Low immunity diseases
Low immunity diseases are diseases that are inflicted based on the hidden health stat. This stat is similar to hunger and thirst, but will tend to recover on its own when below zero. In 0.C (Cooper), most health changes come from comestibles.
The Disease Resistant trait reduces the chances of catching these diseases, and the Disease Immune mutation makes the character immune to them.
Currently ambient diseases include only the Common Cold and Influenza. Both are announced upon successful infection and visible on the @-screen. You cannot get both diseases simultaneously and their durations do not stack.
When infected, there is 16% chance the infection will be the flu for 40000-80000 turns (something around 2.5-5.5 in-game days), otherwise it will be the common cold for 20000-60000 turns (around 1.3-4.1 days). Both are infected with 3 strength, which means that mouth protection helps, and moreover if you wearing a gas mask permanently, then you are immune to ambient diseases too!
Both of these diseases increment the thirst counter every 300 turns. They also cause coughing with a 0.(3)% per turn. Coughing creates noise with 12 volume (as loud as a flashbang explosion) and costs 80 movement points.
Their symptoms can be eased with Non-drowsy cough syrup (for 6000 turns per pill), Cough syrup (for 7200 turns, plus 30 fatigue), and Bee balm tea (for 6000 turns per dose, plus 1 stimulant, +2 to Strength, +1 to Dexterity, Intelligence and Perception) medications. Both can be fully cured with royal jelly.
Note that medications can be detected by Blood Analysis ("Antihistamines") and accidentally removed by Blood Filter bionics.
Common Cold
It decreases the character's strength by 3, intellect by 2, and dexterity and perception by 1 (medications reduce the penalties to strength and intellect by one).
Influenza
It decreases character's strength by 4, dexterity and intellect by 2, and perception by 1 (medications reduce the penalty to strength by 2 and intellect by 1). There is a 0.02% chance per turn to vomit (plus additional 0.03% chance with Weak Stomach and 0.04% chance with Nausea) - if the character is on medications, there is a 50% chance they will negate the vomit.