Infectious compartment
= Infectious compartment
{title2=$i=I/N$}
The <infectious compartment> consists of people currently able to transmit <infection>. In the closed <SIR model>, $I(t)$ is their count and $i(t)=I(t)/N$ their <fraction> of the fixed total $N$. The <SIR model> has no separate delay between acquiring <infection> and entering the <infectious compartment>; the <SEIR model> adds such a stage.