Are the present concerns about contracting a disease in the future a reality?

The suspicions that come to your mind are merely whispers (waswas) and delusions, so do not pay attention to them. Satan is eager to sadden the believer to deter him from righteous deeds or to make him think ill of his Lord. Repel these whispers, and seek refuge with Allah from the accursed Satan. Remember that what has befallen you was not to miss you, and what has missed you was not to befall you. Allah Almighty says: "No disaster strikes upon the earth or among yourselves except that it is in a register before We create it — indeed that, for Allah, is easy — In order that you not grieve over what has eluded you and not exult over what He has given you. And Allah does not like every self-deluded and boastful one."