Elderly people with serious UTIs may not exhibit the hallmark sign of fever because their immune system is unable to mount a response to the infection. In fact, elders often don't exhibit any of the common symptoms listed above – or don't express them to their caregivers.
UTIs in the elderly are often mistaken for the early stages of dementia or Alzheimer's, according to National Institutes of Health (NIH), because symptoms include:
Confusion or delirium-like state
Agitation
Hallucinations
https://www.agingcare.com/articles/urinary-tract-infections-elderly-146026.htm