This
post entitled "Bring out Your Dead" is an analysis of the "mini-game" within the Twilight: 2000 v2.2 rules dealing with disease.
Reading through the background material (resulting disease helps drop the world population to 50% a lot more than the actual armed conflict) and the actual tables, I'm left thinking disease should be a common challenge in the average Twilight: 2000 campaign, particularly one set in Poland where there is still low-level conflict...