What is asymptomatic bacteriuria (ASB) and how is it diagnosed?

From the Guidelines

Asymptomatic bacteriuria is diagnosed when a urine culture shows significant bacterial growth (typically ≥100,000 colony-forming units per milliliter) in a properly collected urine specimen from a person who has no symptoms such as burning during urination, frequency, urgency, or pelvic pain. This condition is characterized by the presence of bacteria in the urine without any symptoms of urinary tract infection. The diagnosis of asymptomatic bacteriuria requires at least one properly collected urine specimen, though two consecutive positive samples are sometimes recommended for greater accuracy, especially in women [ 1 ].

Diagnosis Criteria

For asymptomatic women, bacteriuria is defined as 2 consecutive voided urine specimens with isolation of the same bacterial strain in quantitative counts ≥10^5 cfu/mL [ 1 ]. A single, clean-catch voided urine specimen with 1 bacterial species isolated in a quantitative count ≥10^5 cfu/mL identifies bacteriuria in men [ 1 ]. A single catheterized urine specimen with 1 bacterial species isolated in a quantitative count ≥10^2 cfu/mL identifies bacteriuria in women or men [ 1 ].

Treatment Recommendations

It's essential to note that asymptomatic bacteriuria generally doesn't require treatment except in pregnant women and patients undergoing urologic procedures [ 1 ]. In pregnant women, treatment typically involves antibiotics such as nitrofurantoin, amoxicillin-clavulanate, or cephalexin [ 1 ]. The U.S. Preventive Services Task Force also recommends screening for asymptomatic bacteriuria in pregnant women, as it can reduce the incidence of symptomatic maternal urinary tract infections and low birthweight [ 1 ].

Key Points

• Asymptomatic bacteriuria is a common condition that can be diagnosed with a urine culture.
• The condition generally doesn't require treatment except in pregnant women and patients undergoing urologic procedures.
• Screening for asymptomatic bacteriuria in pregnant women can reduce the incidence of symptomatic maternal urinary tract infections and low birthweight.
• The U.S. Preventive Services Task Force recommends against screening for asymptomatic bacteriuria in men and nonpregnant women, as the potential harms associated with overuse of antibiotics outweigh the benefits [ 1 ].

From the Research

Definition of Asymptomatic Bacteriuria

• Asymptomatic bacteriuria is a condition in which bacteria are present in a noncontaminated urine sample collected from a patient without signs or symptoms related to the urinary tract 2
• It is a common clinical condition that often leads to unnecessary treatment, with incidence increasing with age and more prominent in women than men 3
• Asymptomatic bacteriuria is seldom associated with adverse outcomes, and treatment is not beneficial for most individuals, except for selected groups such as pregnant women and those undergoing traumatic genitourinary interventions 4

Diagnosis of Asymptomatic Bacteriuria

• Urine culture is the gold standard for detection of urinary tract infection, including asymptomatic bacteriuria 5
• Dipstick urinalysis is popular for its availability and usefulness, but results must be interpreted in context of the patient's pretest probability based on symptoms and characteristics 5
• Microscopic urinalysis is likely comparable to dipstick urinalysis as a screening test, and bacteriuria is more specific and sensitive than pyuria for detecting urinary tract infection 5
• Screening for asymptomatic bacteriuria is recommended for pregnant women, individuals who are to undergo traumatic genitourinary interventions, and renal transplant recipients, but not for most other populations 4, 3

Management of Asymptomatic Bacteriuria

• Antibiotic treatment of asymptomatic bacteriuria has not been shown to improve patient outcomes, and unnecessary treatment is often associated with unwanted consequences such as increased antimicrobial resistance and health care cost 3
• The Infectious Disease Society of America (IDSA) updated its asymptomatic bacteriuria management guidelines in 2019, emphasizing the risks and benefits of treating the condition 3
• Treatment is recommended for pregnant women, individuals who are to undergo endoscopic urologic procedures, but not for individuals with diabetes, neutropenia, spinal cord injuries, indwelling urinary catheters, and so on 3