HANNAH BLOCH --- NPR
When it comes to deadly, contagious disease outbreaks like Ebola, the terms "quarantine" and "isolation" take on fresh relevance and urgency. Each has a distinct meaning in the public health context, though the words are often used interchangeably and both refer to protecting the public from communicable illnesses.
Relying on quarantine is a centuries-old strategy to separate the healthy from the sick in hopes of containing infectious disease. The first known formal quarantines went into effect in 14th century Europe to stop the spread of plague, known as Black Death. (The word "quarantine" itself is derived from the Italian quaranta, 40, referring to the number of days the ill were kept apart from everyone else). In 18th- and 19th-century America, quarantines were imposed during outbreaks of yellow fever and cholera. The U.S. Centers for Disease Control and Prevention (CDC) now maintains 20 quarantine stations in the United States, which can detain and examine people — and animals — believed to be carrying dangerous infectious diseases.
A quarantine goes into effect when people have been exposed to an infectious disease but "may or may not become ill," according to the CDC. Since it's not yet known whether they are infected, they're separated from the general population to prevent possible spread of the disease. Pandemic influenza, SARS, cholera, diphtheria, tuberculosis, plague, smallpox, yellow fever and viral hemorrhagic fevers (such as Ebola) are all subject to quarantine in the United States.
Isolation of patients, a more extreme step, can be imposed when people have already fallen ill. In the U.S., this generally means that patients are confined to medical facilities, visits by others are severely restricted, and medical personnel are required to wear protective gear.