Chapter 2Chapter 2

Epidemiological Data Sources Epidemiological Data Sources and Measurementsand Measurements

Epidemiology & BiostatisticsEpidemiology & BiostatisticsCopyright Kaplan University 2009Copyright Kaplan University 2009

Types of Data Used in Health Types of Data Used in Health StudiesStudies

►Denominator DataDenominator Data A definition of the population at riskA definition of the population at risk

►Example: Smokers at risk for lung cancerExample: Smokers at risk for lung cancer►Example: Men over the age of 40 who are in Example: Men over the age of 40 who are in

excess of 50 pounds or more over their ideal excess of 50 pounds or more over their ideal weight at risk of coronary artery disease.weight at risk of coronary artery disease.

►Women aged 70 and over who are calcium Women aged 70 and over who are calcium deficient and at risk of developing deficient and at risk of developing osteoporosisosteoporosis

ContinuedContinued

►Numerator DataNumerator Data A definition of the events or conditions of A definition of the events or conditions of

concernconcern►Example: Lung CancerExample: Lung Cancer►Example: Coronary Artery DiseaseExample: Coronary Artery Disease►Example: Osteoporosis/Broken hipsExample: Osteoporosis/Broken hips

Methods of Data CollectionMethods of Data Collection

►United States CensusUnited States Census Takes place every 10 yearsTakes place every 10 years Also collects continuously data on births Also collects continuously data on births

and deaths through the Dept. of Vital and deaths through the Dept. of Vital StatisticsStatistics

http://www.lpoy.org/databook/1992-99%20Teenage%20Vital%20Statistics-Virginia_files/image007.gif

The U.S. CensusThe U.S. Census

►A method of data collection used by A method of data collection used by the federal governmentthe federal government

►Completed every ten years in a year Completed every ten years in a year that ends with “0”that ends with “0”

►Next census collection will be in 2010Next census collection will be in 2010►Last census collection was in 2000Last census collection was in 2000

U.S. Vital StatisticsU.S. Vital Statistics

►Basically deals in birth and death of Basically deals in birth and death of the populationthe population

►Local and state officials collect Local and state officials collect informationinformation

►Federal government collates the Federal government collates the information after it is collectedinformation after it is collected

Cause of DeathCause of Death

►ImmediateImmediate What event What event

precipitated precipitated the actual the actual deathdeath

►UnderlyingUnderlying Any event that Any event that

the immediate the immediate cause of death cause of death was a symptom was a symptom ofof

ExampleExample

History: Child is admitted to hospital History: Child is admitted to hospital after being struck by car. He is after being struck by car. He is unresponsive and shows signs of blunt unresponsive and shows signs of blunt trauma to thoracic (chest) area. trauma to thoracic (chest) area. During ER triage and examination he During ER triage and examination he begins to hemorrhage as a result of a begins to hemorrhage as a result of a aortic tear and subsequently dies. aortic tear and subsequently dies.

CAUSES?CAUSES?

CAUSESCAUSES

► ImmediateImmediate Aortic TearAortic Tear

► (bleeds to death due (bleeds to death due to a ruptured aorta)to a ruptured aorta)

► UnderlyingUnderlying Car accident caused Car accident caused

blunt traumablunt trauma

► (the car striking the (the car striking the child caused a blunt child caused a blunt trauma which in turn trauma which in turn tore the aorta)tore the aorta)

Refer to Text Pp. 22Refer to Text Pp. 22Table 2-1Table 2-1

What do you think?What do you think?

►If someone dies of one of If someone dies of one of these diseases, is the disease these diseases, is the disease the underlying or the the underlying or the immediate cause of death?immediate cause of death?

Let’s discussLet’s discuss

EPIDEMIOLOGICAL REGISTRIESEPIDEMIOLOGICAL REGISTRIES

►Disease RegistriesDisease Registries State disease specific registriesState disease specific registries

►Data from Third Party PayersData from Third Party Payers Veterans Administration, etc.Veterans Administration, etc.

►Novel RegistriesNovel Registries Australian Rheumatoid Arthritis DatabaseAustralian Rheumatoid Arthritis Database

Epidemiological Epidemiological MeasurementsMeasurements

►Frequency – deals with numbersFrequency – deals with numbers Incidence – number of occurrences (well: Incidence – number of occurrences (well:

ill or live: dead)ill or live: dead) Prevalence – number of cases within a Prevalence – number of cases within a

population at a given timepopulation at a given time

►Risk – deals with proportion of people Risk – deals with proportion of people unaffected at the beginning of a studyunaffected at the beginning of a study

ContinuedContinued

►Rates: Frequency of events that occur Rates: Frequency of events that occur in/during a defined period of time.in/during a defined period of time. Generally the following rules are in playGenerally the following rules are in play

►Decimal fractions are avoided as they are Decimal fractions are avoided as they are awkward in discussion (i.e. 1/100awkward in discussion (i.e. 1/100thth of a death?) of a death?)

►Numerator: rate of the frequencyNumerator: rate of the frequency►Denominator: number of people at risk during Denominator: number of people at risk during

period being studied/consideredperiod being studied/considered►Constant multiplier: usually 100 in order to get Constant multiplier: usually 100 in order to get

a percentage; 1000, 10,000 or 100,000 used a percentage; 1000, 10,000 or 100,000 used for numbers less than “1”. Not used a lot.for numbers less than “1”. Not used a lot.

Risk Versus RateRisk Versus Rate

► Risk denominator does Risk denominator does not changenot change

► Risk is the event itself, Risk is the event itself, i.e. death, illness, etc.i.e. death, illness, etc.

► Risks are estimated by Risks are estimated by ratesrates

► Rates denominator Rates denominator constantly changesconstantly changes

► Rate is the # of times Rate is the # of times an event happensan event happens

► Rate estimates risk Rate estimates risk when:when: Event occurs only once Event occurs only once

per individual during the per individual during the studystudy

Proportion of population Proportion of population affected is smallaffected is small

Time interval of event is Time interval of event is shortshort

Types of RatesTypes of Rates

► Incidence RateIncidence Rate►Prevalence RatePrevalence Rate

►Crude RatesCrude Rates►Specific RatesSpecific Rates►Death RatesDeath Rates

Maternal and Fetal Associated Maternal and Fetal Associated RatesRates

► Infant mortality rates: death of infants born Infant mortality rates: death of infants born alivealive

► Neonatal and Post-neonatal Mortality Rates: Neonatal and Post-neonatal Mortality Rates: death of infants a) during first 28 days of life death of infants a) during first 28 days of life (neo=new) and b) from 28(neo=new) and b) from 28thth day to 1 year of day to 1 year of life (post=after event).life (post=after event).

► Perinatal mortality rates: deaths that occur Perinatal mortality rates: deaths that occur around the time of birth (i.e. stillborn)around the time of birth (i.e. stillborn)

► Maternal mortality rates: death of a Maternal mortality rates: death of a pregnant woman as a result of pregnancy pregnant woman as a result of pregnancy related health issuerelated health issue

ConclusionConclusion

►Please be sure and re-read this section Please be sure and re-read this section we have covered a lot of ground but we have covered a lot of ground but there is much more within the chapter there is much more within the chapter for you to discover.for you to discover.

►QUESTIONS ???QUESTIONS ???

Chapter 3Chapter 3

Epidemiologic Surveillance & Epidemiologic Surveillance & Outbreak InvestigationOutbreak Investigation

Who is Responsible for US Who is Responsible for US Surveillance?Surveillance?

Types of SurveillanceTypes of Surveillance

► Passive SurveillancePassive Surveillance Routine data Routine data

collectioncollection► PhysiciansPhysicians► ClinicsClinics► LaboratoriesLaboratories► HospitalsHospitals

Example: Infant Example: Infant Mortality rate in Mortality rate in Duval County, Florida Duval County, Florida in January 2008in January 2008

► Active SurveillanceActive Surveillance Periodic reportsPeriodic reports

► By phone or visitBy phone or visit► Labor intensiveLabor intensive► Health departmentsHealth departments

Example: The Example: The insuring that TB insuring that TB patients are taking patients are taking their medications as their medications as directeddirected

Baseline Data SurveillanceBaseline Data Surveillance

►Baseline data is based on information Baseline data is based on information that is considered the norm in terms of that is considered the norm in terms of disease or health issues in a given disease or health issues in a given area at a given time.area at a given time. Example: Cases of influenza that are Example: Cases of influenza that are

reported in Houston County, Georgia reported in Houston County, Georgia during the months of October through during the months of October through April of the last 5 years.April of the last 5 years.

Seasonal Variations of Disease Seasonal Variations of Disease PrevalencePrevalence

►Depends on the route of transmissionDepends on the route of transmission Examples:Examples:

► Mosquitoes spread West Nile Virus in the Mosquitoes spread West Nile Virus in the summer monthssummer months

►Heartworm disease in canines is more likely to Heartworm disease in canines is more likely to occur during the summer months due to occur during the summer months due to prevalence of mosquitoesprevalence of mosquitoes

►Lyme Disease is more likely to be contracted Lyme Disease is more likely to be contracted due to a) high population of due to a) high population of IxodesIxodes ticks and ticks and b) popular time for outdoor activities putting b) popular time for outdoor activities putting people at riskpeople at risk

Years?Years?

► Calendar YearCalendar Year Runs from January 1 Runs from January 1

to December 31to December 31stst

► Epidemiologic YearEpidemiologic Year Runs from the Runs from the

beginning of the beginning of the month of the lowest month of the lowest incidence to the end incidence to the end of the month of the of the month of the highest incidence.highest incidence.

Things to Know About Things to Know About OutbreaksOutbreaks

►Epidemic: Occurrence of disease at an Epidemic: Occurrence of disease at an unusual frequencyunusual frequency

►One must know the normal rates at One must know the normal rates at which diseases occur in order to spot an which diseases occur in order to spot an epidemic epidemic (One cannot recognize the abnormal if you do not know the normal)(One cannot recognize the abnormal if you do not know the normal)

►Syndromic Surveillance: Surveillance Syndromic Surveillance: Surveillance which is looking for unlikely symptoms which is looking for unlikely symptoms that may identify possible bio-terrorist that may identify possible bio-terrorist activity using biologicals.activity using biologicals.

How to Investigate a Suspected How to Investigate a Suspected EpidemicEpidemic

►Understand various types of epidemics:Understand various types of epidemics: Epidemic: the unusual occurrence of Epidemic: the unusual occurrence of

diseasedisease Endemic: disease occurring regularlyEndemic: disease occurring regularly Epizootic: disease outbreak occurring within Epizootic: disease outbreak occurring within

animal populations animal populations Enzootic: disease that is entrenched though Enzootic: disease that is entrenched though

not displaying change within an animal not displaying change within an animal populationpopulation

Elementary my dear Elementary my dear Watson…Watson…

► Investigating an Epidemic:Investigating an Epidemic: Establish a common diagnosis Establish a common diagnosis Establish a case definition (criteria of the Establish a case definition (criteria of the

disease)disease) Establish a given number of diagnosed Establish a given number of diagnosed

casescases►This is somewhat predicated by the number of This is somewhat predicated by the number of

cases of the disease normally seen in the area cases of the disease normally seen in the area at the same time of the yearat the same time of the year

Establish Time, Place and PersonEstablish Time, Place and Person

The HypothesisThe Hypothesis

►The development of a hypothesis The development of a hypothesis should address three things:should address three things: Source of infectionSource of infection Pattern of spreadPattern of spread Mode of transmissionMode of transmission

►Testing of Hypothesis should be done Testing of Hypothesis should be done by:by: Laboratory studiesLaboratory studies Case Control studiesCase Control studies

HISTORY HISTORY

A family spending the summer on a resort island, hires a A family spending the summer on a resort island, hires a cook and gardener to take with them for a total of eleven cook and gardener to take with them for a total of eleven people. Shortly after arriving six of the eleven people fall ill people. Shortly after arriving six of the eleven people fall ill with diagnosed Typhoid Fever. Soon after the outbreaks of with diagnosed Typhoid Fever. Soon after the outbreaks of Typhoid, the cook left for fear of her own life. Soon after Typhoid, the cook left for fear of her own life. Soon after with treatment, rest, good food and the pleasant tropical with treatment, rest, good food and the pleasant tropical surroundings, the family began to recover from the illness. surroundings, the family began to recover from the illness. It was later discovered that the recently departed cook had It was later discovered that the recently departed cook had worked for seven different families. During the course of worked for seven different families. During the course of her employment, 22 people were struck down with Typhoid her employment, 22 people were struck down with Typhoid Fever. Fever.

? ? ?? ? ?

►What was the source of the infection?What was the source of the infection?

►What was the pattern of spread?What was the pattern of spread?

►What was the mode of transmission?What was the mode of transmission?

AnswersAnswers

►Source of Infection: The cookSource of Infection: The cook►Pattern of Spread: Contaminated food Pattern of Spread: Contaminated food ►Mode of Transmission: Oral IngestionMode of Transmission: Oral Ingestion

TYPHOID MARYTYPHOID MARY

Hypothesis Proved…Now Hypothesis Proved…Now What?What?

► Initiate control measures through Initiate control measures through interventionintervention SanitationSanitation ProphylaxisProphylaxis DiagnosisDiagnosis TreatmentTreatment Control/eradication of vectorsControl/eradication of vectors

►Follow Up SurveillanceFollow Up Surveillance

Questions ?Questions ?