Asymptomatic bacteriuria (ABU) is a common, frequent condition, with multifactorial reasons increasing the risk, especially in the elderly. Also, while it is not recommended to routinely screen or treat adult patients with ABU because there is no evidence of potential benefit, IDSA recommends screening and management of ABU in pregnancy to improve the outcome and prevent pyelonephritis in these patients. Here are the current guidelines for the screening and management of ABU in clinical practice.

Introduction

Asymptomatic bacteriuria (ABU) is the presence of bacteria in the urine of a person with no clinical features of urinary tract infection. The incidence increases with age; both males and females in the age group of 65-80 years have a 15% increased incidence of ABU and 40-50% incidence above the age of 80 years. It commonly affects females compared to males. It is a benign condition and most of the patients do not have any adverse effects due to ABU. Escherichia coli is the most common organism associated with ABU. The risk factors include the following: [1]

• Obstructive pathologies such as calculi, prostatic hypertrophy, cystocele, etc.
• Faecal soiling of the perineum
• Long-term urinary catheters
• Repeated instrumentation of the urinary tract

Diagnosis of the condition

The Infectious Diseases Society of America (IDSA) criteria for diagnosis of ABU are as follows: [1]

1. Midstream clean catch urine specimen: The urine collection should be done with all due aseptic precautions to prevent sample contamination.
   1. Women: Two consecutive specimens with isolation of the same bacteria strain with a count of >100,000 colony-forming units (CFUs)/ml of urine.
   2. Men: A single specimen with isolation of one bacteria strain with a count of >100,000 CFUs/ml of urine.
2. Catheterised specimen:
   1. Single sample with isolation of one bacteria strain with a count of >100,000 CFUs/ml of urine.

Screening for ABU

The recommendations for screening for ABU are given in table 1 below: [2]

Table 1: Criteria for screening for ABU

Pregnant women should be screened at 12 to 16 weeks of gestation with a mid-stream urine culture. If positive, it should be repeated in 7 days. If two consecutive cultures come positive, they should be treated with appropriate antibiotics according to susceptibility reports.

Pathogenesis of ABU

There are several factors in the elderly predisposing them to increased risk of ABU. The reduction in immune response in the elderly causes persistent bacterial colonisation, especially in diabetic patients. The incidence of associated pathologies such as neurogenic bladder with incontinence of urine, obstructive uropathy and reduced bladder mucosal defence function in the elderly predisposes them to increased bacterial growth in the urinary tract. In addition, a reduction in hormonal levels in the elderly results in a change in the urinary and genital pH which is conducive for bacterial growth. Glycosuria in diabetics also increases the risk of bacterial colonisation. It has also been reported that genetic predisposition to reduced immune responses can aggravate bacterial growth. [2]

Management of ABU

Since ABU is a common presentation in clinical practice, physicians are in a dilemma to decide which patients would require treatment. Also, antimicrobial resistance is increasing and is a concern to the treating physician. Efforts are underway to reduce the burden of antimicrobial resistance by using the antimicrobials only in patients who would benefit from it. Therefore, it is recommended to treat ABU only in patients with potential benefit.

ABU in elderly individuals, diabetics, with indwelling catheters or spinal cord injuries need not be treated since it does not improve the outcome. Also, there is an increased risk of adverse effects of the antimicrobial drugs and reinfection with antibiotic-resistant organisms in these patients. Hence, IDSA does not recommend routine treatment of ABU with antibiotics in these patients. [3]

Pregnant women with ABU should be treated as they have an increased incidence of premature or low birth babies and approximately 20 to 30 times more risk of developing pyelonephritis. Treatment of ABU reduces the risk of pyelonephritis from 20-35% to 1-4%. Better foetal outcomes, reduced risk of preterm delivery and low birth weight of the infants are seen with antimicrobial treatment of ABU in pregnancy. Therefore, IDSA recommends the treatment of ABU in pregnant women with antimicrobial drugs. [3]

The management recommendation for pregnant women is as follows:

• Nitrofurantoin 100 mg orally, 12 hourly for 5 to 7days (avoid use during the first trimester and at term)
• Amoxicillin 500 mg orally, 8 hourly.(OR) Amoxicillin + clavulanate 625 mg 8 hourly
• Cephalexin 500 mg orally, 6 hourly
• Fosfomycin 3 g orally as a single dose
• Trimethoprim-sulfamethoxazole 160/800 mg every 12 hourly

The duration of therapy should be 5 to 7 days. Follow up culture should be done 7 days after completion of therapy to confirm the sterilisation of urine.

• If repeat culture shows no growth, there is no indication for further testing for bacteriuria in the absence of symptoms suggestive of UTI
• If repeat culture is positive for bacterial growth (≥105 CFU/ml), repeat the course of antimicrobial as per susceptibility pattern