What Causes High Fever And Swollen Legs After Treating Pericardial Effusion?

My 80 year old father in law fell ill a week and a half ago. He suddenly felt ill, vomited and then developed a 101 fever. He was not brought to the hospital for 36 hours later when he became lethargic and his fever spiked to over 102 degrees. While in the hospital they did numerous tests and determined that he had fluid around his heart. His legs swelled and he had issues with confusion and was very irritable. Over his week stay in the hospital, they brought his fever down, and did numerous tests. He was put on three different anit biotics to deal with a bacterial infection that they could not identify by the hospital (the CDC representative was perplexed and could not identify what was going on with him). He was released on Monday and is not improving. A week and a half ago, my father in law was a vibrant man designing and working on the new construction in his basement. Today, he can barely walk, is exhausted, has confusion, difficulty writing. At one point they thought it was blood poisoning, but that was later dismissed. We are perplexed and are hoping you could shed some light on his situation. Thank you.