This isn't a different answer from @mkt but a graph won't fit into a comment. I fit a logistic curve in Stata (after logging the predictor) and get this graph


[![enter image description here][1]][1]

An equation is 

100 `invlogit`(-4.192654 + 1.880951 `log10`(`Copies`)) 

EDIT: Essentially just an indication of technique. Separating the two viruses is, as mentioned elsewhere, a next step. 

  [1]: https://i.sstatic.net/KzBZG.png