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.

10. CAUSES?

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

13. EPIDEMIOLOGICAL REGISTRIES
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 ?