I think the standard advice is to keep the intensity up but decrease volume.
It's frustrating though. I went with 5-3-1 just to maintain weight and lifts. In less than 2 cycles I had dropped off significantly on my squat. Granted, I lost a little bit of weight when I got sick but I've put that back on gradually.
I think I'm slowly starting to build the squat back up, I'm also going to add a second squat session every week. You'll have to find that balance for yourself. In my minuscule experience the squat drops off fast when you lower the volume and that's compounded when you are restricting calories (or sick).
Good luck.