Epidemiology

Epidemiology

the study of how diseases occur and spread in groups of people and how we can prevent and control them

like being a detective for health and figuring out who gets sick, why, where, and how to stop it

Nursing Process

client based

assessment → individual client database established and data is interpreted 

diagnosis → healthcare needs and assets are identified and goals/objectives for care are established 

planning → processes for achieving goals are selected 

implementation → actions initiated to achieve goals

evaluation → extent of goal achievement is determined 

Epidemiology Process

population based

assessment → data is gathered from reliable sources/nature, extent, and scope of problem are defined and problem is described by person, place, time

diagnosis → tentative hypothesis formulated and data analyzed to test the hypothesis

planning → plans are made for control and prevention of condition/event

implementation → actions initiated to implement the plan

evaluation → actions evaluated and report is prepared and further research is conducted if necessary

Analytic Epidemiology

goal is to discover the determinants of health outcomes and the how and why

deals with factors that influence the observed patterns of health and disease and increase/decrease the risk for adverse outcomes

identify causative agents and identify characteristics of the agents

determine the mode of transmission

identify geographic patterns

determine contributing factors

involves hypothesis testing

ex: cohort studies, case control studies, cross sectional studies, and ecologic studies

Cohort Studies

refers to a groups of persons generally sharing some characteristics of interest

enrolled in a study and followed over time to observe some health outcome

allow for calculation of incidence rates and it estimates the risk of disease

Prospective Cohort Studies

subjects who do not have the outcome under investigation are classified on the basis of the exposure of interest at the beginning of the follow up period

subjects are then followed for a period of time to determine the occurence of disease in each group

Retrospective Cohort Studies

rely on existing records to define a cohort that is classified as having been exposed or unexposed at some time in the past

they are followed over a period of time using records to determine if the outcome occurred 

Case Control Studies

subjects are enrolled because they are known to have the outcome of interest (these are cases) or they are known to not have the outcome of interest (controls)

Cross Sectional Studies

provides a snapshot or cross section of a population or group

info is collected on current health status, personal characteristics, and potential risk factors or exposures all at once

there is simultaneous collection of info necessary for the classification of exposure

Ecological Studies

bridges descriptive and analytical epidemiology

the descriptive component looks at the variation in disease by rates by person, place, or time

the analytic component tries to determine if there is a relation of disease rates to variations in rates for possible risks 

Descriptive Epidemiology

describes the distribution of disease, death, and other health outcomes in the population according to person, place, and time

what is the health event, disease, and what is the outcome

who is at risk or who is ill (person)

where did the health event occur (place)

when did the health event happen and how long did the illness last (time)

ex: counts, ratio, proportion, risks, rates

Counts

simplest measure to describe how many cases 

Ratio

fraction that represents the relationship between two numbers or counts

value obtained by dividing one quantity by another

people or things counted in the numerator are not counted in the denominator

Proportion

type of ratio that includes the quantity in the numerator as part of the denominator → relationship of parts to a whole

meaning the relationship between counts because the numerator is parts of the whole (denominator)

Risks

refers to the probability that an event will occur within a specified period

a population at risk is the population of people for whom there is some finite probability of that event occurring 

Rates

primary measurement used to describe the occurence (frequency or quantity) of a state of health in a specific group of people in a given period of time

best indicators of risk (probability) that a specific disease, condition, or event will occur

rates are used to quantify the occurence (incidence) of the existence (prevalence) of the states of health or illness

using this rather than counting cases take both the size of the population at risk and the time frame into account

Adjusted Rate

statistical procedure that removes the effects of differences in the composition of a population like age when comparing one another

Attack Rate

same as the incidence rate 

Crude Rate

the number of occurrences compared to the entire population

Fatality Rate

the proportion of persons diagnosed with a particular disease and die within a specified period

considered an estimate of the risk for death within that period for a person newly diagnosed with the disease

Mortality Rate

known as the death rate

the measure of the number of deaths in a population per unit of time relative to the populations size

typically expressed as the number of deaths per 100 people per year

Epidemiologic Models

epidemiologic triad/triangle

chain of infection model

wheel of causation model

web of causation model

Epidemiolog Triad

intrinsic factors → host

extrinsic factors → agent and environment

Host

a susceptible human or animal who harbors and nourishes a disease causing agent

many physical, psychological, and lifestyle factors influence the hosts susceptibility and response to the agent

modifiable → lifestyle, exercise, nutrition, health knowledge, motivation for achieving optimal wellness

non-modifiable → age, race, genetics 

Agent

factor that causes or contributes to a health problem or condition

agents vary considerably and includes

physical → heat, cold, radiation

chemical → pollutants, meds, drugs, heavy metals, pesticides

nutritional → absence or excess water, vitamins, fats, protein, carbs

psychosocial → stress, social isolation, social support

biologic → bacteria, viruses, arthropods, toxins, fungi, parasites

Environment

refers to all the external factors surrounding the host that might influence vulnearability or resistance and includes

biologic → composed of plants, animals, and toxins they produce, pathogenic microorganisms, vectors, reservoirs

physical → light, air, atmospheric pressure, radiation, geologic factors, structures in the environment

social → culture, technology, educational opportunities, political systems, demographic characteristics, sociologic factors, economic, legal systems

Epidemic

occurrence of disease in excess of normal expectation (ex: outbreak of measles in NYC) 

arise when host, agent, and environmental factors are not in balance

new agent

change in existing agent (infectivity, pathogenicity, virulence)

change in the number of susceptible hosts in the population

environmental changes that affect transmission of growth of agent

Endemic

constant and persistant presence of disease in a geographic region or population

ex: malaria in africa

Sporadic

problems with an irregular pattern

occasional cases at irregular intervals

ex: food borne illnesses

Hyperendemic 

persistently high number of cases 

ex: lyme disease in NJ

Pandemic

epidemic spread of disease across geographic regions, countries, or continents 

ex: SARS and COVID-19

Acquired Immunity

resistance to infectious agent developed from previous exposure from disease or immunization

ex: active, passive, cross 

Active Immunity

administration of an antigen that can produce an antibody (vaccinations) providing more long term resistance

Passive Immunity

transfer of specific antibody that provide short term resistance

immunoglobulins such as HepA, rabies, tetanus

antiserum like ebola and snake antivenom

breast milk

Cross Immunity

immunity to one agent provides a person with immunity to another agent

Natural Immunity

innate resistance to infectious agent

Herd Immunity

immunity level present in a population that has a protective effect on the population

Chain of Infection

agent/microorganisms 

reservoir

portal of exit

modes of transmission

portal of entry

susceptible host 

Agent

disease producing (pathogens_

risks → virulence, pathogenicity, infectivity

Reservoir

environment or habitat where agent can live and multiple

ex: humans or animals

Exit Portal

how the pathogen exists or leaves reservoir

skin to skin, skin to surface, blood, mucus membranes

oral cavity, fecal, urine, seminal fluid, saliva

Transmission Modes

pathogen moves from reservoir to susceptible host

direct → airborne, droplet, contact, bite, needlestick

indirect → fomites (inanimate), vectors, food, water

Entry Portal

opening where the pathogen may enter

body openings (mouth, eyes, urinary tract, respiratory tract, incisions, wounds)

Susceptible Host

the person at risk

factors → age, health, comorbidities, immune system

Immunogenicity

ability of the agent to produce specific immunity within the host

Infectivity 

ability of an infectious agent to invade the host and replicate

Invasiveness

ability of the agent to destroy healthy tissue

Pathogenicity

ability of an infectious agent to cause damage in a susceptible host

Toxicity

ability of the agent to produce toxins

Virulence

severity of damage caused by the infectious agent

Mechnical

uninfected insect carries the agent

ex: fly picks up pathogen from fecal matter and carries it on its body, fly transfers pathogen to food, person eats contaminated food and gets sick

Biological 

infected insect carries pathogen

ex: infected mosquito bites uninfected person, infection spreads through body and into RBC, second mosquito bites infected person and the mosquito may now transmit infection to another person

Vector Borne

transmission via insect

Wheel of Causation

many disease, illnesses, and condition have multiple or no discernible agents or the agent may be a part of the environment

alternate model is conceptualized as a wheel with a circle as the genetic core of the host, surrounded by a larger segmented wheel representing the biologic, physical, or social environments

model de-emphasizes the agent as the sole cause of disease where it emphasizes the interplay of physical, biologic, and social environments

interaction between host and environment with or without an identifiable agent remains the major determinant of health status in all epidemiologic models

Web of Causation

strongly emphasizes the concept of multiple causation while de-emphasizing the role of agents in explaining diseases

helps describe the multiple complex and interrelated factors underlying chronic illnesses

necessary to identify all possible factors that could influence the development or prevention of a particular health condition

each factor is perceived as a link in multiple interrelated chains

direct and indirect factors can be identified that can be changed or modified to improve health

provides multiple entry points for intervention but also has the capacity to demonstrate the interrelationship of different factors that can include predicted and unpredicted side effects

used to design methods that interrupt the chain of events that lead to adverse states of health

Incidence Rate

measure of the probability that people without certain conditions will develop the condition over a period of time, often a year

measures the pace at which new illnesses like COVID occur in a previously disease free group of people

the calculation counts only the new cases that have occurred in the designated time period are counted and placed in the numerator

the risk

how widespread a disease is, includes old cases, point in time (snapshot)

Calculating Incidence Rate

all the events (cases) being measured should be in the numerator

everyone included in the denominator should be at risk for the event in the numerator

specific period of time for the observation must be clearly indicated, can range from a single point in time to several years depending on the type of rate being calculated

rate is a fraction or proportion so its necessary to multiply by a base usually a multiple of ten to make the rates understandable

removes the decimal points and makes the comparison of rates easier to interpret, any base multiple of ten may be chosen that results in a rate above the value one and for larger pops use 100,000 and small use 100

rate = number of conditions (cases) within a designated period of time divided by population at risk during the same period of time (multiply by constant K)

Incidence 

tells us how many new cases of a disease occur in a population during a specific time period

number of new cases/population at risk (multiply by 1000)

Prevalence Rate

measures the number of people in a given population who have existing condition at a specific point in time

both new cases and existing cases are counted in the designated time period and placed in the numerator

the burden

tells us how common a disease or condition is at a certain point in time or over a period of time

number of existing cases/total population (100)

how many new cases develop, no old cases, over time (movie)