Paperback Probably from the 80s. Cover may have had the exterior short of an office tower (~20 floors) with a man suspended on a rope swinging outside.
Man goes to his companies office in the tower, (The building is pretty deserted, its either a holiday, or after hours/early morning) He is in a side room (Snack room? Xerox room? Coffee break area?) when he sees armed men walk past toward his office talking on the radio clearly looking for him.
So now he is dodging around up and down to various floors trying to avoid the armed men. He can't call out, (Phone lines are cut) or use the elevator (they have either shut it down or put it in emergency mode where it will only go to the ground floor where they have more men waiting)
Somewhere along the chase he gets rappelling gear (I think from breaking into an Adventure Outfitters Shop office, or taking if from one of the men whom he is able to ambush) and using it to transfer to another floor, by rappelling down the elevator shaft, or the outside of the building. (i.e. they know he is above 16th floor, have men stationed on 15th, so he repels down to 12th to leapfrog past them.
It turns into a Die Hard type situation, with him scrambling around trying to avoid them and/or take them out. (If I recall correctly, except for the team leader, they are not highly trained special forces types, just well trained and armed Security guards.
Why they are after him. From overhearing them, or hearing them talk on a radio he got from one of them he ambushed, or by talking with them over the radio he got from one of them. They tell him why they want him.
Apparently a day or two before the story stats, while visiting a research lab in the course of his job. (or visiting a facility that had a secret research lab) He became infected with a deadly virus. I think an animal got lose and either scratched or bit him or more likely got lose and contaminated some object that he later touched. Because no one at that time he is there realizes he was infected until they review the tapes after he has already left.
The virus he has contracted is Lethal, has a short incubation period, a highly contagious period, then after the contagious period stops rapidly breaks down your body and you die a few days later. (ie, 3 days after exposure, you can pass the virus to anyone through contact or fluid exchange (Kissing, splatter with blood, spitting, coughing on them) but that phase only last 2-3 days, after that you can not spread the virus, but your going to be dead in a couple days.
I believe the men after him are the security team from the research lab, who are trying to kill him BEFORE he becomes contagious. But do NOT want the authorities know know about the situation. (Lab was doing illegal research?)