Environmental Engineering Reference
minor or less severe disease in humans. Some strains of the following bac-
teria have are common causes of disease associated with exotoxins: E. coli ,
Staphylococcus aureus , Streptococcus pyogenes , Clostridium perfringens ,
Shigella spp., and Clostridium botulinum .
LC 50 The median lethal concentration of a substance in the air, causing
death in 50 percent of the animals exposed by inhalation; a measure of
LD 50 The median lethal dose, causing death in 50 percent of the animals
exposed by swallowing a substance; a measure of acute toxicity.
Neurotoxin A toxin that attacks nerve cells (e.g., botulism).
Noninfectious or noncommunicable disease The chronic, degenerative, and
insidious disease that usually develops over an extended period and whose
cause may not be entirely clear. In its broad sense, cancer, alcoholism,
mental illnesses, tooth decay, ulcers, and lead poisoning are regarded as
noncommunicable or noninfectious diseases. Also included are cardiovas-
cular diseases, pulmonary diseases, diabetes, arthritis, nutritional deficiency
diseases, malignant neoplasms, kidney diseases, injuries, and illnesses asso-
ciated with toxic organic and inorganic chemicals and physical agents in
air, water, and food. For the purposes of this text, discussion of noninfec-
tious diseases emphasizes the environmental media or factors serving as
the vehicle for transmission of the disease. The usual environmental media
are air, food, water, and land (soil, flora, fauna); other factors leading to
injuries and contact may also be involved.
In contrast to communicable diseases, chronic diseases may be caused by a
variety or combination of factors that are difficult to identify, treat, and
control. The resulting illness may cause protracted or intermittent pain
and disability with lengthy hospitalization. A degenerative condition is the
result of the deterioration or breaking down of a tissue or part of the body
Pathogen An infectious agent capable of causing disease.
Pathogenic The potential for producing disease, if the organism is sufficiently
virulent to enter the body and overcome the defense mechanism of the host.
Prevention, primary Prevention of an etiologic agent, substance, or action
from causing disease or injury in humans; intervention; regulation of expo-
sure to environmental hazards that cause disease or injury to decrease
morbidity and mortality. Action to promote health and prevent disease or
injury. Includes immunization, adequate supply of safe water and basic
sanitation, prevention education, food and nutrition, and maternal and child
Prevention, secondary Early detection and treatment to cure or control dis-
ease. Surveillance, screening, and monitoring the environment. Also mea-
sures to protect the public (e.g., treatment of public water supplies, fluori-
dation for dental control).