To contain the spread of a contagious illness, public health authorities rely on many strategies. Two of these strategies are isolation and quarantine. Both are common public health practices that aim to lessen the likelihood that people who are sick will spread their illness to others. Sometimes these measures are voluntary, and sometimes public health authorities make them compulsory.

Isolation applies to those who are known to have an illness, and quarantine applies to those who have been exposed to an illness but who may or may not become ill.

Isolation means separating people who have a specific illness from those who are healthy. This allows the sick person to be treated while the healthy are protected from infection. People in isolation might be cared for in their own homes, in hospitals, or in designated healthcare facilities. Most of the time, isolation is voluntary. If necessary, however, federal, state and local health officials have the authority to compel sick people to be isolated in order to protect the public.

Patients with tuberculosis, for example, are routinely isolated when treated in hospitals today.

Quarantine means separating and restricting the movement of people who, while not yet ill, have been exposed to an infectious illness and might become ill.

Oregon can declare and enforce quarantine within its borders. The CDC can detain, medically examine or conditionally release people suspected of carrying certain communicable diseases.

During the 2003 global SARS outbreak, the CDC asked people who were exposed to SARS but had no symptoms to voluntarily quarantine themselves (in other words, stay at home), monitor themselves for symptoms and seek medical attention if any appeared. These steps helped control the spread of the disease.