Determining Agent Orange Exposure
The case of the Vietnam veteran's exposure to dioxin through Agent Orange
presents the most complex epidemiological problem ever imagined. The test
is this: How do you determine, among 2.5 million Vietnam veterans, who was
exposed to Agent Orange, to what degree and extent, and what if any, is the
resultant harm of that exposure?
Some of the difficulties encountered when confronting this problem include:
1. An estimated 2.5 million men and women served in Vietnam. During their
tour or tours, they may have been highly mobile, moving about the
countryside throughout an area as big as the state of California. Tracking a
single individual for every day of their tour is extraordinarily difficult,
tracking large numbers is almost impossible.
2. How can exposure be quantified with precision? "Exposure" in
epidemiology means the person had the "opportunity" for contact in some
manner with the chemical. But what is contact? Does this mean direct
contact, such as physically being sprayed with the products, or does it
include more remote opportunities, such as contact through airborne
particulates, or contact through the food and water chain?
3. Degree of exposure: This is sometimes called the dose/response factor in
science. In order to estimate the health effect of an exposure, it is useful
(some say critical) to be able to estimate "how much" exposure a person
may have had, in quantity, frequency, and duration as well as means of
exposure.
4. Effect: Science looks for "cause and effect" in determining health
outcomes. If is extremely difficult to accurately state that a behavior or
exposure causes an outcome. For example, it is widely accepted that cigarette
smoking may cause lung cancer, but this does not account for those who
smoke for years and never get cancer, nor those who never smoked and get
the disease.
5. Delay: Many diseases, including cancer, have extremely long latency
periods. It is possible, therefore, for a person to be exposed to a toxin, and
not have the effect of that exposure manifested for twenty years or more.
During the years, however, a person may have been "insulted" with other
additional exposures through the workplace or the environment. It becomes
extremely difficult assessing and separating these "confounding" exposures
when looking for the source of a disease.
Keeping these difficult criteria in mind, we shall next examine the efforts at
studying the effect of Agent Orange exposure.
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