I second Jess, with one exception - if you're well within a week, I think you could try one last long run before you start your taper. The mental confidence you'll gain IMO will outweigh whatever you lose by cutting your taper to three weeks instead of four.

Remember the balance you're trying to strike isn't about working out as though you were well. Unfortunately, that option is gone. It's about "how much fitness will I lose if I depress my immune system, draw microbes deeper into my lungs by hard breathing, and stay sicker longer?"