Isolation is the process in which people who are known to be ill with a dangerous, contagious disease are treated to prevent the disease from spreading. Quarantine is the process in which people who have been exposed to an infectious disease, but are not yet known to be ill, are kept separate from others and monitored.solation lasts for the period of time in which a disease is considered infectious. Quarantine lasts for the incubation period for the disease, after which officials can be certain that an individual is not infected.