Severe Short Term Memory Loss, Weakness, Fever, Incontinence, Normal Scan Results, High WBC, Advised Lumbar Spine MRI. Suggestions?

Hi - My dad (75 yrs old) was admitted to the hospital with severe short term memory loss , extreme weakness, fever and has since become incontinent. Scans of his brain, heart, lungs and sonograms of his legs have all come back normal. His white blood cell count is high. There is no evidence of a bacterial infection . The doctors haven t been able to come up with anything. Most recently, the neurologist ordered an MRI of his lumbar spine . Any guesses what we should be looking for? Two years ago he was admitted with much more severe neurological symptoms - completely irrational behavior, confusion, which the doctors eventually attributed to a URI, which didn t seem right to us, but eventually he recovered. They also said he had a heart attack at some point, which led to a sextuple bypass a few months later. The surgery went fine, but he had difficulty immediately afterwards. He didn t come out of the anesthesia well and was again, confused and irrational. Eventually he recovered and the doctors blamed ICU psychosis. My family believes there s an underlying problem that they re not identifying, but we don t know what to ask or what to look for. Can you make any suggestions? Thanks.