epi

• study of distribution and determinants of health related states or events in specific populations and the application of this study to control health problems
• • Goal, essentially, is to limit undesirable health events in a community

• Epidemic:
• an unexpectedly large number of cases of an illness, specific health-related behavior, or other health related event in a particular population at a particular time and place

• Endemic disease:
• disease that occurs regularly in a population

• Epidemiologist
• : studies disease occurrence in defined populations

• Pandemic: outbreak of a disease over a wide geographical area, such as a continent
• • Example: avian influenza, which the books list as being the next possible agent to reach pandemic proportions.

• History of Epidemiology: 300 B.C., late 1600’s, 1849:
• : Hippocrates suggests link between disease and environment
• •Regression until late 1600’s; return to spiritual-causation belief
• •1849: John Snow studies epidemiology of cholera and extinguishes London outbreak, thereby limiting death and preserving health

births / total population

number of sick / total population at risk

• number deaths / total population at risk
• Based on population risk: those who are susceptible to a disease in a given population

number of new health related cases of a disease / total number in population at risk

• •Number of events
• •Number of cases: the number of people who are sick
• •Number of deaths

lasts less than 3 months

lasts longer than 3 months

• incidence rate calculated for a specific population for a single disease outbreak expressed as a percentage
• oEx: number of people on a flight become sick, and it is suspected that the flight caused the illness. Attack rate could be calculated for the passengers to express who became ill.

• all current cases / total population
• oUseful for chronic diseases: know how many are suffering

denominator includes total population

• # births in a year / mid year population
• +: easy to obtain, good for comparing populations
• -: misleading if populations differ in age/attributes

rate used to make comparisons between groups over time when groups differ in age structures

measures morbidity or mortality for particular populations or diseases

• death rate due to a particular disease
• Number of deaths by disease / total population

• percentage of cases of a disease that result in death
• # deaths in specified time / number of cases in same period

• percentage of overall mortality in a population that is attributable to particular cause
• # deaths due to specific disease / total number of deaths from all causes in same population in the same period of time

• • sometimes only 35% of cases with diseases are reported
• • clinics may be too busy to report every case
• • patients can recover before treatment and may not seek care
• • reporting depends on disease severity

mortality statistics

• what death would be if no changes occurred in the age makeup of a population
• o they are a better indicator for examining changes in risk of death over a period of time

• average number of years a person from a specific cohort is projected to live from a given point of time
• • has generally increased in America

• -Years of potential life lost (YPLL):
• subtracting a person’s age at death from a predefined, standard age
• •age 75 often used as the standard
• operson dies at 59. 75-59 = 16 years
• vary depending on cause
• Accidents, cancer kill younger so higher YPLL

• -Disability adjusted Life years:
• measure for the burden of disease that takes into account premature death and loss of healthy life resulting from disability
• •mortality does not express burden of disease
• Ex: polio causes loss of healthy life but not reflected in death tables

sometimes referred to has healthy life expectancy, number of years of healthy life expected, on average, in a given population

• •data: income, employment, family size, education, dwelling type, and many other social indicators
• •used for calculating disease and death rates for program planning

• statistical summaries of vital records; records major life events
• •births, deaths, marriages, divorces
• birth: maternal and prenatal care, delivery
• deaths: rates, expectancy, leading causes, infant mortality

• Morbidity and Mortality Weekly Report
• -reported diseases are shown weekly

• •health interviews of people
• •clinical tests
• •survey of places where care is received

• •health/nutritional of the general US Population
• •based on PE, clinical and lab tests, and related procedures
• o most authoritative source of clinical info on American people

state-based telephone survey to ascertain prevalence of high risk behavior, like smoking or drinking

• -Youth Risk Behavior Survey (YRBS): six categories of risks in youth
• •behaviors that contribute to unintentional violence and injuries
• •tobacco use
• •alcohol and drug use
• •STIS and pregnancy
• •HIV
• •Unhealthy dietary habits and physical inactivity

• -National Health Care Survey (NHCS):
• nine different national surveys that gather info on nation’s healthcare system

• describes disease with respect to person, place, and time (the extent, essentially)
• First studies carried out on diseases!! Valuable info on detection patterns.
• Who: head count, as well as age, sex, race, marital status, etc.
• When: categorized by time of occurrence
• Summarized by year, for example

graphic display of disease where each case can be traced to a single source of exposure Used to calculate incubation period

time between exposure and onset of symptoms

exposure occurs at a single point in time

• exposure is intermittent
• Need to discover these to prevent future exposure

• Primary cases appear at one end, secondary cases after primary, and tertiary further along the graph
• Where: residential addresses, travel history are recorded
• Restaurants, shopping, etc.
• •Limitations of descriptive studies: not applicable to outbreaks elsewhere and cannot provide info on disease trends.

• -Analytic studies:
• test hypotheses about relationships between health problems and possible risk factors

• • increase probability of disease
• o Ex. Does smoking increase risk of lung cancer?
• • Two different types of analytic studies exist:

• investigates natural course of disease
• Observational studies can be divided into:

info about exposure and disease are collected at the same time

• seeks to compare diagnosed with a disease and those who are not for prior exposure to specific risks
• • Familial, behavioral links
• • Don’t prove causation alone, but indicate future direction of question

• cohort is classified by exposure to one or more risk factors and observed to determine the rates at which the disease develops in each class
• Can be prospective (observing a group to see if cigarette smoking leads to disease) or retrospectively (exposure and outcome has already happened)

o rate of development of a disease, as the patients already have it

probability about association between risk factors and developing a disease

calculate incidence rate

statement of relationship between risk factor and disease (more definitive)

expensive, not practical for rare cases, and take many years to complete

• carried out to identify cause of a disease or determine effectiveness of an intervention
• Use of control and experimental groups, placebo, etc.

assigning subjects to treatments in a non-organized manner

subject remain uninformed and unaware of groups