Sam and the other survivors, George, Jack and Darla, had arrived at Chicago two hours ago. Obviously thats not nearly enough time to go through all the nooks and cranneys, but the megaphone Jack had brought along would ensure anyone within a three mile radius could hear, and so would the zombies. After a few drive-bys on some zombies, they'd given up with Chicago.
The only shred of hope they'd had was a message blaring that some Russians had escaped Army custody and were to be shot on sight. Sam preferred not to use violence, at least not on humans, so he ignored the last part.
If he knew anything, the Russians would probably look for some survivors, either out of charity, or for some nefarious reason. Sam hoped for the first one. Even better, he'd heard another message saying that Washington D.C. was a safe zone for anyone who could reach it.
Sam decided that a large group of Russian Army Forces would probably be better than some assurance of safety. Just look what it did for Chicago. Besides, Maybe he could ask them some questions on the virus itself.