Basic notions in epidemiology

HI. In this VIDEO you will learn what Epidemiology is, how it works and what it is for. The term EPIDEMIOLOGY comes from EPI (that means upon) DEMOS (that means people) and LOGOS (that means study of).

SLIDE 2,3,4,5 Epidemiology uses data, numbers and statistics to: 1. Identify new diseases and study their natural history 2. Provide descriptive analysis of events 3. Identify causes or risk factors of diseases, and factors that promote health 4. Evaluate the impact of preventive actions

SLIDE 6 You immediately recognize an epidemiologist at work: sits in front of a computer and looks at numbers, tables, calculations, statistics and graphs. In the past … this was done by hands, with pen and paper. SLIDE 7,8,9 There are two main branches of epidemiology. The Descriptive asks questions like WHAT, WHERE, WHEN something happen or HOW MANY are involved … .. the Analytical asks the question WHY events HAPPENS and tests hypothesis by mean of organized studies.

SLIDE 10, 11 One example : Descriptive Epidemiology establishes frequencies, rates and incidence of smokers and people with lung cancer (on the left) While Analytical Epidemiology attempts to put in relation the two, and establishes IF exposure to sigarette smoke CAUSES lung cancer, or CONTRIBUTES TO, or not at all … (on the right). You all know the answer to this.

SLIDE 12-13 Another example: descriptive epidemiology establishes rates of plastic production and waste in the environment and also establishes that, at the same time, there is reduced sperm count in the male popolation (see above). Analytical epidemiology investigates the possibility that ONE (the plastic) MAY CAUSE THE OTHER (the sperm count) or concur to it (see below).

SLIDE 14 The reality is: health problems can have several causes. Analytical Epidemiology applied on populations aided by statistic tries to separate ONE factor at a time, and search for a link. Then, can examine the causing factors together and suggest which ones appears more relevant, and which appears less relevant. Isn’t this fantastic?

SLIDE 15-16 Within analytical epidemiology there are two types of studies: 1. the Observational studies – such as cohort studies, and 2. the Experimental studies – such as clinical trials for medicines. SLIDE 17 Experimental Studies are based on solid and reliable scientific methods (that you will see in Week 5). Typical experimental studies are clinical trials, field trials, and community trials. SLIDE 18 Oh, HI Neil, and HI Joe. Do you have a question? “YES soo… why do we need epidemiology… if we already have chemistry and biology.. that can tell us everything?“ Eh MMmh … YES and NO. Let me answer right away. SLIDE 19 Chemistry and biology tell us something but not all. And epidemiology tells us somethinng but not all.

In human, the experimental studies can be used ONLY for therapeutic or protective exposures. We cannot do experiments treating people with chemicals. WE ALL AGREE ON THAT, RIGHT? For human, is a lot more important to know if WE are at risk, in real life, with real exposure. Also for animals.. there are many legitimate ethical concerns and interspecies differences to limit these studies to the strictly essential. SLIDE 20-21 Observational studies are essential when dealing with humans since testing on human is unethical. We can only observe, note, extract data, calculate and find relations.

The study can follow the course of time, so it starts from exposure (for example exposure to a chemical substance or air pollution) up to observing after some years a health

effect such as a cardiovascular disease or elevated body mass index: these are the cohort studies. Otherwise in case-control studies, a study can start from a health effects already present, and investigate a possibly associated exposure, looking backwards. SLIDE 22 In both cases we can calculate HOW MUCH exposure contributes to the observed health effect. We can establish the risk of getting sick in relation to an exposure!

To do this, two very important calculations are done : the Relative Risk and the Odds Ratio. We can find that an exposure can increase the risk of disease or it can be protective, or it can also has no effect. In this way we don’t really find the causes of disease but we have a first hint SLIDE 23 There is a new emerging branch of Epidemiology, that focuses on the biological plausibility of specific exposure events once these have been linked to disease conditions. WHAT HAPPENS INSIDE AN ORGANISM FROM EXPOSURE TO DISEASE? SLIDE 24 Molecular epidemiology can establish different end-points, related to exposure, up to disease. This science is very interesting!

It has the possibility to look into something complex, discovering the steps that gradually go from exposure to disease.

One strong limit of this approach is the individual susceptibility: each individual responds differently to the same exposure.

SLIDE 25 Back to our theme: endocrine disruption. It has been first hypothesized by epidemiology, and only after we got some chemi- and bio-data in support of this.

An endocrine disruptor is: an exogenous substance of mixture that alters functions of the endocrine system, and consequently causes an adverse health effect in an intact organism or its progeny. In the article that follows (Week 2 Activity 2 step 3) we will show you some of the evidence linking endocrine disruption and with global health issues.