Environmental Toxicology Diary

Epidemiology study is the study of the causative factors of an ilness or disease. These causative factors are associated with the incidence and distribution of disease within a specific population. So basically, it is just as same as toxicology study, both are aiming the same objective, finding out the etiological factor of a disease. What interesting is epidemiology study is held in a real community, real world application. You have to survey using questionnaires, get answers about their common things.

Basic principle on how to determine the population is to find their common characteristics such as same occupation, same area of residence or even same water company supply. You determine by your self what specific groups you would like to include in the epidemiology study, of course that have to be adjusted accordingly with what kind of particular disease you would want to find the causative agent.

Epidemiology study has been proven to be useful in determining causative agent of disease such as heart disease, cancer and stroke. Now why this can be succesful? It is because the large numbers of people, groups can be studied which then the data obtained are representative in terms of exposure of specific causative agent and the effects are observed in a daily life. This kind of study in some extend is very useful especially when there is not enough data obtained from toxicology study. Even though that data is adequate, still extrapolating the information from animal experimentation has become another problem.

A very simple example is well shown with the occurence of cholera in 1849 identified very well by John Snow in London. During the outbreak of the cholera at that time, Snow observed that the occurrencen of the disease was higher in some areas in London than others. So he did a quick investigation, and he found out that these residency areas were supplied their water from two water companies, the Lambeth Company and the Southwark and Vauxhall Company. For the information, both companies were using Thames river as a water source, which was heavily polluted with sewage.

Prior 1854, Lambeth Company moved his intake to a less polluted portion of Thames River. Snow gathered all the historical data such as the number of household supplied by both companies and calculated the number of deaths from cholera during the first seven weeks of the epidemic compare to the rest of London. He found interesting fact that higher mortality rates was observed in the household that water was supplied by the Southwark and Vauxhall Company (315 deaths per 10,000 households) than households that obtain water from the Lambeth Company. So he finally began to conclude that the cholera was associated with the water source which was polluted with sewage, that happened in 1854.

Epidemiology study can also be used to determine causative agent of noninfectious diseases. For example the relationship between cigarette smoking and the development of lung cancer. This was pioneerly investigated by E.C Hammond in 1966. More than 1 million participants were involved in this study, and he found that the higher the number of cigarettes smoked per day the hgher the risk of dying from lung cancer.

Several attributes of epidemilogical study are:

First, epidemiological study usually involve a comparison between two or more groups of population. The may be divided based on observed response or effect or based on what kind of substance they are exposed to. There are so many options you can pick and determine, just make sure measure the observed effect of each group and provide another group that does not provide any effect and this group acts for a controlled group.

Second, often there is no clear information which specific cause-effect relationship can be established, usually this happen when involve noninfectious agent such as toxic metals or chemicals. Thus, epidemilogy only provide an association between a certain causative agent and the observed effect. Just look at the example above, in the cholera example there was a strong association between individuals who had cholera with the water supplied so it was relatively easy to conclude that sewage contaminated water was the direct cause of the cholera.

How about nonifectious agent? It is often difficult to determine the cause-effect relationship for toxic substances when most of them involve a long period of time between exposure to the substance and the development of the disease such as cancer or heart disease. However, there are some instances that a specific disease closely related to one toxic substances, for example the forming of lung cancer called mesothelioma. It occurs to individuals who get exposed extensively with asbestos, although not all exposed with asbestos develop mesothelioma.

Third, the information from epidemiological study may be inaccurate or even incomplete. If you are studying the disease by sampling a specific groups exposed to a certain chemicals for many years, often when you ask them questions about that, not all information can be well recalled. This varies depend on each memory ability to recall their daily life and habits where exposure to a causative factor occurred. The level of exposure is uncertain as well, thus only association between the illness and the causative factor can be established.

Bookmark to: