Health Status is part of the Citizen Menu and it is a very crucial element in Vampyr. Jonathan E. Reid should watch the citizens health and find a cure, should they be ill. This not only will bring up the living's Blood Quality, but also keep the districts safe.
There are six Health Status levels: Sanitized, Healthy, Stable, Serious, Critical and Hostile.
Once a district turns to hostile (worst case!), the point of no return has been reached and the area will be swarming with dangerous encounters from now on throughout the rest of the game.
This status will also affect which ending is gained upon completion of the game.