Luke has a compromised immune system. This may have something to do with following Milos' strict 'supplementation diet'.
Luke is constantly dogged by flu's, colds and general low-level viruses. I have been calling on Luke for years to dump both Milos and 'the diet' and to re-explore healthy eating and sensible training.
Unfortunately, it all falls on deaf ears. Luke believes, in some crazy way, that he will be an Olympian, and nothing anyone says will change his mind!