Intra Abdominal Sepsis

Can anybody explain what is intra abdominal sepsis? A person that was closed to me died bcoz of it. And how we can trace it?  He was having a bad fever and pain in the stomach. But he could drive, walk and do many things like he was not having a serious disease. Only 6hours before he died, his condition getting worst.his BP getting down and so do his heart beat. 2  hours later, he thrown out blood. and the doctor could not do anything to safe him bcoz we sent him too late to hospital. i really need to nou bcoz I want to b aware in the future. So that I can take early action.