Medical leave

Why is it some employees always ends up falling sick and taking medical leave as soon as they return from their long vacation? I have observed some employees in my department that are more prone to taking medical leaves compare to others. Guys in particular who are still liable for reservist seems to use up their medical leaves compare to employees who are not liable for reservist! There are some who are more prone to ill and taking medical leaves either on Mondays or Fridays, how interesting isn’t it?

I feel those who are healthy should be rewarded for not taking too many sick leaves. Perhaps employers should reward those who are healthy by granting the opportunity and option to convert unused sick leave into paid leave. Otherwise, those who don’t take many sick leave would feel short change, after all, there are 14-paid medical leaves per year entitle to employees in my organization and without option to convert unused sick leave to paid leave, might as well as used up the 14 days sick leave isn’t it?