Maybe some people are unaware of the fact that infected player (with cholera, salmonella or flu) will contaminate bottle/container from which he drinks even if bottle remains empty. You can put then drinkable water, still not good, that container is contaminated and will infect anyone who drinks from it. Same is with food or meat if you share between players. Using purification tables will remove all agents, disinfectant alcohol will remove all except salmonella. Also boiling will remove them all.
Even antibiotics can be contaminated with agents from previous player who used them.

Especially for players who live in same base, quarantine must be treated with maximum seriousness. Disinfect all containers after you are sure that everybody has fully recovered and no one is still sick.