Ch 16: Epidemiology Flashcards
Epidemiology
Is the science of the cause, prevalence and spread of disease
Disease is a codition that negatively affects teh structure or function of all or part of an organism
What is the purpose of epidemiology
concerned with the geographical distribution of disease, the route of transmission, the maintenace of the disease in a population and practical methods to control or prevent outbreaks
Morbidity
state of being diseased
Morbidity rate
the number of diseased people in a population
usually / 100 000
Prevalence`
The number of pople with a particular disease in a population at a point in time
incidence
the number of new cases in a period of time
Mortality
the death of an individual
Mortality rate
the number of deaths in a population
usually / 100 000
Case-Fatality rate
the proportion of deaths due to a disease compared to the numner of diagnosed cases
What are the patterns of incidence
Sporadic
Endemic
Epidemic
Pandemin
Common source epidemic
Point source epidemic
Continuous common source spidemic
Propagated epidemic
What is the sporadic pattern of incidence
observed occasionally with no specific geographical location
What is the endemic pattern of incidence
disease present constantly in a geographical location, usually at a low prevalence rate
What is the epidemic pattern of incidence
a large or larger than normal number of cases in a short period of time in a specific geographical location
What is the pandemic pattern of incidence
an epidemic that occurs on several continents
Common source epidemic
there si a single source for all cases on infection
Point source epidemic
a common source epidemic where the source is limited in time, usually about the incubation period of the disease
Continuous common source epidemic
the source exists for an extended period of time
Propagated epidemic
person to person spread without there being a single source
Etiology
the study of the origin (of a diease in this case)
The ideaa that an infection disease is caused by a livign agent (germ theory)
Types of Epidemiological Studies
Observational
Descriptive
Retrospective
Prospective
Cohort
Case control
Cross sectional
Case Crossover
Observational Study
Signs and symptoms and personal data collected from (usually) a random selection of patients
no experimental manupulation
demonstrates only associations between disease and causative agents
Descriptive study
collects information about patients,disease signs and symptoms and daata about their lives whihc may have bearing
interviews and medical records
Retrospective study
data from the past applied to disease cases today
Prospective study
collect data from a group of people before anyone contracts the diease
Cohort
A group of people who ahare a common characteristic such as age
Case control
usually retrospective comparison between a group of people with the disease agaisnt a group of people who do not have the disease
cross sectional
compares randomly selected individuals with and without the disease at a single time point
to determine a characteristic that is associated with disease
case crossover
each case of the disease is its own control
study each case during a time before disease and compare to after disease
Odds Ratio
relative odds
a measurement of association used in case control studies
OR= (a/b) / (c/d)
a= number of exposed cases b= the number of exposed controls c= the number of not-exposed cases d= number of not-exposed controls
OR = 1
no association between exposure and outcome (disease)
OR > 1
there is a positive association between exposure and outcome
Risk Ratio
relative risk
a measurement of association used in cohort studies
RR = [a/(a+b))] / [c/(c+d)]
a= number of exposed cases b= the number of exposed controls c= the number of not-exposed cases d= number of not-exposed controls
RR = 1
no association between exposure and outcome (disease)
RR >1
postivie association
RR <1
negative association
Attack rate
the cumulative percentage of people who get a diease over a period of time
the amount of people that aquire influenza over the course of the cold season
Experimental studies
studies in a laboratory or slinical setting where the investigator manupulates a variable
Koch’s postulates often used in experimental studies
Koch’s Postulates
The suspected pathogen must be found in evvery case of teh disease and not be found in healthy individuals
the suspected pathogen must be isolated and grown in pure culture
When teh suspected pathogen is inoculated into a healthy subject the disease must occur
The suspected pathogen must be re-isolated from this host and be identical to the original state
Modes of disease transmission
reservoirs
carrier
asymptomatic carrier
tranmission
contact transmission
Fomite or indirect contact transmission
vehicle transmission
airborne transmission
vector transmission
nosocomial infections
Reservoirs
the place or host where a pathogen normally resides
non-living reservoir such as soil or water
living reservoir such as an animal (bubonic plague in fleas of rodetns)
Carrier
an individual who can transmit a pathogen but may or may not display symptoms of the disease
same host can be the reservoir and the carrier
Asymtomatic carrier
an individual who can transmit a pathogen but does not display symptoms of the disease
Transmission
movement of the pathogen from reservoir to host or between hosts
successful entry of pathogen inot or onto a new host after transmission is infection
Contact transmission
Host to host movement of the pathogen by physical contact between two hosts Ex) -touching -sexual intercourse -droplet sprays -usually involves mucous membranes
Fomite or indirect contact transmission
Fomite is an inanimate object
Fomite becomes contaminated with the pathogen from one host then another host is infected from the object
ex)
Doorknob, cellphone, cutlery, towels and bedding, surfaces such as bed railings in hospitals
Vehicle Transmission
Vehicle = food and water
mostly gastrointestinal tract infections
also known as fecal-oral transmission
Airborne transmission
large droplets of water do not remain airborne for long
Droup out onto surfaces and then are touched by a host -> indirect contact transmission
The smaller the droplet, the longer it remains airborne and the more likely it can penetrate the host respiratory tract
5um or greater fall out of the air quickly and particles smaller than 5um remain airborne almost indefinitely
particles up to 20um may flow with air currents, ex) air conditioning for a distance then fall out.
Vector Transmission
Transmission of the pathogen by a living organism
mechanical transmission is transmission by a living organism without that organism being infected (flies)
Biological transmission is where the pathogen reproduced in the vector organism
ex) arthropods that bite = yellow fever and malaria in mosquitoes, lyme diseaase and ticks
Amplification vector
pathogen reproduces within the vector
liek malaria
Nosocomial infections
infections aquired in a heath care setting or through the delivery of health care (iatrogenic infection)
also called a Hospital aquired infection (HAI)
usually defined as infections aquired in a health care setting whihc manifest a cartain time after admission (24-72 hrs)
can be more serious than community aquired (CA) infections
antibiotic resistant bacterial infections
how long does it take to classify an infection as a nosocomial infection
24-72 hrs
Symptom
subjective changes or conditons reported by the patient
signs
objective changes or measurements
can be observed/ measured by outside observer
Disease syndrome
signs and symptoms plus laboratory tests
test = petri, antibodies, WBC count, Crp count etc…
Incubation time
time between infection and the start of reportable/ definative symptoms or signs
hard to know in a patient, because its hard to tell what was the initiating event.
Prodromal stage
indicaiton that a disease is present but without enough diagnosis signs and symptoms
fever, chills, myalgia, malaise
Illness period
Definite, diagnostic signs and symptonms, dieaase at its worst in the patient
Convelecense
symptoms are mild but you are not back to 100%
this comes after the illness period
Mortality rate
deaths/ population
need to use an adjusted mortality rate when comparing different countries (different people will die of different things at different ages)
Crude mortality rate
deaths/ population/ year
Top causes of mortality in Canada (2005)
/100 000
CVD 31%
Malignant neoplasms (cancer) 29%
Chronic respiratory diseases (also includes non-infections agents like asthma or emphesima) ~5%
Accidents 4.1%
diabetes
liver and kidney diseases
alzhiemers
Pregnancy, childbirth and perinatal
intential self-harm
influenza and pneumonia 2.5%
Tuberculosis
TOp causes of mortality in Canada due to infectious agents
Septicaemia// Septic shock
Intestinal infections (rotavirus, e. coli, salmonella, shingella etc…)
HIV
Hepatitis
other infectious and parasitic diseases (malaria and others)
Who regions
Americas
Western Pacific
Eastern mediterranean
South-east asia
europe
africa
The three main causes of death
CVD 1/3
Cancer 1/3
Everything else 1/3
children and young people die of
infectious diseases
the elderly die of
degenerative diseases
