Environmental Engineering Reference
In-Depth Information
or organization. Collaborative efforts from different public welfare sectors are
necessary to make meaningful improvements in public health.
It bears mentioning that many bacteria live in symbiosis (mutual benefit)
with humans, with both deriving mutual benefits. The presence of natural “flora”
of the intestinal tract and skin are normal and considered healthy under most
circumstances; when the immune system becomes compromised (i.e., with age,
HIV infection, breaks in the skin, chemotherapy, etc.) these organisms can cause
pathological disease. The bacteria also provide protection against more damaging
bacterial and viral organisms and can become depleted with the use of antibiotics.
When we refer to “infectious diseases” for the rest of this chapter and the next,
we specifically mean those infectious organisms that cause pathological disease
in humans.
Life Expectancy and Mortality
The life expectancy at birth has varied with time, geography, and the extent
to which available knowledge concerning disease prevention and control could
be applied. Table 2.1 shows the trend in life expectancy through the ages. The
gains in life expectancy in the United States between 1900 and 2000 shown in
Table 2.2 have resulted in lower childhood mortality and longer life expectancy,
and this is typical of the epidemiologic transition already mentioned. The life
expectancy gains since 1900 are due primarily to better sanitation (water filtra-
tion and chlorination, sanitary excreta and sewage disposal, milk pasteurization,
hygiene), improvements in nutrition, vaccination and the development of antibi-
otics, and improved medical care. These measures have led to a reduction in infant
mortality, the conquest of epidemic and infectious diseases, and an improved
quality of life. Many developing countries have achieved dramatic reductions in
infectious disease mortality among upper and middle class populations; however,
the joint burden of poverty and infectious disease remains entrenched in many
areas, including in the United States. In many areas of the United States, includ-
ing inner cities and Native American reservations, life expectancy is as low as
in countries with much higher burdens of infectious disease. Future increase in
life expectancy in the United States (and other developed countries) is depen-
dent in part on our ability to identify the causes and control the chronic and
degenerative noninfectious diseases such as cardiovascular diseases, malignant
neoplasms, and cerebrovascular diseases, provided we maintain and strengthen
existing barriers to infectious diseases as needed. In the United States, the top 10
causes of death in 2004 were diseases of the heart, cancer, stroke, chronic lower
respiratory disease, unintentional accidents, diabetes, Alzheimer's, influenza and
pneumonia, kidney disease, and septic bacterial infections. 12 See Table 2.3.
The prevention of deaths from a particular disease does not increase the life
expectancy in direct proportion to its decreased mortality. 13 Keyfitz 14 gives an
example showing that if a general cure for cancer were found, there would be
nearly 350,000 fewer deaths per year (cancer deaths in 1970). It would seem,
then, that the mortality would be lowered by one-sixth, since cancer deaths were
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