Broad types of epidemiology

Parcours 1 – Clinical Research -
Epidemiology.
Cours n°1
24/02/2015
Pierre-Yves Ancel
RT : Charlotte Lafougère
RT : Charles Lasar
RL : Corentin Delorme
Introduction to epidemiology.
Plan :
Epidemiology
1. Definitions
2. Purposes
3. To solve health problems
4. Example of tobacco
5. Research areas using epidemiology
I. Definitions
1. Key terms
2. Prevention
3. Quiz
II. Broad types of epidemiology
1. Descriptive epidemiology
2. Analytic epidemiology
3. Experimental epidemiology
III. Contagion movie
Mot du RL: C’était le premier cours du prof qui assurera tous les cours du S2. Il souhaite pouvoir
construire des cours en interaction avec les élèves ce qui nécessite une presence aux cours. Au
vu des MCC, il ne peut normalement pas pénaliser les élèves ne venant pas en cours mais pense
valoriser les élèves présents. Nous serons normalement bientôt informé des modalités de
contrôle continu qu’il décidera d’instaurer.
Le prof a dit qu’il nous enverrait toutes les diapos de son cours où sont présentes les definitions
importantes que vous pouvez déja retrouver dans cette ronéo.
Mot du RT
Le cours est une introduction à l’épidémiologie.
Je déconseille d’apprendre bêtement par cœur mais plutôt de comprendre notamment la
différence entre l’épidemiologie descriptive, analytique et expérimentale, les quelques
définitions, les différentes types de prévention (primaire, secondaire tertiaire )
Par ailleurs le professeur a insisté sur l’importance de la présence des élèves en cours, qui sera
prise en compte dans la note finale ( cf le mot du RL.)
Aussi le cours durera 2h au lieu de 3, c’est à dire 14-16h.

I. Epidemiology
1. Definition
It is the study of:
 Distribution of health outcomes and diseases in populations
 Factors that determine health outcomes and diseases (risk factors)
The application of this study to control health:
 Epidemiologists focus their attention at the level of populations rather than individuals
Purposes
 To determine the extent of a disease found in a community: what is the burden of the
disease?
 To identify the etiology or the cause of a disease and the risk factors (for example the
relation between smoking and getting a lung cancer)
 To study the natural history and prognosis of the disease (for example the speed of the
mortality due to the lung cancer)
 To evaluate both existing and new preventive and therapeutic measures and modes of health
care delivery (like screening to find the lung cancer)
 To provide a foundation for developing public policy and regulatory decisions (for example
the risk of diseases linked to a job can lead to the creation of laws to protect the workers.
There is a regulation on a public scale)
2. To solve health problems
 Data collection about health problems
o Information about when the problem occurred, as well as where and who were
affected
 Assessment – inference
o On the basis of the collected data, epidemiologists generate hypotheses about what
might be causing the health problem
 Hypothesis testing
o Implementation of studies to determine if the hypothesis is accurate
 Intervention
o To prevent the condition from spreading further or to promote healthy behaviors
o Recommendations at the population level
3. Example of tobacco
Dans cet exemple il est seulement intéressant de savoir qu’est ce qu’une étude cas-témoin
(« case control study ») et une étude de cohorte (cohort study).
Très schématiquement pour étudier la survenue de cancer du poumon chez les fumeurs :
Étude de cohorte -> On prend deux groupes de personnes.
On fait fumer le groupe A mais pas le groupe B. On regarde la survenue de cancer chez les deux
groupes.

Étude cas temoin -> On prends deux groupes : Un groupe C où tout le monde a le cancer du poumon
et un groupe D sans cancer. Ici on demande qui est fumeur. Si il y a beaucoup de fumeur dans le
groupe C et moins dans le D, on pourra établir un lien.
 1947 UK: Some scientifics observed that the risk of lung cancer was multiplied by 15 over 25
years. They had two hypothesis: polution and tobacco
 1950: Richard Doll et Bradford Hill conducted a study between people who have lung cancer
and people who don’t have lung cancer. They asked about smoking past to see if exposure
has an impact. It was a retrospective study.
->This study is called “a case control study”
 1951: B Hill launched a study among doctors. He measured they’re tobacco consumption in
1951 and followed them up from 1951 to 2001. It was a cohort study.
 1964: death due to lung cancer raised with smoking, multiplied by 13 for smokers, and by 30
for heavy smokers
4. Research areas using epidemiology (à ne pas connaitre )
 Infectious diseases
 Chronic diseases
 Maternal and child health
 Injury and accidents
 Disability
 Environmental
 Occupation
 Nutrition
 Health behaviors
 Surveillance
 Genetics
 Screening
 Treatment effects
II. Definitions
1. Key terms
 Disease: Any deviation or interruption of the normal structure or function of any part, organ
or system of the body that is manifested by a set of symptoms and signs.
Health: Health is a state of complete physical, mental and social well-being and not merely the
absence of disease or infirmity.
 Public health: refers to all organized measures to prevent disease, promote health, and
prolong life among the population as a whole.
 Endemic: disease or condition present among a population at all time
 Epidemic: a disease in excess in a population
 Pandemic: an epidemic that affects several countries or continent
 Cluster: group of cases in a specific time and place that might be more than expected

2. Prevention
 Primary prevention:
o Before the person gets the disease
o May reduce the occurrence of the disease
o Example: vaccination
 Secondary prevention:
o After the disease occurs but before symptoms
o Aims to find and treat the disease early
o Example: detect skin cancer at an early stage
 Tertiary prevention:
o The person has already had the disease and symptoms
o To prevent complications or rehabs
o Examples: dietary advice to manage diabetes, heart stroke
3. Quiz (sur les définitions endemic/pandemic/epidemic)
 Malaria is present in Africa at all times because of the presence of infected mosquitos.
Maleria is endemic in Africa.
 The Ebola virus in parts of Africa is in excess of what is expected for this region. This virus is
an epidemic.
 HIV/AIDS is one of the worst global diseases in history. It is a pandemic.
III. Broad types of epidemiology
1. Descriptive epidemiology
 Refers to:
o The distribution of a disease/risk factors in populations
o Three characteristics we look for in descriptive epidemiology:
 Person: Who is getting the disease? (Characteristics of a person: age,
ethnicity, sex, education, occupation, SES (socio-economic status)...)
 Place: Where does the disease occur? Where are the rates of people sick
higher/lower? (The climate, the geography, the population density, the
economic development...)
 Time: When does the disease occur (changing or stable, short-term changes
(epidemic), seasonal variation (within a calendar year)…)
 Helps to
o Measure the extent
o Evaluate the trends
o Identify next disease
 Useful for allocation resources, planning programs, hypotheses development
 Typical study design: cross-sectional study
 Long term changes graphic:

We notice here:
o First cases 1981 isolated
o Slight race to 1984
o Very sharp increase from 1984 to 1987
o As of 1987, steady, constant, stable
2. Analytic epidemiology
 Aims to study
o Risk factors
o Preventive factors
 What are the underlying causes of diseases?
 By what mechanism do they operate?
 Typical study designs: cohort, case-control
 Three characteristics to study the cause:
o Host factors, like the age, the genetic predisposition, the personal behavior, the
immunologic factors. These factors influence the chances of getting the disease but also
on its severity
o Agents, they can be biological, physical or chemical like nutrients, allergens, radiation,
and microbes... These agents are necessary for the disease to occur
o Environment, which includes external conditions (physical, biological or social). These
factors contribute to the disease process
 Cardiovascular disease:
o Agent: tobacco
o Hosts: family history of CVD (Cardiovascular Disease)
o Environment:
 That supports this (poverty, cultural norms…)
 Social factors influence who smoke or who doesn’t
3. Experimental Epidemiology
 Evaluating the effectiveness of preventive or therapeutic interventions
 Typical study designs: Randomized Clinical Trial
 Individual interventions
o Focus on changing individual behavior
o Example: educating individuals on benefits of quitting smoking