Infectious Diseases and Bioterrorism

Microorganisms are a necessary part of everyday life. Many, known as resident or normal flora, adapt and live peacefully with the human body, providing benefits such as vitamin production or cellulose digestion in the intestines, and protection from disease-producing pathogens. Transient flora may stay for weeks to months but do not remain permanently because of fierce competition from resident flora. When the delicate balance between the host and normal flora is disturbed, infection occurs. Endogenous infections arise when normal flora contaminate tissues or body areas not usually occupied by the organism, such as skin bacteria entering tissues through wounds or insect bites. Exogenous infections arise from outside sources such as soil, water, animals, or the hands of health care workers. C H A P T E R 6