An 80-year-old woman residing in a nursing home develops confusion, urinary frequency, and urgency over 2 days. She has a long-term indwelling urinary catheter. A urine dipstick is positive for nitrites and leukocytes. Her temperature is 37.6°C, other observations are stable. She has no flank pain or signs of systemic sepsis. According to NICE guidelines, what is the most appropriate management?