A total of 21 people have been in contact with patient  positive for SARS COV 2 and these people do not show any symptoms or signs of COVID 19. What is time duration for which they must be quarantined?
Quarantine has been defined as "the limitation of freedom of movement of such well persons or domestic animals exposed to communicable disease for a period of time not longer than the longest usual incubation period of the disease, in  such manner as to  prevent effective contact with those not so exposed". Quarantine measures are also "applied by a health authority to a ship, an aircraft,  a train, road vehicle, other means of transport or container, to prevent  the spread of disease, reservoirs of disease or vectors of disease".
Quarantine may comprise  
(a)  absolute quarantine, as defined above;  
(b)  modified quarantine, e.g.,  a selective partial limitation of freedom of movement, such as exclusion equilibrium between host and environment by encouraging some ecological influences  and inhibiting others.
Period of communicability
Median incubation period
Minimum incubation period
Maximum incubation period