Discussions of risk and especially “mitigating risk” have little practical significance for the immunocompromised individual facing down dangerous pathogens. For professionals who manage services they can talk about how in every 100 people maybe 25 will contract a disease in a certain environment. But for the individual who does contract the disease the risk is always 100%. A person does not get 25% of a disease. So, the only way to “manage the risk” for the individual is prevention; to use PPE, hazmat suits or avoid going to areas where those organisms are highly likely to be endemic to the physical environment, like crowded theme parks. Look to the likelihood of harm and the gravity of the harm. If the potential gravity of being ill is severe, the thing to manage is the likelihood of coming across the pathogen and that means full barrier protection or do not go to theme parks. By the way, I think people who are home bound or mostly so can still have a good life.