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Chapter 2 Epidemiological Data Sources and Measurements

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1 Chapter 2 Epidemiological Data Sources and Measurements
Epidemiology & Biostatistics

2 Types of Data Used in Health Studies
Denominator Data A definition of the population at risk Example: Smokers at risk for lung cancer Example: Men over the age of 40 who are in excess of 50 pounds or more over their ideal weight at risk of coronary artery disease. Women aged 70 and over who are calcium deficient and at risk of developing osteoporosis

3 Continued Numerator Data
A definition of the events or conditions of concern Example: Lung Cancer Example: Coronary Artery Disease Example: Osteoporosis/Broken hips

4 Methods of Data Collection
United States Census Takes place every 10 years Also collects continuously data on births and deaths through the Dept. of Vital Statistics


6 The U.S. Census A method of data collection used by the federal government Completed every ten years in a year that ends with “0” Next census collection will be in 2010 Last census collection was in 2000

7 U.S. Vital Statistics Basically deals in birth and death of the population Local and state officials collect information Federal government collates the information after it is collected

8 Cause of Death Immediate What event precipitated the actual death
Underlying Any event that the immediate cause of death was a symptom of

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


11 CAUSES Immediate Underlying Aortic Tear
(bleeds to death due to a ruptured aorta) Underlying Car accident caused blunt trauma (the car striking the child caused a blunt trauma which in turn tore the aorta)

12 Refer to Text Pp. 22 Table 2-1 What do you think?
If someone dies of one of these diseases, is the disease the underlying or the immediate cause of death? Let’s discuss

Disease Registries State disease specific registries Data from Third Party Payers Veterans Administration, etc. Novel Registries Australian Rheumatoid Arthritis Database

14 Epidemiological Measurements
Frequency – deals with numbers Incidence – number of occurrences (well: ill or live: dead) Prevalence – number of cases within a population at a given time Risk – deals with proportion of people unaffected at the beginning of a study

15 Continued Rates: Frequency of events that occur in/during a defined period of time. Generally the following rules are in play Decimal fractions are avoided as they are awkward in discussion (i.e. 1/100th of a death?) Numerator: rate of the frequency Denominator: number of people at risk during period being studied/considered Constant multiplier: usually 100 in order to get a percentage; 1000, 10,000 or 100,000 used for numbers less than “1”. Not used a lot.

16 Risk Versus Rate Risk denominator does not change
Risk is the event itself, i.e. death, illness, etc. Risks are estimated by rates Rates denominator constantly changes Rate is the # of times an event happens Rate estimates risk when: Event occurs only once per individual during the study Proportion of population affected is small Time interval of event is short

17 Types of Rates Incidence Rate Prevalence Rate Crude Rates
Specific Rates Death Rates

18 Maternal and Fetal Associated Rates
Infant mortality rates: death of infants born alive Neonatal and Post-neonatal Mortality Rates: death of infants a) during first 28 days of life (neo=new) and b) from 28th day to 1 year of life (post=after event). Perinatal mortality rates: deaths that occur around the time of birth (i.e. stillborn) Maternal mortality rates: death of a pregnant woman as a result of pregnancy related health issue

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

20 Epidemiologic Surveillance & Outbreak Investigation
Chapter 3 Epidemiologic Surveillance & Outbreak Investigation

21 Who is Responsible for US Surveillance?

22 Types of Surveillance Passive Surveillance Active Surveillance
Routine data collection Physicians Clinics Laboratories Hospitals Example: Infant Mortality rate in Duval County, Florida in January 2008 Active Surveillance Periodic reports By phone or visit Labor intensive Health departments Example: The insuring that TB patients are taking their medications as directed

23 Baseline Data Surveillance
Baseline data is based on information that is considered the norm in terms of disease or health issues in a given area at a given time. Example: Cases of influenza that are reported in Houston County, Georgia during the months of October through April of the last 5 years.

24 Seasonal Variations of Disease Prevalence
Depends on the route of transmission Examples: Mosquitoes spread West Nile Virus in the summer months Heartworm disease in canines is more likely to occur during the summer months due to prevalence of mosquitoes Lyme Disease is more likely to be contracted due to a) high population of Ixodes ticks and b) popular time for outdoor activities putting people at risk

25 Years? Calendar Year Epidemiologic Year
Runs from January 1 to December 31st Epidemiologic Year Runs from the beginning of the month of the lowest incidence to the end of the month of the highest incidence.

26 Things to Know About Outbreaks
Epidemic: Occurrence of disease at an unusual frequency One must know the normal rates at which diseases occur in order to spot an epidemic (One cannot recognize the abnormal if you do not know the normal) Syndromic Surveillance: Surveillance which is looking for unlikely symptoms that may identify possible bio-terrorist activity using biologicals.

27 How to Investigate a Suspected Epidemic
Understand various types of epidemics: Epidemic: the unusual occurrence of disease Endemic: disease occurring regularly Epizootic: disease outbreak occurring within animal populations Enzootic: disease that is entrenched though not displaying change within an animal population

28 Elementary my dear Watson…
Investigating an Epidemic: Establish a common diagnosis Establish a case definition (criteria of the disease) Establish a given number of diagnosed cases This is somewhat predicated by the number of cases of the disease normally seen in the area at the same time of the year Establish Time, Place and Person

29 The Hypothesis The development of a hypothesis should address three things: Source of infection Pattern of spread Mode of transmission Testing of Hypothesis should be done by: Laboratory studies Case Control studies

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

31 ? ? ? What was the source of the infection?
What was the pattern of spread? What was the mode of transmission?

32 TYPHOID MARY Answers Source of Infection: The cook
Pattern of Spread: Contaminated food Mode of Transmission: Oral Ingestion TYPHOID MARY

33 Hypothesis Proved…Now What?
Initiate control measures through intervention Sanitation Prophylaxis Diagnosis Treatment Control/eradication of vectors Follow Up Surveillance

34 Questions ?

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