I’m terribly sorry! I see what your questions was but the they were ambiguous. Again, my presumption was Stalin would hold a major city like that not for namesake (or just) but because it was the last real port across the Volga, and the Germans could not be allowed to fortify the Volga banks because it would give them great freedom of maneuver, including consolidation.
My guess, and this is total speculation is that the outbreak largely burned itself out among the civilian population before the 6th army arrived, because soldiers were taken out of the 6th army before encirclement because of wounds or scheduled leave (the Germans were very strict about keeping this to reduce operational exhaustion, a term which includes more than PTSD) mention a lot of things, but getting sick isn’t one of them.
And there were quite a number of these men right up to the day before Uranus began. There was a guy on Quora who wrote about his grandad having leave scheduled the day before, and the paperwork was FUBARED, and this was before you could check on computers, and his superior officer overrode the protocols and let him leave early because this was scheduled and clearly an administrative hiccup. And it saved his grandfathers’ life. Although that guy was artillery outside the city, but no mention of a plague.
I wish I could be of more help but the problem with being an autodidact on things is when you have knowledge gaps, they can be severe and you’ll never even know it until you need to know it. Then it’s pants around the ankles time.
I hope someone who’s more knowledgable can help you on your quest for knowledge.