What you need to know about infectious deseases - an excellent article

Many people think of bacteria, viruses, and other microorganisms as our enemy. The germ theory of disease, first proposed in the 19th century, maintained that illness springs from the actions of infecting microorganisms. Germ theory was crucial in identifying many diseases caused by microbes and in finding ways to prevent them through such measures as immunization, sanitation, and improved living conditions.

What you need to know about infectious deseases