Every survivor is scripted to be either normal or infected, only the symptoms are randomized.

Here is every single survivor outcome:

Day 1

• 1- quarantine (scripted)
• 2- survivor
• 3- kill

Day 2

• quarantine guy is a survivor
• 1- survivor
• 2- kill
• 3- survivor
• 4- kill

Day 3

• Nobody

Day 4

• 1- kill
• 2- survivor
• 3- survivor
• 4- survivor

Day 5

• 1- kill
• 2- survivor
• 3- kill
• 4- survivor

Day 6

• 1- kill
• 2- kill
• 3- survivor
• 4 -survivor
• 5- kill
• 6- survivor

Day 7

• 1- survivor
• 2- survivor
• 3- kill
• 4- survivor
• 5- kill
• 6- kill

Also, make sure to buy all the defense upgrades before the last event in day 7. You have enough money just by doing the run normally.