We had the experience of having our whole partially-finished basement get infested. I had installed fiberglass insulation between the studs and covered with poly sheeting stapled to the studs. The first winter, a number of mice got in through a gap in the framing. They started a number of families. I would estimate at least 30 or 40. The insulation was soaked with urine. I ended up stripping out the plastic and insulation, but of course the smell remained. I sprayed a bleach solution of 4 parts water to one part normal-strength bleach (5.25%), then dried it with fans. I then did it a second time about a week later. That did the job.
BTW, don't be tempted to use a stronger bleach solution, as stronger than 3 to 1 will break down the wood fibers. I found that out the hard way when I was removing mildew from wood siding.
2008 Itasca Meridian 37H & 2015 Flagstaff T12RBST
2011 & 2012 Len & Pat's "One lap of America"
27K miles & 41 states in 13 months - Woo Woo
Yellowstone Lake 6-1-2012