Epi Classes 1 & 2 Flashcards
“The Epidemiologic Transition”
The disease of concern to populations are constantly shifting.
A population shift in disease and mortality patterns in high income countries:
- before transition (low income countries): most deaths from infection and malnutrition; high infant mortality rates; short life expectancy.
-after transition (high income countries): most deaths from heart disease, cancers and stroke; low infant mortality rates; long life expectancy
20th century epi
Refinement of epidemiological methods: outbreak investigation, study design for chronic diseases, clinical trials, biostatisical analysis
Cigarette smoke found unhealthy (1951-1963)
Eradication of smallpox (1978)
Increased focus on chronic disease and not just infectious disease/life expectancy
Analytic Epidemiology
“Agent” “Host” “Environment”
Why?/How?
Looks for causes/test hypotheses
Arthropod vectors
Bugs like mesquitos that carry disease. Discovered in 19th century as a carriers for diseases such as malaria, yellow fever, sleeping sickness and typhus
Asymptomatic Carrier
Person that carries and spreads disease but shows no symptoms. Discovered in 19th century as a contributor to disease spread.ex. typhoid mary
Bernardo Ramzzini
1633-1714: published comprehensive “disease of workers” detailing environmental hazards for 52 occupations.
Bias
An over or underestimation of something (value, factor)A miscalulation by the system
Case Fatality Rate (CFR)
deaths from a specific cause/# with the specific disease
The proportion of reported cases of a specified disease or condition which are fatal within a specific time.
CFR is a measure of the severity of a disease
Cohort
A group of people that can be followed over time
Criteria for a Risk Factor
- The frequency of disease varies by category or value of the exposure
- The risk factor (exposure) precedes the onset of the disease
- The observed association is not due to any source of error
- Association does not equal Causation
Descriptive Epidemiology
“Person” “Place” “Time”
Who? Where? When?
Disablity-Adjusted Life Year (DALY)
Measure of overall disease burden, expressed as the number of years lost due to ill-health, disablity or early death
Edward Jenner
1798: developed smallpox inoculation. Took cowpox and injected it into an 8 year old. After multiple injections over time, he was unable to catch smallpox
Efficacy
The abliity of an intervention to achieve the desired results under ideal conditions
Endemic
A disease or condition normally found in a population.
An infection is said to be endemic in a population when it is maintained without the need for external input
Epidemic
Higher than normal (baseline) incidence rates in a population.
A widespread occurance of an infectious disease in a community at a particular time
Health
A state of complete physical, mental and social well-being and not merely an abscense of disease or infirmity
Health Research
Examines the biological, socio-economic and environmental factors that contribute to health, disease, illness, diability and death
Henle-Koch Postulates
- The agent must be present in every case
- One agent = one disease
- Exposure of healthy subjects to suspected agents results in disease
History of Epi: Hippocrates
1st to recognize environment’s role in disease etiology. He listed environmental, dietary, behavior and constitutional conditions.
Recognized early epidemicsWrote thorough descriptions of clinical diseases like tetanus, typhus, and tuberculosis
History of Epi: The demographic approach: Use of vital statistics
14th and 15th century: Italy began tracking death rates and causes (especially from bubonic plague).
1592: England begins to issue death certificates
Incidence
The occuraence, rate, or frequency of a disease, crime or somethign else undesireable
Jakob Henle
1809-1885. Helped create germ theory. Proposed in 1840 that sick people pass contagious substances to healthy individuals
James Lind
1747: studied etiology and treatment of scurvy by assigning random treatment to sailors
John Graunt
1620-1674: “founder of vital statistics”. 1st use of populaiton mortality data to study disease occurance
John Snow
1813-1858: determined that cholera was a water-born infection and conducted extensive studies of household water supply and disease. -Broad Street Pump
Louis Pastuer
1822-1895: Helped create germ theory. isolated bacteria and developed process of killing germs by boiling
Miasma Theory of Disease
1820’s and 1830’s: Prevailing theory of epidemics at the time. Belived that diseases were cause by foul smelling air. Thought epidemics spotaneously generated and were related to poor sanitation and environmental conditions
Morbidity
The incidence of disease. The rate people get sick
Mortality
Death
Mortality Rate
Measure of the number of deaths in a population
Percival Pott
1775: identified chimney soot as cause of scrotal cancer in chimney sweeps
Pierre Charles- Alexandre Louis
1836: “founder of clinical statistics”. Used stats to campaign against blood-letting as a clinical treatment
Prevalence
The number of cases of a given disease or other attribute (e.g. drug use, obesity) that exists in a defined population at a specified time.
Proportionate Mortality Rate (PMR)
deaths from a specific disease / # of deaths = % of deaths in a population caused by a specific disease
The proportion of deaths due to the disease of interest in the exposed population divided by the proportion of deaths due to the disease of interest in the unexposed or reference population
Research
The process of systematically and carefully investigating a single well-defined subject to learn/discover new info about the world
Research Steps
- Identify study question
- Select study approach
- Design study and collect data
- Analyze data
- Report findings
Robert Koch
1843-1910: Helped support germ theory. Used microscopes to see the microbes that cause tuberculosis (1882) and cholera (1883). Worked on immunization for a range of diseases including anthrax. One of the father of vaccines.
Sharp rivalry with Pasteur
Validity
The degree to which results of a study are likely to be true, beliveable and free of bias
What is Epidemiology
“The study of distribution and determinants of health related states in human populations
“epi=”upon” + demos=”people” + logia= “the study of”
The basic science of public health that provides a framework for identifying public health problems, causes and solutions
William Farr
1807-1883: 40 years as chief of vital statistics in England. Established national registration system.
Year Royal Society of London begins publishing life tables
1662
(Crude) Mortality Rate (CMR)
deaths from all causes (or a specific cause) / # of persons in the total population
– Units are usually reported “per # of people” (like /1000 or /10,000)
– Example: Normalville had an annual death rate of 30/1000 in 2010, which means that if the town has a total population of 5000 people, 150 died that year
Comparing Rates
- Ratio: a/b, where a is the numerator and b is the denominator
- Proportion: a ratio with the numerator (a) included in the denominator (b); ranges from 0 to 1 (or 0% to 100%, if converted to a percentage by multiplying by 100)
- Rate: Δx/Δy, a measure of change in one quantity per unit change in another quantity (like a change in the number of people alive (Δ x) per change in time over one year (Δ y))
- Risk: a conditional probability of disease occurrence for an individual
RR
RR = Rate Ratio = Risk Ratio = Relative Risk = Relative Rate – These terms are generally used as synonyms even though rate and risk should be distinct concepts
• RR = (rate in population 1)/(rate in population 2) where population 2 is the “reference population”
– The two populations must be independent (no members in common)
• When using proportions and rates for description and comparisons of populations:
– Define the units carefully
– Use the same units across comparisons
Incidence
The number of NEW cases of a disease occurring in a time period / Total population at risk in that time period
– “at risk” = susceptible = does not already have the disease
Prevalence
The number of EXISTING cases of a disease at a specified time / Total population at the specified time
Incidence helps track
- New cases
- Measures changes in disease occurrence
- Often used in infectious / acute disease studies
- Used for investigating the causes of disease (etiology)
Prevalence helps track
- Existing cases
- Measures how much disease is in the population
- Often used in chronic disease studies
- Used for description and planning health care needs
Pandemic
Global Epidemic
Prevalence is increased by…
- Longer duration of the disease
- Prolongation of life of patients without cure
- Increase in new cases (incidence)
- Out-migration of healthy people
- In-migration of cases
- Improved diagnostic facilities (better reporting)
Prevalence is decreased by…
- Shorter duration of disease
- High case-fatality rate from disease
- Decrease in new cases (incidence)
- In-migration of healthy people
- Out-migration of cases
- Improving cure rates of disease
Point Prevalence
the prevalence of a disease in a population at a single point in time
Period Prevalence
the prevalence of a disease in a population over a specified period of time (includes cases at the start of the period and any subsequent new cases)
• Period Prevalence = Point Prevalence + Incidence
Population Dynamics (3 types)
- Fixed Population: a group of persons, all of whom are available for follow-up starting at the same time (may have different lengths of follow-up, but no new entries)
- Dynamic Population: a group of persons, all of whom are available for follow-up, but starting at different times and for different lengths of follow-up
- Steady-State Population: a dynamic population in which the number of persons entering the population is equal to the number of persons leaving
Fixed Population
a group of persons, all of whom are available for follow-up, starting at the same time
(may have different lengths of follow-up, but no new entries)
Dynamic Population
a group of persons, all of whom are available for follow-up, but starting at different times and for different lengths of follow-up
Steady-State Population
a dynamic population in which the number of persons entering the population is equal to the number of persons leaving
Person-Years
- Allows for measurement of long-term disease processes in dynamic populations (accounts for persons who move to/from a population, are born/die, develop disease, drop out of a study, etc.)
- Incidence can be reported in terms of person-years:“The incidence of the disease was 12.6 per 1000 person-years in our study population.”
- This could represent 100 people followed for 10 years each OR 1000 people followed for 1 year each OR many people followed for various lengths of time
Burden of Disease (BOD) Estimates (population level) (3 types)
- YLL: Years of Life Lost to premature death– An estimate of mortality that represents the significance of a disease in a population, with greater weight given to diseases that affect younger persons. Based on rough assumptions about how long people “should” live in a given population; an estimate rather than a calculation.
- YLD: Years of Life lived with Disability
- DALYs: Disability-Adjusted Life Years (years lost to premature death or to disability)– An estimate of morbidity that accounts for the burden of disease due to specific causes (including non-fatal injuries and mental disease) in a population.– In a population, DALYs = YLLs + YLDs
YLL
Years of Life Lost to premature death– An estimate of mortality that represents the significance of a disease in a population, with greater weight given to diseases that affect younger persons. Based on rough assumptions about how long people “should” live in a given population; an estimate rather than a calculation.
YLD
Years of Life lived with Disability
DALYs
Disability-Adjusted Life Years (years lost to premature death or to disability)– An estimate of morbidity that accounts for the burden of disease due to specific causes (including non-fatal injuries and mental disease) in a population.– In a population, DALYs = YLLs + YLDs
