preclinical or Presymptomatic Stage
- Clinical Stage
- Stage of Recovery, Disability, or Death
Stage of Susceptibility
first stage
no disease present (pre-pathogenesis)
Preclinical or Presymptomatic stage
second stage
biological onset, no signs or symptoms (pathogenesis)
there is an incubation and latency period within this
Clinical Stage
third stage
signs and symptoms, medical care is sought, diagnosis is made (pathogenesis)
Stage of Recovery, Disability or Death
stage 4
treatment (resolution)
Primary Prevention can help in what part of the natural course of disease
susceptible hosts pre-exposure
Secondary Prevention can help in what part of the natural course of diseases
Subclinical Disease Stage to clinical illness stage
Tertiary Prevention can help in what part of the natural course of disease
stage of recovery, disability, or death
Subclinical Disease Stage marks…
the beginning of pathological process and changes within the body
it is then followed by onset of symptoms then diagnosis sought which is then followed by the clinical illness stage
