What is asymptomatic

Asymptomatic simply means there are no symptoms or without any symptoms of disease. An illness or condition that is present without any recognizable symptoms is regarded as an asymptomatic condition. For example, many people have high blood pressure, diabetes, high cholesterol, kidney disease, heart disease and aneurysms, have no symptoms. Furthermore, some cancers like ovarian cancer, breast cancer, pancreatic cancer, skin cancers, colon cancer, prostate cancer and lung cancer may produce little or no symptom until the cancers are well advanced. Even some infections may produce no symptoms early on such as asymptomatic bacteriuria, sexually transmitted infections (STIs) (e.g., chlamydia, gonorrhoea), worms infection, parasites infection, herpes infection, malaria, Ebola virus infection ¹, Zika virus infection ² and many more.

You are considered asymptomatic if you:

• Have recovered from an illness or condition and no longer have symptoms
• Have an illness or condition (such as early stage high blood pressure or glaucoma) but do not have symptoms of it

Asymptomatic bacteriuria

Most of the time, your urine is sterile. This means there is no bacteria growing. On the other hand, if you have symptoms of a bladder or kidney infection, bacteria will be present and growing in your urine.

Sometimes, your health care provider may check your urine for bacteria even when you do not have any symptoms. If enough bacteria are found in your urine, you have asymptomatic bacteriuria. Asymptomatic bacteriuria is defined as a quantitative count of > 100 × 10⁶ colony-forming units of bacteria per liter (CFU/L) of urine without specific symptoms of a urinary tract infection ³.

Asymptomatic bacteriuria is common, with varying prevalence by age, sex, sexual activity, and the presence of genitourinary abnormalities (Table 1). In healthy women, the prevalence of bacteriuria increases with age, from about 1 percent in females five to 14 years of age to more than 20 percent in women at least 80 years of age living in the community ⁴. Escherichia coli is the most common organism isolated from patients with asymptomatic bacteriuria. Infecting organisms are diverse and include Enterobacteriaceae, Pseudomonas aeruginosa, Enterococcus species, and group B streptococcus. Organisms isolated in patients with asymptomatic bacteriuria will be influenced by patient variables: healthy persons will likely haveE. coli, whereas a nursing home resident with a catheter is more likely to have multi-drug–resistant polymicrobic flora (e.g., Pseudomonas aeruginosa). Enterococcus species and gram-negative bacilli are common in men ⁵.

Table 1. Prevalence of Asymptomatic Bacteriuria in Selected Populations

Population		Prevalence (%)
Healthy premenopausal women		1.0 to 5.0
Pregnant women		1.9 to 9.5
Postmenopausal women (50 to 70 years of age)		2.8 to 8.6
Patients with diabetes
	Women	9.0 to 27.0
	Men	0.7 to 1.0
Older community-dwelling patients
	Women (older than 70 years)	> 15.0
	Men	3.6 to 19.0
Older long-term care residents
	Women	25.0 to 50.0
	Men	15.0 to 40.0
Patients with spinal cord injuries
	Intermittent catheter	23.0 to 89.0
	Sphincterotomy and condom catheter	57.0
Patients undergoing hemodialysis		28.0
Patients with an indwelling catheter
	Short-term	9.0 to 23.0
	Long-term	100

[Source ⁶ ]

Asymptomatic bacteriuria causes

Asymptomatic bacteriuria occurs in a small number of healthy people. It affects women more often than men. The reasons for the lack of symptoms are not well understood.

You are more likely to have asymptomatic bacteriuria if you:

• Have a urinary catheter in place
• Are female
• Are pregnant
• Are sexually active (in females)
• Have long-term diabetes and are female
• Are older adults
• Have recently had a surgical procedure in your urinary tract

Asymptomatic bacteriuria symptoms

There are no symptoms of this problem.

If you have these symptoms, you may have a urinary tract infection but you DO NOT have asymptomatic bacteriuria.

• Burning during urination
• Increased urgency to urinate
• Increased frequency of urination

Asymptomatic bacteriuria diagnosis

To diagnose asymptomatic bacteriuria, a urine sample must be sent for a urine culture. Most people with no urinary tract symptoms do not need this test.

You may need a urine culture done as a screening test even without symptoms if:

• You are pregnant
• You have a surgery or procedure planned that involves bladder, prostate, or other parts of the urinary tract

To make the diagnosis of asymptomatic bacteriuria, the culture must show a large growth of bacteria.

• In men, only one culture needs to show growth of bacteria
• In women, two different cultures must show growth of bacteria

The presence of a significant quantity of bacteria in a urine specimen properly collected from a person without symptoms or signs of a UTI (urinary tract infection) characterizes asymptomatic bacteriuria ⁷. Quantitative criteria for identifying significant bacteriuria in an asymptomatic person are: (1) at least 100,000 colony-forming units (CFUs) per mL of urine in a voided midstream clean-catch specimen; and (2) at least 100 colony-forming units (CFUs) per mL of urine from a catheterized specimen ⁸ (Table 2). According to the Infectious Diseases Society of America guideline, the diagnosis of asymptomatic bacteriuria in women is appropriate only if the same species is present in quantities of at least 100,000 colony-forming units (CFUs) per mL of urine in at least two consecutive voided specimens ⁹.

The leukocyte esterase and nitrite tests often are used in primary care settings to evaluate urinary symptoms; however, they are not useful for diagnosing UTI (urinary tract infection) in an asymptomatic patient. A urine dipstick leukocyte esterase test showing trace or more white blood cells has a sensitivity of 75 to 96 percent and specificity of 94 to 98 percent for detecting pyuria ¹⁰; however, pyuria is not specific for UTI (urinary tract infection) and may occur with other inflammatory disorders of the genitourinary tract (e.g., vaginitis). Urinalysis with microscopic examination for bacteria remains a useful test for the identification of bacteriuria.

Limitations of the dipstick nitrite test in diagnosing bacteriuria include: infection with non-nitrite–producing pathogens; delays between obtaining and testing the sample; and insufficient time since the last void for nitrites to appear at detectable levels. Combining the leukocyte esterase and nitrite tests results in higher specificity than using either test alone.

Table 2. Diagnostic Criteria for Asymptomatic Bacteriuria

Midstream clean-catch urine specimen:

For women, two consecutive specimens with isolation of the same species in quantitative counts of at least 100,000 colony-forming units (CFUs) per mL of urine.

For men, a single specimen with one bacterial species isolated in a quantitative count of at least 100,000 colony-forming units (CFUs) per mL.

Catheterized urine specimen:

In women or men, a single specimen with one bacterial species isolated in a quantitative count of at least 100 colony-forming units (CFUs) per mL.

[Source ⁶ ]

Asymptomatic bacteriuria treatment

Most people who have bacteria growing in their urine, but no symptoms, do not need treatment. This is because the bacteria are not causing any harm. In fact, treating most people with this problem may make it harder to treat infections in the future.

Premenopausal, nonpregnant women with asymptomatic bacteriuria experience no adverse effects and usually will clear their bacteriuria spontaneously ⁶. However, these women are more likely to experience subsequent symptomatic UTI (urinary tract infection) than women who do not have asymptomatic bacteriuria ¹¹. One study randomized women with bacteriuria to receive one week of nitrofurantoin (Furadantin) or placebo; those receiving the antibiotic had a significantly lower prevalence of bacteriuria at six months, but not at one year ¹². The patients treated with antibiotics were just as likely as those in the placebo arm to have a symptomatic UTI (urinary tract infection) in the year after therapy. Although women with asymptomatic bacteriuria are more likely to have subsequent symptomatic UTIs (urinary tract infections), treatment of asymptomatic bacteriuria does not decrease the frequency of symptomatic UTI (urinary tract infection) or prevent further episodes of bacteriuria. Asymptomatic bacteriuria has not been shown to be associated with detrimental long-term outcomes (e.g., hypertension, renal failure, genitourinary cancer, or decreased survival). For these reasons, the Infectious Diseases Society of America does not recommend screening for or treatment of asymptomatic bacteriuria in premenopausal nonpregnant women ⁹.

However, for some people getting a urinary tract infection is more likely or may cause more severe problems. As a result, treatment with antibiotics may be needed if:

• You are pregnant.
• You had a kidney transplant recently.
• You are scheduled for surgery involving the prostate gland, the bladder and those with infected kidney stones.
• Young children with vesico-ureteric reflux (backward movement of urine from the bladder into ureters or kidneys).

Without symptoms being present, even those who are older adults, have diabetes, or have a catheter in place, do not need treatment.

Women with Diabetes

Studies of women with diabetes show no difference between initially asymptomatic bacteriuric and nonbacteriuric women in the incidence of UTI, mortality, or progression to diabetic complications at 18 months ¹³ or 14 years ¹⁴. In a study of antibiotic therapy versus no therapy for women with diabetes and asymptomatic bacteriuria, antimicrobial therapy did not delay or decrease the frequency of symptomatic UTI or the rate of hospitalization for UTI or other causes at up to three years’ follow-up ¹⁵. These studies support the Infectious Diseases Society of America guidelines ⁹ that screening for or treatment of asymptomatic bacteriuria in women with diabetes is not indicated.

Older Patients with Asymptomatic Bacteriuria

Studies of asymptomatic bacteriuria in pre- and postmenopausal women report similar outcomes regardless of age ¹⁶. A study of ambulatory women in a long-term care facility who were assigned to receive antimicrobial therapy or placebo for bacteriuria showed a decrease in prevalence of asymptomatic bacteriuria at six months among those receiving antibiotics, but no significant difference in symptomatic episodes ¹⁷. Adverse outcomes attributable to asymptomatic bacteriuria were not observed in a cohort of ambulatory male veterans older than 65 years at several years’ follow-up ⁵.

Clinical trials of older residents in long-term care facilities have shown no benefits from screening for or antimicrobial treatment of asymptomatic bacteriuria ¹⁸. Although antimicrobial treatment does not decrease symptomatic infection or improve survival, there is an increased incidence of adverse antimicrobial effects and reinfection with antibiotic-resistant organisms. Thus, the Infectious Diseases Society of America does not recommend screening for or treatment of asymptomatic bacteriuria in older patients ⁹.

Patients with Spinal Cord Injuries

Patients with spinal cord injuries have a higher prevalence of asymptomatic bacteriuria and symptomatic UTI ¹⁹. Patients with spinal cord injuries and with asymptomatic bacteriuria treated using antibiotics uniformly showed early recurrence of bacteriuria following therapy. When treated with seven to 14 days of antibiotics, 93 percent of patients were again bacteriuric by 30 days ²⁰. Posttreatment urine cultures showed increased antimicrobial resistance as well. A prospective, randomized trial in patients with asymptomatic bacteriuria and intermittent catheterization showed similar rates of UTI at follow-up, whether or not prophylactic antimicrobials were administered ²¹. Although there are few trials addressing the treatment of asymptomatic bacteriuria in patients with spinal cord injuries, review articles and consensus guidelines support the Infectious Diseases Society of America recommendations ⁹ that asymptomatic bacteriuria should not be screened for or treated in patients with spinal cord injuries.

Patients with Indwelling Urethral Catheters

Patients with chronic indwelling Foley catheters are uniformly bacteriuric, but treatment is warranted only if the patient is symptomatic. Urine that is cloudy or foul-smelling often prompts a call from a long-term care facility to the physician, with an expectation that an evaluation, if not antibiotic therapy, will be ordered. However, in the asymptomatic patient, cloudy or foul smelling urine is not an indication for urinalysis, culture, or antimicrobial treatment ⁶. A study of residents in long-term care facilities with chronic indwelling catheters and bacteriuria who were treated with cephalexin (Keflex) or no therapy showed no differences in the incidence of fever or reinfection; however, patients who received antibiotic therapy had twice the incidence of subsequent microbial resistance to cephalexin ²².

When possible, the indwelling catheter should be removed, and the patient should receive clean intermittent catheterization to reduce the risk of symptomatic UTI. The replacement of a chronic indwelling Foley catheter is associated with a low risk for bacteremia, and antimicrobial treatment or prophylaxis is not indicated for this procedure ²³. A study in young women with short-term catheterization reported increased symptomatic infection over two weeks following catheter removal, when asymptomatic bacteriuria persisted 48 hours after the removal of the indwelling catheter ²⁴. Accordingly, the Infectious Diseases Society of America recommends that asymptomatic bacteriuria should not be screened for or treated in patients with an indwelling urethral catheter, but that treatment of women with persistent catheter-acquired bacteriuria at least 48 hours after catheter removal may be considered ⁹.

Asymptomatic bacteriuria possible complications

If it is not treated, you may have a kidney infection if you are at high risk.

Asymptomatic bacteriuria in pregnancy

Women with diabetes, recurrent urinary tract infections, polycystic kidneys, other congenital renal anomalies and sickle cell disease are at higher risk for asymptomatic bacteriuria and associated complications in pregnancy ²⁵. Prevalence of asymptomatic bacteriuria has been estimated to be 2%–10% in pre-menopausal ambulatory women ²⁶.

Women with asymptomatic bacteriuria during pregnancy are more likely to deliver premature or low-birth-weight infants and have a 20- to 30-fold increased risk of developing pyelonephritis during pregnancy compared with women without bacteriuria ¹². A Cochrane systematic review ²⁷ found that studies have consistently reported that treatment of asymptomatic bacteriuria in pregnancy decreases the risk of subsequent pyelonephritis from a range of 20 to 35 percent to a range of 1 to 4 percent. Antimicrobial treatment of asymptomatic bacteriuria also improves fetal outcomes, with decreases in the frequency of low-birth-weight infants and preterm delivery ²⁸. Early studies usually continued antimicrobial therapy for the duration of pregnancy; however, more recent studies reported similar benefits in patients treated for 14 days with nitrofurantoin or trimethoprim/sulfamethoxazole (Bactrim, Septra) compared with those treated with continuous antimicrobial therapy to the end of pregnancy ²⁹. The Infectious Diseases Society of America recommends a course of three to seven days of antimicrobial therapy for pregnant women with asymptomatic bacteriuria ⁹. A Cochrane systematic review found insufficient evidence to determine whether a single dose regimen is as effective as treatments of longer duration ³⁰.

Because leukocyte esterase and nitrite tests have low sensitivity for identifying bacteriuria in women who are pregnant, these patients should be screened with urine cultures ³¹; however, the optimal frequency of urine culture screening has not been established. A single urine culture at the end of the first trimester generally is recommended based on clinical outcomes and cost-effectiveness ³². Women with asymptomatic bacteriuria or symptomatic UTI during pregnancy should be treated (Table 3) and should undergo periodic screening for the duration of their pregnancy. The Infectious Diseases Society of America makes no recommendations for subsequent screening of pregnant women found to have no asymptomatic bacteriuria at the initial screen ⁹.

Table 3. National and international recommendations on screening for asymptomatic bacteriuria in pregnancy

Guideline group	Recommendation
Canadian Task Force on Preventive Health Care (current guideline, 2018)	We recommend screening pregnant women once during the first trimester with urine culture for asymptomatic bacteriuria (weak recommendation; very low-quality evidence). This recommendation applies to pregnant women who are not experiencing symptoms of a urinary tract infection and are not at increased risk for asymptomatic bacteriuria.
Canadian Task Force on the Periodic Health Examination33	Good evidence to include screening once by culture method for asymptomatic bacteriuria at 12–16 weeks of pregnancy.
United States Preventive Services Task Force34	The United States Preventive Services Task Force recommends screening for asymptomatic bacteriuria with urine culture for pregnant women at 12 to 16 weeks’ gestation or at their first prenatal visit, if later. (Grade A: The United States Preventive Services Task Force recommends the service. There is high certainty that the net benefit is substantial.)
Scottish Intercollegiate Guidelines Network, Scotland35	Standard quantitative urine culture should be performed routinely at first antenatal visit (Grade A). Confirm the presence of bacteriuria in the urine with a second urine culture (Grade A). Do not use dipstick testing to screen for bacterial urinary tract infection at the first or subsequent visits (Grade A). Treat asymptomatic bacteriuria detected during pregnancy with an antibiotic (Grade A). Women with bacteriuria that is confirmed by a second urine culture should be treated and have repeat urine culture at each antenatal visit until delivery (Grade C).
The National Institute for Health and Care Excellence, UK36	Women should be offered routine screening for asymptomatic bacteriuria by midstream urine culture early in pregnancy. Identification and treatment of asymptomatic bacteriuria reduce the risk of pyelonephritis.
The American Academy of Family Physicians37	Pregnant women should be screened for asymptomatic bacteriuria in the first trimester of pregnancy (Grade A: consistent, good-quality patient-oriented evidence). Pregnant women who have asymptomatic bacteriuria should be treated with antimicrobial therapy for 3 to 7 days (Grade B: inconsistent or limited-quality patient-oriented evidence).
The Infectious Disease Society of America 38	The diagnosis of asymptomatic bacteriuria should be based on results of culture of a urine specimen collected in a manner that minimizes contamination (Grade A-II). 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 (Grade A-I). Periodic screening for recurrent bacteriuria should be undertaken after therapy (Grade A-III). No recommendation can be made for or against repeated screening of women who are culture negative in later pregnancy.

[Source ³ ]

Asymptomatic bacteriuria in pregnancy treatment

Table 4. Oral Antibiotics for Treatment of Pregnant Women with Asymptomatic Bacteriuria

U.S. Food and Drug Administration (FDA) Pregnancy Category B: Safety for use in pregnancy has not been established

Amoxicillin

Amoxicillin/clavulanate (Augmentin)

Ampicillin

Cefuroxime (Ceftin)

Cephalexin (Keflex)

Nitrofurantoin (Furadantin)

Pregnancy Category C: No adequate well-controlled studies have been performed in women; should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus

Ciprofloxacin (Cipro)

Gatifloxacin (Tequin)

Levofloxacin (Levaquin)

Norfloxacin (Noroxin)

Trimethoprim/sulfamethoxazole (Bactrim, Septra)

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