Hygienist

This passive skill mostly serves as a psychological defense against conversion, as will be reluctant to try and infect you at a 50% chance of wasting their.

When targeted anyway, or unintentionally through food or traps, the resistance means that it takes an average of 6 spores to be converted (or 8 with Mushovore Bacteria). So Derek can afford to be a little less careful in that regard, if that increases his efficiency, or even act as and actively try to spring traps intended for other people.

The illness resistance is nice too, and can save you some trouble especially when eating spoiled food. Though it also means it is harder for Derek to be proven human through diseases.