Complex sentence: Isolation refers to separating those who are sick from those who are not, whereas quarantine refers to separating those who may have been exposed to a disease until they either show signs of sickness or are no longer at risk.
Split into simpler sentences: Isolation refers to separating those who are sick from those who are not. Quarantine refers to separating those who may have been exposed to a disease until they either show signs of the disease or are no longer at risk.