1. INTRODUCTION TO EPIDEMIOLOGY FIFTH EDITION
© 2010 Jones and Bartlett Publishers, LLC
INTRODUCTION TO
EPIDEMIOLOGY
FIFTH EDITION

2. FOUNDATIONS OF EPIDEMIOLOGY
© 2010 Jones and Bartlett Publishers, LLC
Chapter 1:
FOUNDATIONS OF EPIDEMIOLOGY

3. So you’ve told your friends “I’m taking epidemiology this semester”:
And they’ve said:
“You're studying what? But why…..?”
“That has something to do with skin diseases, right?”
“Ok, so what else are you studying?”

4. Defining epidemiology
The word epidemiology is based on the Greek words
epi—prefix meaning on, upon, or befall;
demos—root meaning the people; and
logos—suffix meaning the study
In other words, epidemiology is the study of what befalls the population
© 2010 Jones and Bartlett Publishers, LLC

5. What is epidemiology?
“The study of the distribution and determinants of health related states and events in populations, and the application of this study to control health problems”
John M. Last, Dictionary of Epidemiology

6. Key terms in the definition
Study - Epidemiology involves sound methods of scientific investigation.
Methods rely on careful observation and the use of valid comparison groups to determine whether the observed health events differ from what might be expected
© 2010 Jones and Bartlett Publishers, LLC

7. Key terms in the definition
Distribution
Study of frequency and pattern of health events in the population
Frequency – number, and number in relation to the population
Pattern – the health-related state or event by person, place, and time characteristics
© 2010 Jones and Bartlett Publishers, LLC

8. Key terms in the definition
Determinants
Search for causes and other factors of health-related states or events
© 2010 Jones and Bartlett Publishers, LLC

9. Key terms in the definition
Health-related states or events
Disease states
cholera, influenza, pneumonia, mental illness
Conditions associated with health
physical activity, nutrition, environmental poisoning, seat belt use, and provision and use of health services
Events
injury, drug abuse, and suicide
© 2010 Jones and Bartlett Publishers, LLC

10. Key terms in the definition
And the final phrase:
“to control health problems”.
© 2010 Jones and Bartlett Publishers, LLC

11. What is epidemiology, really?
Basic science of public health
What causes disease?
How does disease spread?
What prevents disease?
What works in controlling disease?

12. So why is epidemiology a big deal?
It provides the scientific evidence we need to prevent disease and injury and to promote health.
It helps in the prioritization of research
It helps identify individuals within a population who are at greatest risk and allows us to target interventions.
It helps us evaluate the effectiveness of programs in improving the health of the population.
(continues on next slide)

13. Continued…
It helps in the understanding of the natural history of disease from precursor states through clinical course
It helps in the surveillance of disease and injury occurrence in populations
It helps in the investigation of disease outbreaks
– Milton Terris, The Society for Epidemiologic Research (SER) and the future of epidemiology. Am J Epidemiol 1992; 136(8): , p 912

14. Epidemic, endemic, and pandemic
Epidemic – Health-related state or event in a defined population above the expected over a given period of time
Endemic – Persistent, usual, expected health-related state or event in a defined population over a given period of time
Pandemic – Epidemic affecting a large number of people, many countries, continents, or regions
© 2010 Jones and Bartlett Publishers, LLC

15. Let’s go back in history: The Plaque (Black Death)
Place and time: Europe in the Middle Ages
The causative pathogen: Yersinia pestis, a bacterium
The source: Fleas that infest black rats
Transmission: Via the skin through the bite of the flea or through the handling of infected animals
OR through the inhalation of aerosolized droplets from individuals
Cure: Readily treatable with antibiotics
The problem: When treatment is delayed, the bacteria produces a pneumonia that progresses very rapidly – and that can spread from person-to-person.

16. The pathogen

17. The culprit

18. The infection: Lymph node phase

19. Pneumonic phase

20. The outcome

21. July 2012 59 year old male from Prineville, Oregon

22. Now fast forward from the Middle Ages:
Time and place: September 30, 1993 in
Maharashtra State, in India
Event: Earthquake levels over one million homes.
Result: Local farmers harvest and store their crops, then leave the area
Problem: August 1994, farmers return to the region and the stored grains (which have now been inhabited by rats fleas Yersinia pestis.

23. Then things start rolling…
September 14, 1994 – four cases of bubonic plague in Mamala, Beed District, Maharashtra State.
Health care infrastructure still not equipped to handle disease surveillance and control following earthquake
September 18, 1994 Time for the Festival of Ganesh in Surat, a crowded city 100 miles northwest of Mamala

24. And things snowball…
September 21, 1994 cases of pneumonic plague are reported in Surat
Public hospital doctors alert private doctors, but 80% flee Surat - private clinics and hospitals are closed
September 22, 1994 – media converge in India describing the “Surat Fever”.
500,000 Surati’s leave the region within one week

25. It gets worse…
Suratis then board trains traveling to destinations throughout India and reside in numerous densely-populated cities.
Five Indian states then declare an emergency health alert
Actions are slowly taken by the Indian federal government and for the most part, are ineffectual
Minister of Health is not even a physician.
World Health Organization is also ineffectual.

26. The result… Medical personnel who remained in Surat are now exhausted
Sales of tetracycline soar, supplies become become depleted.
Limited expertise in the Plague (CDC at the time only has one part-time scientist with knowledge in this area).

27. The disaster escalates…
Indian and multinational drug companies promote antibiotics, cleansers, pesticides, rat poison to battle the disease
20% of the tourism packages scheduled at the time are canceled
Gulf State Nations, Pakistan, and Sri Lanka ban all flights, citizens, goods, and postal communications with the other sectors of India.
Bombay stock market crashes

28. Other countries now react….
Russia, China, Egypt, Malaysia, Bangladesh terminate all connections to India
Others countries inspect all travelers arriving from India (10 suspected cases in NYC had malaria, typhoid, viruses, liver dis.)
The airline KLM sprays pesticides in plane cabins.
Delhi closes all public schools.
October 2, 1994 – Indian officials report over 4,000 cases of the Plague

29. Two major research organizations in India engage in “stand-off” over specimens and decline outside laboratory assistance (despite the lack of adequate lab equipment and air- conditioning.
By this point, most of the initial specimens have deteriorated through lack of proper handling.

30. As a result…. Lack of definitive laboratory diagnosis
Alternative theories abound – hantavirus, melioidosis, Burkholderia pseudomallei, leptospirosis, tularemia, Pseudomonas pseudomallei, conspiracy theories (rebels, U.S.).
Finally, the Ministry of Defense takes over all remaining blood and sputum samples.

31. And in the end….
Thousands of those who are worried (but are not ill) begin to occupy the hospitals.
Widespread inappropriate use of antibiotics, DDT.
$1.3 billion lost trade and tourism.
The actual death cases in Surat were 56.
From late August to mid October 1994, a total of 693 suspected plague cases, out of which 488 were from Maharashtra, were reported by India to World Health Organization.
In Maharashtra, with the exception of Surat, the reported cases were mostly bubonic plague

32. Bottom line:
Epidemiology helps us prevent this type of catastrophic event from occurring in the future.
What might have been done differently in the Plague scenario?

33. How? By first using descriptive epidemiology
Answering the who, what, when, and where questions is prerequisite to effective education, screening, prevention, and control programs
© 2010 Jones and Bartlett Publishers, LLC

34. Analytic epidemiology
Analytic epidemiology involves identifying and quantifying associations, testing hypotheses, and identifying causes of health-related states or events
Explains why and how health-related states or events occur
Ex. Cigarette smoking associated with lung cancer
© 2010 Jones and Bartlett Publishers, LLC

35. Common source, propagated, and mixed epidemics
Point
Intermittent
Continuous
Propagated
Spread from person-to-person
Mixed epidemics
A mixture of common source and mixed
© 2010 Jones and Bartlett Publishers, LLC

36. Propagated
Arise from infections being transmitted from one infected person to another
Transmission can be through direct or indirect routes
Host-to-host epidemics rise and fall more slowly than common source epidemics
© 2010 Jones and Bartlett Publishers, LLC

37. Mixed epidemics
Occurs when a common source epidemic is followed by person-to-person contact and the disease is spread as a propagated outbreak
Example – Shigellosis occurred among a group of 3000 women attending a music festival. Over the next few weeks, subsequent generations of shigella cases spread by person-to-person transmission from festival attendees.
© 2010 Jones and Bartlett Publishers, LLC

38. Disease transmission Disease transmission usually occurs by
direct, person-to-person contact (e.g., STDs)
fomite-borne (e.g., Hepatitis A spread by a contaminated eating utensil)
vehicle-borne (e.g., HIV/AIDS spread through needle sharing drug users)
vector-borne transmission (e.g., Malaria spread through mosquitoes)
Which one applies to the Plague scenario?
© 2010 Jones and Bartlett Publishers, LLC

39. Accurate assessment requires a standard case definition
A standard set of criteria, or case definition, assures that cases are consistently diagnosed, regardless of where or when they were identified and who diagnosed the case
© 2010 Jones and Bartlett Publishers, LLC

40. Primary case, index case
A case is a person who has been diagnosed as having a disease, disorder, injury, or condition
The first disease case in the population is the primary case.
The first disease case brought to the attention of the epidemiologist is the index case.
The index case is not always the primary case.
© 2010 Jones and Bartlett Publishers, LLC

41. Secondary case
Those persons who become infected and ill after a disease has been introduced into a population and who become infected from contact with the primary case
© 2010 Jones and Bartlett Publishers, LLC

42. The epidemiology triangle for infectious disease

43. Triangle is based on the communicable disease model
Shows the interaction and interdependence of agent, host, environment, and time as used in the investigation of diseases and epidemics.
Agent is the cause of the disease
Host is an organism, usually a human or an animal, that harbors a disease
Environment includes those surroundings and conditions external to the human or animal that cause or allow disease transmission
Time accounts for incubation periods, life expectancy of the host or the pathogen, and duration of the course of the illness or condition.
© 2010 Jones and Bartlett Publishers, LLC

44. Stopping an epidemic
An epidemic can be stopped when one of the elements of the triangle is interfered with, altered, changed, or removed from existence, so that the disease no longer continues along its mode of transmission and routes of infection
© 2010 Jones and Bartlett Publishers, LLC

45. The chain of infection
There is a close association between the triangle of epidemiology and the chain of infection
© 2010 Jones and Bartlett Publishers, LLC

46. The three levels of prevention used in public health and epidemiology
Primary prevention (occurs prior to exposure)
Immunization
Sanitation
Education
Media campaigns
Warning labels
© 2010 Jones and Bartlett Publishers, LLC

47. Active primary prevention
Requires behavior change on part of subject
Wearing protective devises
Health promotion
Lifestyle changes
Community health education
Ensuring healthy conditions at home, school and workplace
© 2010 Jones and Bartlett Publishers, LLC

48. Passive primary prevention
Does not require behavior change
Vitamin fortified foods
Fluoridation of public water supplies
© 2010 Jones and Bartlett Publishers, LLC

49. Secondary prevention Occurs to reduce the progress of disease
The disease already exists in the person
Cancer screening – cancer already present. The goal is to detect the cancer before clinical symptoms arise in order to improve prognosis and prevent conditions from progressing and from spreading
© 2010 Jones and Bartlett Publishers, LLC

50. Tertiary prevention
To reduce the limitation of disability from disease
The disease has already occurred
Physical therapy for stoke victims
Halfway houses for recovering alcoholics
Shelter homes for the developmentally disabled
Fitness programs for heart attack patients
© 2010 Jones and Bartlett Publishers, LLC

51. Any questions?