For all of those who weren't able to read it, here's a vague explanation.

They went upstairs to Dan and he started explaining that the parasite (can't remember it's name) is a parasite that usually gets into rats, and then makes them weak and then cats eat the rat and then the parasite lives happily inside the cat. So the government decided to see what would happen if something like that happens to humans, so they ordered scientists to make up a fake pharmapheutical company to make a parasite for humans and they made everyone have it by a ebola prevention checkup, but OP didn't get it because he moved in after the checkup so he doesn't have it. But then the government decided to make it more powerful and thing got out of control and the research team left, but leaved an secret exit to the sewers where from people can escape and requires a key Dan has. And then the government decided that people should be evacuated, but then they realised that is a bad idea and started shooting everyone they saw. And then they hear a crash and from the monitors see freaks coming in so Angelina and op decide to escape while Dan makes a distraction, and at the door of the sewer Angela felt himself transform into a freak and before she transferred she gave him a picture of her daughter Helena and told him to give it to her and the address of him is on the back and then she closed the sewer door and let op escape