You're all doing absolutely brilliantly
You really have come a long way in a short time, well done
OK, so moving on...
I can understand that you want to hold where you are for now due to the illness, you move on when you feel it is time.
What I will say, usually with GW you keep moving forward. If you pause for too long on one particular step LO will become accustomed to this as the new rule and will then become more upset when you change the rules again (it may lead to another 3 days of screaming). When you keep moving forward in small steps it's kind of 2 steps forward 1 back because he gets upset you go back a bit to reassure but then move on again, this way you don't get 'caught' or 'stuck' with falling to sleep requiring this or that prop.
My advice would be to look at the hand holding. Are you holding his hand or is he holding yours?
You might consider this is something you can still move forwards on even now, even though he is a bit poorly (because you are never leaving him without support, you are always responding when needed), if you don't feel ready that's fine, just take into account what I've said above.
The hand hold then, if he has hold of you and it's a pretty tight grip you need to change this next. If he wants to hold something get something else into his hand for him to grip and keep your hand very firmly on him, reassure with your voice "it's ok, you hold teddy/muslin/lovey I'll hold you, I'm right here." If though you have hold of his hand you are already the next step on, gradually reduce the pressure of holding, you can still begin every sleep with firm pressure but reduce the pressure in a more rapid way, begin to take your hand off and put it back without him having chance to be upset, then take it off and return it if he makes noise (and perhaps use your key phrase at the same time or "it's ok, you're going to sleep now"), after returning your hand keep a thought to removing it again. It's a backwards and forwards thing, reassuring then removing.
Once you are able to let go of his hand and he falls to sleep I will suggest the next step is to say "night night, call if you need me" and leave the room. You don't know until you try
If he screams blue murder then resettle and consider taking slower steps...but I think this is worth a try because by you returning he learns something else, that you always return when he needs you and this is a great point of trust, he doesn't 'need' to keep you in the room because you will always always come back. Return without delay (I would only go as far as outside to door in these early days), use your voice "I'm coming" "I'm back" take his hand if that's all that is needed and say "it's ok, you're going to sleep" etc. At any stage it is still ok to pick up if he is very upset or ill or any reason you feel you want to pick up, there is no problem with this, only once he is ready you put him back in his cot, do your usual soothing (hand holding, key phrase) and move on and forward.
If it turns out you need to move slowly from the room stage by stage we can cover that when needed - it might be that you let go of his hand and move a foot away and wait (returning to his hand as needed then returning to your position) or it might be that you can begin the withdrawal by regular WD and comfort, key phrase, I'm going now call if you need, leave the room, even if you return half a second later. Let's see what's needed by his level of confidence or upset when you try it.
You might also use the phrase "I'm going xyz/kitchen/toilet, I'm coming back" and "I'm back" during the day. This key aspect of telling him you are leaving and that you will return, then telling him you have returned may be useful for the sleep time confidence.
I hope you have managed to miss this nasty bug - and healthy vibes to your boy and DH, hope they are feeling better x