My character got sick with the Flu but quickly cured it by keeping my water and hunger levels high. As soon as my energy and water stats would drop (between 1500 - 800) and my immune system went below a certain value I would get the sickness again. Tried it with a different character and even from a different account and it still happened, but I don't know if it can be reproduced 100% of the time. It happened both in Official and Community servers.