Urine is normally sterile. Asymptomatic bacteriuria is a condition in which a significant number of bacteria appear in the urine, without the presence of typical symptoms of a urinary tract infection. Presence of >10 leukocytes/mm³ is considered as pyuria but not asymptomatic bacteriuria unless the number exceeds ≥10⁵ colony forming units(cfu)/mL. There are two main pathogenesis that might be responsible for asymptomatic bacteriuria which include microbial virulence and host factors. Escherichia coli is the single most common cause of asymptomatic bacteriuria. Asymptomatic bacteriuria is more common in elderly and its prevalence increase with age. Asymptomatic bacteriuria has been slightly more common in black population. Asymptomatic bacteriuria has risk factors similar to symptomatic bacteriuria such as pregnancy, aging, diabetes mellitus, sexual intercourse, using diaphragm plus spermicide, BPH, renal stones, or patients with spinal cord injuries, hemodialysis, indwelling urethral catheters, genitourinary abnormalities. Screening for asymptomatic subjects is considered if bacteriuria is associated with preventable adverse outcomes such as symptomatic urinary infection, progression to chronic kidney disease or hypertension, development of urinary tract cancer, and decreased duration of survival. If left untreated asymptomatic bacteriuria normally cures on its own and active treatment is not required except in those who are pregnant, require renal transplantation or are supposed to undergo a urinary tract procedure. In patients who acquire asymptomatic bacteriuria early in their pregnancy, there is a minute chance of issues related to pregnancy like low birth weight etc or pyelonephritis. Most cases resolve postpartum. The diagnosis of bacteriuria in an asymptomatic individual is based on the culture results of urine collected in a manner that minimizes the possibility of contamination and limits the period between sampling and testing the specimen to avoid false positivity due to bacterial growth. Treatment is not required in otherwise healthy individuals unless it is associated with a urinary tract infection. Conditions that might require the asymptomatic bacteriuria to be treated are pregnancy, before transurethral prostatic resection, and renal transplant follow-up.

• In 1950s, Kass et al. proposed a quantitative culture method for the microbiological diagnosis of urinary tract infections.^[1]
• About 10⁵ bacteria per milliliter must be present in the urine specimen to be consistently read as positive, which is seen in 95% of samples from patients with pyelonephritis.^[2][3]

According to the Infectious Disease Society of America (IDSA), asymptomatic bacteriuria is defined as the presence of ≥10⁵ cfu/mL of bacteria in clean catch urine specimen of an asymptomatic person with respect to symptoms urinary tract infection. By definition, one positive sample is enough to confirm asymptomatic bacteriuria in men, whereas in women two consecutive samples with same organism are required to diagnose asymptomatic bacteriuria. In men or women who are catheterized and are asymptomatic, identification of ≥10² cfu/mL of a single organism in the catheterized specimen is defined as asymptomatic bacteriuria. The prevalence of bacteriuria is more in sexually active women (4.6%) as compared to sexually inactive women (0.7%) or men.

• There are two main pathogenesis that might be responsible for asymptomatic bacteriuria which include microbial virulence and host factors.

• Symptomatic urinary tract infections require attachment, multiplication, and spread of bacteria in the urinary tract. Fimbriae are very helpful in attachment of the bacteria inside the urinary tract. It has been discovered that the pathogenic strains that have a decreased ability of making fimbriae, have a greater ability to multiply and thus are responsible for causing asymptomatic bacteriuria.^[4]

• Asymptomatic bacteriuria may also be due to the decreased virulence of some strains that gather in the bladder but do not cause a symptomatic appearance. Some strains isolated from patients with asymptomatic bacteriuria in the setting of spinal cord injury have decreased capability of causing hemolysis.^[5][6]

• Another possibility is the defective host response. A decreased expression of Toll-like receptor (TLR) 4 on the neutrophils in children with asymptomatic bacteriuria predisposes them to asymptomatic bacteriuria.^[7][8]

• Escherichia coli is the single most common cause of asymptomatic bacteriuria.^{[9][10][11][12]}
• Other causes of asymptomatic bacteriuria include:

Asymptomatic Bacteriuria must be differentiated from other diseases that might cause bacteriuria.^{[28][29][30][31]}

To review differential diagnosis of pyuria, click here.

To review differential diagnosis of sterile pyuria, click here.

• The prevalence of bacteriuria is more in sexually active women (4.6%) as compared to sexually inactive women (0.7%).^[40]
• Asymptomatic bacteriuria has a prevalence of 8-14% in diabetic women.^[41]

• Asymptomatic bacteriuria is more common in elderly and its prevalence increase with age.^[42][43]
• The prevalence of asymptomatic bacteriuria in women greater than 80 years old is >20%.^[44][45]
• The prevalence of asymptomatic bacteriuria in men greater than 75 year old is 6-15%.^[46]
• Asymptomatic bacteriuria is present in 3-5% of the women population between 38-60 years of age. It was identified in 5% of women in universities and 6% of women in groups related to health maintenance organisations.^[47][48]

• Asymptomatic bacteriuria is more prevalent in females as compared to males.
• Asymptomatic bacteriuria is rare among healthy men.^[49][50]

• Asymptomatic bacteriuria has been slightly more common in black population.^[51]

Asymptomatic bacteriuria has risk factors similar to symptomatic bacteriuria. Some of these include:^[52][53]

• Sexual intercourse
• Use of diaphragm plus spermicide

• BPH
• Renal stones
• Pregnancy^[54]
• Elderly
• Diabetes mellitus^[55]
• Patients with spinal cord injuries^[56][57]
• Patients undergoing hemodialysis^[58]
• Patients with indwelling urethral catheters^[59]
• Patients with genitourinary abnormalities^[59][60]

Screening for asymptomatic subjects is considered if bacteriuria is associated with preventable adverse outcomes such as symptomatic urinary infection, progression to chronic kidney disease or hypertension, development of urinary tract cancer, and decreased duration of survival.^[61]

The following should be screened for asymptomatic bacteriuria:^[62][63]

• Pregnant
• Requiring urologic procedures like transurethral resection of the prostate (TURP)
• Post renal transplant

It is not recommended to screen for or treat asymptomatic bacteriuria or fungiuria for short or long term catheters, exceptions are catheterized pregnant women and women with persistent bacteriuria 48 hours after removal of the urethral catheter. Prophylaxis can also be used also with patients undergoing urological procedures.^[64][65]

• No benefit of therapy of asymptomatic bacteriuria due to similar recurrence rates with more resistance to antibiotics.^[66][67]
• Significant improvement has been shown with women treated for bacteriuria that existed 48 hours after removal of indwelling urethral catheters.^[68]

• If left untreated asymptomatic bacteriuria normally cures on its own and active treatment is not required except in those who are pregnant, require renal transplantation or are supposed to undergo a urinary tract procedure. Asymptomatic bacteriuria should also be treated in the presence of a structural defect of the urinary tract.^[63]
• In patients who acquire asymptomatic bacteriuria early in their pregnancy, there is a minute chance of issues related to pregnancy like low birth weight etc or pyelonephritis. Most cases resolve postpartum.^[69]

Asymptomatic bacteriuria rarely leads to complications. These may include:

• Symptomatic UTI^[70]
• Complications in pregnancy such as:
  • Preterm birth^[71]
  • Low birth weight^[72][73]
  • Pyelonephritis later in pregnancy^[74]

Asymptomatic bacteriuria has a good prognosis and completely resolves with treatment.^[75]

The diagnosis of bacteriuria in an asymptomatic individual is based on the culture results of urine collected in a manner that minimizes the possibility of contamination and limits the period between sampling and testing the specimen to avoid false positivity due to bacterial growth.

The quantitative definition for significant bacteriuria is:^[76]

• For asymptomatic women, bacteriuria is defined as 2 consecutive voided urine specimens with isolation of the same bacterial strain in quantitative counts of ≥10⁵ CFU/mL.

• A single, clean-catch, voided urine specimen with 1 bacterial species isolated in a quantitative count of ≥10⁵ CFU/mL identifies bacteriuria in asymptomatic men.

• A single catheterized urine specimen with 1 bacterial species isolated in a quantitative count of ≥10² CFU/mL identifies bacteriuria in women or men.

Patients with asymptomatic bacteriuria are asymptomatic.

Patients with asymptomatic bacteriuria appear completely normal.

• Urinalysis
  • Urinalysis along with microscopic examination of the sample is useful in identifying bacteriuria.
  • Pyuria can also be identified on urinalysis.^[77]
  • Pyuria is defined as increased numbers of polymorphonuclear leukocytes in the urine and is evidence of an inflammatory response in the urinary tract.^[78] An operational definition of pyuria is the presence of ≥10 leukocytes per 400x microscopic field in the sediment of first-void urine. Although pyuria is prevalent among people with asymptomatic bacteriuria, its presence or degree has not been shown to correlate with the prognosis and should not affect clinical decisions about antibiotics.^{[79][80][81][56][82][83][84][85]}
• Urine culture
  • Urine culture is done to confirm the presence of the causative bacterial species and to see if it meets the criteria for asymptomatic bacteriuria i.e ≥10⁵ CFU/mL.^[86]

There are no ECG findings associated with asymptomatic bacteriuria.

There are no x-ray findings associated with asymptomatic bacteriuria.

There are no echocardiography/ultrasound findings associated with asymptomatic bacteriuria.

There are no CT scan findings associated with asymptomatic bacteriuria.

There are no MRI findings associated with asymptomatic bacteriuria.

There are no other imaging findings associated with asymptomatic bacteriuria.

There are no other diagnostic studies associated with asymptomatic bacteriuria.

Treatment is not required in otherwise healthy individuals unless it is associated with a urinary tract infection. Some other conditions that might require the asymptomatic bacteriuria to be treated are:^{[87][88][89][63][90][91]}

• Pregnancy
• Requiring urinary tract procedure e.g transurethral prostatic resection
• Renal transplant follow-up

• 1. Empiric antimicrobial therapy

• Treatment of asymptomatic bacteriuria is not recommended for the following persons:

• Premenopausal, nonpregnant women
• Diabetic women
• Older persons residing in the community
• Elderly, institutionalized subjects
• Persons with spinal cord injury
• Catheterized patients while the catheter remains in situ
• Note (1): Pyuria accompanying asymptomatic bacteriuria is not indicated for antibiotic therapy.

• 2. Specific considerations

• 2.1 Women, pregnant

• Preferred regimen (1): Nitrofurantoin 100 mg PO bid for 3–5 days (avoid in glucose-6-phosphate dehydrogenase deficiency)^[92]
• Preferred regimen (2): Amoxicillin 500 mg PO tid for 3–5 days
• Preferred regimen (3): Amoxicillin-Clavulanate 500 mg PO bid for 3–5 days
• Preferred regimen (4): Cephalexin 500 mg PO tid for 3–5 days
• Preferred regimen (5): Fosfomycin 3 g PO single dose
• Preferred regimen (6): Trimethoprim 200 mg PO bid for 3–5 days (only after first trimester)
• Note (1): Pregnant women should be screened for bacteriuria by urine culture at least once in early pregnancy, and they should be treated if the results are positive.
• Note (2): Periodic screening for recurrent bacteriuria should be undertaken after therapy.
• Note (3): Infectious Disease Society of America (IDSA) guidelines recommend 3–7 days of antibiotic therapy.

• 2.2 Patients with indwelling urethral catheters

• Screening for or treatment of asymptomatic bacteriuria in patients with indwelling urethral catheters is not recommended.
• Note (1): Antimicrobial treatment of asymptomatic women with catheter-acquired bacteriuria that persists 48 hours after catheter removal may be considered.

• 2.3 Urologic interventions

• Screening for or treatment of asymptomatic bacteriuria before transurethral resection of the prostate is recommended.^[93]
• Preferred regimen (1): Trimethoprim-Sulfamethoxazole DS 1 tab PO bid for 3 days after obtaining urine culture

• 2.4 Renal transplant

• Screening for or treatment of asymptomatic bacteriuria after a renal transplant is recommended.^[94][95][96]

• 2.5 Catheter Associated Asymptomatic Bacteriuria

• Preferred regimen (1): Trimethoprim-Sulfamethoxazole DS 1 tab PO bid for 3 days

• A large proportion of women with asymptomatic bacteriuria in pregnancy have a recurrence after a short duration of therapy and for this reason a followup is done one week after completing the therapy and then monthly until the birth due to a higher chance of recurrence.^[97]

Surgical intervention is not recommended for the management of asymptomatic bacteriuria.

Primary preventive measure for asymptomatic bacteriuria include:^[98][99]

• Proper glycemic control
• Safe sexual practice
• Adequate hydration

Secondary preventive measures for asymptomatic bacteriuria include:

• Prophylactic antibiotics