How can I mitigate disease?

Vitamins are reported to prevent disease from getting worse. Also, having a higher Might stat reduces the risk of disease. Increasing your Might stat past 50 or 60 should help significantly. Engineer and Scouts are more susceptible to disease because of their lower Might stats.

Source: Steam Forums and Steam Forums

In terms of mitigating disease, the Might stat is the one that is checked when a resistance check is made, and hence decides whether you reduce, maintain, or increase your disease level. Having a high Might will make you less likely to die of disease, and also poison.

That's the only disease mitigation I know. There are disease curing items in game, such as ;
Antibiotics - Random drop, some classes start with some, can reduce two levels of disease
Aggressive Antibiotics - made by combining Anti-Bodies and Moldy Bread at a Cooking Station or with an EZ Cooker, can reduce four levels of disease
Terran Med Kit - Random drop, some classes start with it, has five uses, each use can reduce one level of disease
Improvised Med Kit - made by combining Antibiotics, Bindings, Bone Slivers, and Serum at a Lab Station, has five uses, each use can reduce one level of disease
Vitamins - Random drop, very rare, has other possible uses, increases your chance of succeeding the next disease check (i.e. not a guarantee)
Immunojolt - Random drop, high medicine check, immunity to disease for a time, cures any existing disease
Immunoagent - Random drop, immunity to disease for a time, cures any existing disease
Resistance Booster - Random drop, increases your chance of succeeding the next disease check (i.e. not a guarantee)