“…To understand how models are currently used to represent the progression of this disease, we considered 40 recent models of within-host dynamics, all of which are expressed as nonlinear systems of differential equations. Of these models, one used stochastic differential equations Wang, Liu, Xu & Zhang (2015) and eight used delayed differential equations (Huang et al (2016) , Alshorman et al (2016), Pitchaimani & Monica (2015), Sahani (2016), Balasubramaniam et al (2015), Elaiw & Almuallem (2016)). In addition, the focus of several of these papers was somewhat different from ours.…”