An infection in the blood- septicemia- is serious especially in someone who has other health issues and is older. It is good that it was caught and treated. I would think that a chest x-ray would rule out pneumonia. Pneumonia is common in older people especially those with dementia because again the sensory input from the body to the brain that controls the swallowing muscles is damaged. Aspiration pneumonia is common. The feeling of having to urinate frequently could be due the failure of the part of his brain that tells him when he has to go. With dementia the whole brain is failing, not just memory. He may not be getting the correct input from his body to his brain. I you haven't already done so, I would recommend learning as much as you can about how dementia affects the entire brain. I found lots of information on the Alzheimer's Association website and Teepa Snow's website. God bless you and your loved one.