Background: The diagnosis of urinary tract infections (UTIs) in institutionalized older adults is often based on vague

symptoms and a positive culture. The high prevalence of asymptomatic bacteriuria (ABU), which cannot be easily

discriminated from an acute infection in this population, is frequently neglected, leading to a vast over-prescription

of antibiotics. This study aimed to identify subpopulations predisposed to transient or long-term ABU.

Methods: Residents in a long-term care facility were screened for ABU. Mid-stream urine samples were collected

during two sampling rounds, separated by 10 weeks, each consisting of an initial and a confirmative follow-up

sample.

Results: ABU occurred in approximately 40% of the participants and was mostly caused by Escherichia coli. Long-term

ABU (> 3 months) was found in 30% of the subjects. The frailest women with urinary incontinence and dementia had

drastically increased rates of ABU and especially long-term ABU. ABU was best predicted by a scale describing the

functional independence of older adults.

Conclusions: Institutionalized women with incontinence have ABU prevalence rates of about 80% and are often

persistent carriers. Such prevalence rates should be considered in clinical decision making as they devalue the meaning

of a positive urine culture as a criterion to diagnose UTIs. Diagnostic strategies are urgently needed to avoid antibiotic

overuse and to identify patients at risk to develop upper UTI.