1. The study of the trends and patterns of diseases Key Points
Epidemiology
The study of the trends and patterns of diseases
Key Points

2. Why Do We Use Epidemiology
To identify diseases
To identify outbreaks
To find the sources of illnesses
To identify risk factors for diseases
To identify interventions that change the risk for or course of a disease

3. But What is Epidemiology?
Epidemiology is the study of how often different diseases occur within or between populations and also seeks to uncover why?
The epidemiology of a disease is frequently an integral part of it’s basic description

4. A bit of history
Hippocrates ( B.C.) wrote a work called “epidemics” – in which he meticulously described the symptoms and course of diseases and related them to the seasons, geography and the type of people who became ill
The term epidemiology has shared origins with the word epidemic
Epidemics caused by bacterial pathogens form the basis on which epidemiology is based – these techniques can now be applied to non-infectious diseases
Thomas Sydenham (17th cent) is regarded as the “father of epidemiology” due to his careful descriptions of a number of diseases including dysentery, syphilis and TB
The 19th Century was the “golden age of microbiology” and also saw the evolution of statistics
John Snow catalogued the first epidemic of cholera in London (1849) – in many ways he may be regarded as the “founder of modern epidemiology)
In the 1920s the concepts of epidemiology were expanded to non-infectious diseases, particularly diet-related conditions such as pellagra (niacin), scurvy and rickets.

5. Characterising Epidemics
Think simply first – that’s how epidemiology developed as a discipline
Define the population
Define the what constitutes a case
Then get the appropriate data
Analyse the data using the correct methods to answer the questions you want answered
If it is a “new” diseases try to identify it, for “old” diseases seek confirmation

6. Characterising Epidemics
THINK SIMPLY FIRST
Who gets ill? – young, old, male, female, ethnicity, religion, immunocompromised..
Do they have a common occupation or pastime?
Do they have an “event” in common?
Do they live/work/study in proximity to each other?

7. What is a case?
How do you decide if a person has an infectious disease? – what level of evidence or proof do you need?
For “established” diseases there are now fairly clear definitions of a case
But what happens if there is not a known cause – how then do you define a case

8. The Concept of a Population
All epidemiological findings must be related to a defined population
That population can be defined in many ways: geographically, by occupation, by age, by gender, by race, by immune status, etc… almost anything but it must be defined
The results of findings for one defined population can then be compared to those of another defined population if appropriate

9. Data Collection Abstracting information from already available sources
Surveys
Physical examination, clinical studies, screening programmes
Disease surveillance programmes – extensively used in the UK, Europe and the USA for infectious diseases

10. Determining the Risks Of Diseases
This can be very difficult as many diseases are multi-factorial in nature
Diabetes, Heart Disease
The risks factors themselves may be very hard to observe
Genetic markers
Risk factors may interact with each other
Smoking, obesity, lack of activity

11. Modifying Behaviour to Reduce Risks
Once a risk factor has clearly been established, then steps can be taken to reduce the risk
Education is the key, but experience suggests that getting individuals to modify their behaviour (and to maintain the change) is very difficult
STD campaigns work for a time and then people forget the risk
Smoking!!!
Consequently legislation has been introduced that places demands on industry to reduce risks where it can
The food industry is highly regulated to prevent pathogens getting to you

12. Suggested Further Reading
“Epidemiology for the uninitiated” – by Coggon, Rose and Barker – published by the BMJ publishing group – Fourth edition was published in 1997.
This is a short an concise text covering a range of aspects related to epidemiology. It is easy to read and won’t take longer than a couple of hours.