Disease
Disease occurs randomly in cities which are overpopulated or has unemployment.
To cure a city of disease, Antitoxins are necessary. The lower the TL of the Antitoxins, the more is needed, depending on the "TL" of the disease. The city will show in the city reports how many Antitoxins are required.
It is dangerous to leave the city diseased, if carried on too long it can lead to decay.
Passengers loaded from a diseased city will have the disease.
The avatars topic describes the effect of diseases, under the Afflictions heading.