ABSTRACT
This is an important chapter because here is where we begin to look at the principles of infectious disease. Armed with the things we learned in the previous chapters, we are well prepared for these discussions, and the things we learn here will become part of the foundation for all of the other topics we examine. Our discussions will be broken down into three major parts. The first will examine how infectious disease can get started, which is referred to as its etiology. The second will examine how disease can develop, including communicability and contagiousness. The final discussion will be about infections that move into the systemic circulation.
