At first, he refuses to cooperate with Gabriel to obtain a diagnosis, and Gabriel must do everything he can to prove to the 'geezer' that they need to run tests. The first diagnosis in phase one is acute liver failure. The player then begins phase two, and Gabriel makes a grim discovery. Jacob's official diagnosis is Dilated Cardiomyopathy, a form of heart failure where the heart enlarges and becomes weaker. The DCM is a result of Viral Myocarditis that Jacob had two years ago. Despite Gabriel's recommendation for a heart transplant and to retire and wait for a donor, Jacob pulled some strings and arranged for an OLCVR (Overlapping Cardiac Volume Reduction Operation) or usually called the Batista procedure to relieve his symptoms. This is CR-S01's first surgery in the game. The procedure did not involve removing the affected parts of the left ventricle, but rather to overlap the cardiac muscle to "shrink" the heart. Gabriel was against using this procedure, since it is an old procedure that does not completely cure the disease, but simply just buys the old man some time.
During "Patient Zero", Jacob asked Gabe to diagnose a USAMRIID researcher (Samuel Trumbull) who has been infected by the Rosalia Virus. During the diagnosis, Gabe is stopped by the Army, which intended to stop him from exposing the information about the virus to the public. Jacob then orders the diagnostician to be arrested. However, in reality, he organizes Gabe's escape with RONI's help, and is arrested himself soon after.
After the Rosalia Virus pandemic, Jacob is revealed to still be alive, and after Gabriel has asked him what he wants on his tombstone, answers: "I can't die. You owe me, remember?"