Aplastic anemia refers to a disorder that takes place when the body loses the tendency to generate enough amount of new blood cells. Aplastic anemia is a rare and serious disorder that can develop or arise at any age. In the condition, the person becomes fatigued and possess a greater threat of developing infections and uncontrolled bleeding.
Thus, in the given case, the nurse should appoint a roommate who is free from any kind of infectious disease or any other thing, which can stimulate an infection.
If want a direct answer it would be the decrease in mice, but if you want to get technical the decrease in grain spills caused mice to leave so that would be the indirect cause