Could it be a bacterial infection?

My husband had a large piece of his descending aorta replaced with dacron 5 months ago, and he also has a bicuspid aortic valve with swelling of 3.5 cm in his ascending aorta, which will be replaced at a later time. But lately he has had the chills, fever, weight loss, headaches, his skin color is pale, his eyes are sunk in, and he is breathless almost all of the time. He went to the Dr. and they are running some tests on him. I was just wondering if anyone had any ideas what it could be and if it could be related to his heart and or his sugery?