SEIR compartmental model of infection incorporating quarantine and isolation measures. The class E represents a latent class during which an individual who has been exposed to the pathogen is not yet infectious and is asymptomatic. Individuals who might have been exposed (S and E) are quarantined and proceed to the respective Q classes: QS and QE. When susceptible individuals in quarantine (QS) are determined not to have been infected they are returned to the susceptible class (S). Those in quarantine who develop infection (QE) are isolated and proceed to class (QI), as do infected individuals (I).