CD4 and infection: Then, the time from date of infection to CD4 testing for an individual i can be estimated by\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document} $$T_{i}=\frac{\sqrt{\text{first} CD4}-a_{i}}{b_{i}}.$$ \end{document}Ti=firstCD4−aibi.