FIGHTING CONTAGION

See that the privy is kept clean inside and out, or take the blame on yourself if some member of your family dies of Typhoid Fever.
- Walker County Board of Health poster, c. 1930

Long before the germ theory of disease was postulated or proven, people observed that disease could be contagious — spread by direct and indirect contact with the sick. Quarantines, for example, were used in 14th-century Italy to combat the plague, and travelers were shunned, clothes of the dead were burned, and the streets were cleaned of refuse in order to reduce contagion.

As the microbial world became better known, the precise mechanisms of disease transmission could be studied and more fully understood — and the protective measures against disease became more directed and more effective. It is now common practice for people to be tested and screened for specific diseases and for perishable foods to be monitored for contamination. One of the simplest measures — hand washing — is also one of the most effective.

Left: Culture of a human handprint, showing bacterial contamination.

Right: Photograph of a sneeze, showing airborne droplets that can contain microorganisms. A strong sneeze can propel droplets at speeds of up to 200 miles per hour.