Slimelung germs can be found growing in polluted oxygen or slime. They multiply quickly in Slime, Polluted Oxygen, and Polluted Water but die in most other gasses and surfaces. Germs die quickly when exposed to Chlorine and can be removed from slime with an Ore Scrubber.
When inhaled, slimelung germs build up over time and reduce the Duplicant's immune system. Once this reaches zero, the Duplicant contracts the disease Slimelung. This disease is fatal in 8 cycles if untreated, but each treatment resets this timer.
While inflicted, Duplicants need more breathable gas than normal and can suffocate in low-oxygen areas. They will cough sometimes and often need to recover breath, which will interrupt any activity (including receiving treatment). Coughing releases 1000 Slimelung germs into the environment, but these are mostly harmless in such small quantities, provided the room is not full of polluted oxygen.