Asymptomatic bacteriuria (ASB) is a common condition, especially among patients with urinary catheters and older adults, and is often mistaken for a urinary tract infection (UTI). Patients with ASB have bacteria in the urine but no symptoms of infection. Treatment is rarely indicated and can cause harm. Proper diagnosis, clinician and patient education, and avoiding unnecessary antibiotics are central to appropriate management.

When we set up the Northwestern Medicine Complex Urologic Infections Interdisciplinary Clinic, I made the logical decision to tell the screeners that I only wanted to see patients with documented infections. However, many patients got through who had symptoms without documentation. Then I learned something very interesting: upon further study, some of these patients actually had ASB and not a UTI.

ASB is a lot more common than most people think, and it is not something that only occurs in a specific population. It is particularly common in patients with an indwelling urinary catheter because bacteria develop frequently with increasing duration of catheterization. Basically, the symptoms of ASB are anything other than dysuria, frequency, and urgency. Symptoms such as cloudy urine, foul-smelling urine, and changes in mental status are not sufficient to diagnose UTIs in the absence of other signs and symptoms of infection. Patients with ASB also will have bacteria in their urine. Although bacteria are there, you just have to explain to the patient that this is not an infection.

Patients who go to the emergency department with a fever often think that they must have a UTI. At our clinic at Northwestern, we make a concerted effort to educate the emergency department providers to not assume that such patients have UTIs without having a full picture. They need to rule out other potential sources of their symptoms or reasons for infection. When we finish a consultation for a UTI at our clinic, we often will call the referring physician and explain to them what we found. We have learned that, over time, these providers will become advocates for helping their patients and other providers understand ASB and its appropriate management, and we will see fewer referrals for patients with ASB.

Moreover, many older patients will eventually have ASB. Why is that? Could it be that ASB is actually a good thing, and instead of being just neutral, maybe having ASB is advantageous? To test this, we took ASB Escherichia coli strains and studied them in mouse models. We found out that these strains had 2 significant properties. First, they were analgesic, and, second, they were able to prevent or reduce the infection. The strains were antimicrobial for UTI in a mouse model. So, when discussing ASB with my patients, I sometimes will tell them that the ASB could have analgesic and antimicrobial activity, and therefore they should not worry about it being there.

ASB rarely requires treatment; however, an important scenario in which ASB should be treated is when a woman with ASB is pregnant. Also, if a patient is having a urologic procedure in which the urothelium is going to be cut, then we do use antibiotic prophylaxis before surgery. The most unfortunate complications of treating ASB unnecessarily are that patients can develop significant resistant bacteria and experience a lot of side effects.