Why should I as a hypothetical employer be particularly keen on hiring someone who has taken extended leaves of medical absence? There is a strong financial risk and no reward for doing so.
So if I ended up with a one-time sickness that put me up in the hospital for, say, 3 months, then I'm more likely to catch another long-term sickness than the rest of the general population? Logic!
In the individual case the probability can only be calculated by a physician.
In the general case? I am sure (to a certainty sufficiently high to factor into hiring decisions between otherwise equally qualified candidates) that the increase in probability it is non-zero. So yes, I am saying in the general case that people who have been seriously sick before have an elevated chance of being seriously sick again.