Introduction
Bacteriuria is the presence of bacteria in the urine and can be classified as symptomatic or asymptomatic. A patient with asymptomatic bacteriuria is further defined as having colonization with 1 or more organisms in a urine specimen without symptoms or infection. Bacteriuria without symptoms is not an infection. An example would be a patient with a long-term Foley with no symptoms, but significant bacteriuria is usually present.
Symptomatic bacteriuria is associated with a urinary tract infection, usually caused by a single organism. Lower urinary tract infections (UTIs) include cystitis and prostatitis, and upper UTIs include pyelonephritis and pyonephrosis. Most UTIs are considered to be simple or uncomplicated because they occur in healthy, nonpregnant women. Complicated UTIs involve individuals with a condition or a more resistant pathogen, which increases the risk of treatment failure. Examples of conditions that would be classified as complicated UTIs include all urinary infections in men, urinary tract abnormalities or obstructions, immunocompromising conditions, or the presence of a urethral catheter or another device, such as a double-J stent, in the urinary tract.[1][2][3][4]
Etiology
There are multiple ways for the urinary tract to become colonized or infected with bacteria. Typical patients who often colonize the urine are those older than 65 years of age or who have one of the following: chronic indwelling urinary catheters, neurogenic bladders, or a urinary stoma. Postmenopausal women may be at higher risk for colonization due to a loss of acidic vaginal pH.
Some individuals can begin colonizing with bacteria within 48 hours of urinary catheter placement. Common bacteria and fungi colonizers include Escherichia coli, Enterococcus species, and Candida species. Colonized patients may be asymptomatic, but some patients will become symptomatic due to an infection that must be treated. Women are more likely than men to develop UTIs as a result of their anatomy. E coli is the most common pathogen associated with UTIs.[5][6][7][8]
Epidemiology
The occurrence of asymptomatic bacteriuria versus urinary tract infections varies among different patient populations. Younger, healthy individuals can have asymptomatic bacteriuria, but it is less common than in older adults. The Infectious Diseases Society of America found a prevalence of 1% to 5% in healthy, premenopausal women and 1.9% to 9.5% in pregnant women. Increasing age is a risk factor, but prevalence is typically higher in females and those living in a long-term care facility (with or without a catheter). Women and men aged at least 70 years were found to have prevalence rates of 10.8% to 16% and 3.6% to 19%, respectively. Long-term care residents also had an increased prevalence, with 25% to 50% among women residents and 15% to 40% among residents who are men. Long-term use of indwelling urinary catheters is also associated with a 100% prevalence of asymptomatic bacteriuria, compared with up to 23% in short-term use. Women with diabetes have also shown an increased prevalence rate when compared to men with diabetes, 9% to 27% versus 0.7% to 11%, respectively.
Regarding UTIs, women are more likely to develop them than men, although rates increase in men after age 50. Approximately 50% of women will develop at least one UTI within their lifetime, with 1 in 3 women having a UTI by the age of 24. In younger women, UTI recurrence is 25% within 6 months of the first occurrence. If pregnant women with asymptomatic bacteriuria are not treated, up to 40% will develop a UTI, but the actual incidence of UTIs in pregnancy is as low as 4%. UTIs are the second most common infection for all elderly individuals not in long-term care, accounting for 25% of all infections. Individuals with indwelling urinary catheters are at higher risk of developing UTIs. The most common nosocomial infection in hospitals and nursing homes is the catheter-associated urinary tract infection (CAUTI).
Pathophysiology
Women frequently develop UTIs due to the urethra being close to the vagina and rectum, which can lead to the unintentional introduction of fecal flora into the urinary tract. The bacteria ascend from the urethra to the bladder in cystitis. If bacteria ascend from the bladder through the ureters to the kidneys, pyelonephritis develops. Pyelonephritis can also result from seeding of the kidneys via the lymphatic system from bacteremia.
When men develop UTIs, including prostatitis, it is usually due to an obstruction such as a urinary stone or enlarged prostate. The insertion of a chronic indwelling urinary catheter is also a risk factor for UTIs. Organisms can be introduced into the urinary tract via a catheter, through a patient's fecal or skin contaminants, or through healthcare personnel contact. Urinary catheters can promote the growth of uropathogens by providing a site for adhesion and by disrupting normal host defenses.
History and Physical
Individuals with symptomatic bacteriuria from a lower UTI commonly present with frequency, urgency, dysuria, and suprapubic pain with a rapid onset over a 24-hour period. Older adult patients often present with mental status changes, although other reasons for confusion or delirium should be part of the differential diagnosis. There are also nonspecific symptoms that may occur, including fatigue, irritability, malaise, nausea, headache, abdominal discomfort, and back pain. For individuals presenting with an upper UTI, the symptoms mentioned above can still be present, along with fever and flank pain. Individuals with UTIs may present with cloudy, dark, bloody, or foul-smelling urine, but any one of these factors presented alone should not automatically determine a UTI diagnosis.
Evaluation
If an individual presents with urinary tract symptoms consistent with a UTI or if a patient presents with severe sepsis of unknown origin, then a UTI must be considered as part of the differential diagnosis. The urinalysis and urine culture are the most important laboratory findings used to determine whether an individual has a UTI. First, a urinalysis must be evaluated to determine whether urinary white blood cell and leukocyte esterase values are abnormally high, indicating pyuria and possible infection. Other abnormalities may be observed on urinalysis in an individual with a UTI, including a positive nitrite test.[6][9][10]
If the urinalysis is considered significant for a UTI in a symptomatic patient without other reasons for the abnormal findings (eg, an asymptomatic individual with chronic urinary catheter placement), then empiric antibiotic treatment should be initiated. Empiric treatment with a negative urinalysis can be appropriate if the patient is neutropenic and has a UTI, based on other factors, including a significant number of organisms on urine culture and signs and symptoms of infection. When a urinalysis is obtained through a voided specimen, it is considered contaminated if there are more than 20 squamous cells per high-power field, and the sample should be recollected before initiating antibiotic therapy to determine whether empiric therapy is truly indicated. If the urinalysis finds elevated white blood cells (more than 10) and leukocyte esterase (positive value), but the individual has a chronic indwelling catheter, additional consideration should be placed on ensuring the patient has clinical symptoms of a UTI before starting treatment. A chronic indwelling urinary catheter with bacteriuria may irritate the bladder wall, resulting in pyuria without an actual infection.
Once the urine culture results are available, it should be determined whether the colony-forming unit (CFU) per milliliter (mL) is significant for UTI or indicative of possible contamination. In voided specimens, greater than or equal to 100,000 CFU/mL is considered diagnostic for an individual with a positive urinalysis. There is greater controversy regarding the CFU/mL cut-off for specimens collected from a urinary catheter, so signs and symptoms should be an even more important factor in the diagnostic evaluation. Technically, individuals with more than 1000 CFU/mL in a catheter specimen can have a UTI. Since urine collected correctly from a catheter should contain fresh, uncontaminated urine, a lower threshold for CFU/mL is justified compared with voided specimens. If 3 or more organisms are identified in the cultured urine, the specimen is considered contaminated.
Imaging studies are not routinely indicated in cystitis or acute uncomplicated pyelonephritis, but can be helpful in certain scenarios. Individuals with persistent symptoms after 48 to 72 hours of appropriate antibiotic therapy should undergo evaluation of the upper urinary tract, as well as those patients with pyelonephritis who appear severely ill. Computed tomography (CT) without contrast is usually the imaging study of choice, but contrast is needed for renal perfusion studies. Since there are no clinical signs that can reliably differentiate simple acute pyelonephritis from a dangerous, obstructed pyonephrosis that requires urgent surgery, consider an imaging study if there is a history of kidney stones or clinical suspicion of a stone.
Treatment / Management
Adults determined to have asymptomatic bacteriuria should not typically be treated unless pregnant, undergoing a genitourinary procedure, or immunocompromised (eg, neutropenic, possibly renal transplant). Before initiating antibiotics in individuals with a known UTI, urinary catheter removal or exchange should occur if it was not completed before urine specimen collection. Multiple antibiotics are available for the treatment of UTIs. These include fluoroquinolones, sulfamethoxazole/trimethoprim, beta-lactams, and nitrofurantoin (the latter only indicated for cystitis).
Increasing bacterial resistance to commonly used oral antibiotics has heightened the need to carefully review culture susceptibility results. The resistance of commonly encountered UTI pathogens occurs not only in the inpatient setting but also in outpatients. E coli and Klebsiella species are now becoming resistant via extended-spectrum beta-lactamase (ESBL)- positive or AmpC-producing mechanisms. There are some exceptions, but these resistance mechanisms lead to in vivo clinical failures with all penicillins, cephalosporins, and monobactams. Carbapenems are typically the drug class of choice in these multidrug-resistant pathogens.
Local antibiogram data should be reviewed to determine the best empiric therapy options for UTIs. This requires determining the best option for organisms such as E Coli, Klebsiella species, and Proteus species. Preferably, the susceptibility of a given organism should be 80% to 90% or higher, based on recent local urine susceptibility data. Empiric therapy should also be determined by an individual's allergies and any recent urinary cultures, in case multidrug-resistant organisms need to be covered.
Once an individual's culture susceptibility results are known, therapy should be modified to ensure that an antibiotic with the narrowest spectrum that covers the organism(s) being treated is used, while still achieving appropriate penetration into the bladder and kidneys as necessary. If the patient also has a bloodstream infection due to the same organism as the UTI, a bactericidal antibiotic is preferred. It should have at least 90% oral bioavailability if an oral antibiotic is an appropriate option for both sites of infection. Any antibiotics requiring renal dosing should be evaluated based on the individual's creatinine clearance or estimated glomerular filtration rate. Once the antibiotic has been appropriately de-escalated, one additional step should be taken to ensure that antimicrobial stewardship practices are implemented.
Clinicians should ensure that the duration of therapy is sufficient to eradicate the pathogen(s) but not excessively long to cause adverse events or resistance. Patients with uncomplicated cystitis are typically treated for 3 to 7 days, depending on the antibiotic chosen. In uncomplicated pyelonephritis, therapy ranges from 5 to 14 days, depending on the antibiotic used. In complicated cystitis and pyelonephritis, treatment can last 7 to 14 days, depending on individual circumstances. Of note, additional studies continue to evaluate shorter courses of therapy for urinary infections.
Differential Diagnosis
The differential diagnosis for bacteriuria includes the following:
Acute pyelonephritis
Bladder cancer
Chlamydia (chlamydial genitourinary infections)
Cystitis nonbacterial
Emphysematous pyelonephritis
Emphysematous cystitis
Interstitial cystitis
Pelvic inflammatory disease
Prognosis
Some women with recurrent UTIs that have been treated for asymptomatic bacteriuria have been found to have higher rates of symptomatic UTIs and a higher prevalence of antibiotic-resistant bacteria. For most patients presenting with UTIs, the prognosis is good unless they develop severe sepsis. In severely septic individuals, choosing the best antibiotic based on local antibiogram susceptibilities, clinical history, and individual patient characteristics is vital to successful outcomes, as mortality risk increases with every hour without the correct antibiotic therapy. In addition, avoiding unnecessary treatment is also vital to successful outcomes.
Enhancing Healthcare Team Outcomes
The management of bacteriuria requires good clinical acumen. Clinicians, including nurse practitioners, should ensure that the therapy eradicates the organism while avoiding adverse reactions. There are myriad other issues to consider when assessing and treating a patient with a possible UTI.
Not every individual with a chronic catheter or older adult with confusion will have a UTI upon presentation to the emergency room or hospital. Healthcare professionals should be diligent in collecting a thorough history and physical before collecting urine specimens. If an individual has a catheter urine sample collected and a UTI is questionable, the clinician should determine if the sample was appropriately collected before initiating or completing a full course of therapy. Ideally, a chronic indwelling catheter should be removed or exchanged before collecting a urinalysis and urine culture, when possible. Proper management of bacteriuria and urinary tract infections is necessary for patient care and to minimize the spread of highly antibiotic-resistant organisms. Avoiding unnecessary treatment of asymptomatic bacteria (except in pregnancy) is a good first step.
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Disclosure: Marsha Crader declares no relevant financial relationships with ineligible companies.
Disclosure: Antoine Kharsa declares no relevant financial relationships with ineligible companies.
Disclosure: Stephen Leslie declares no relevant financial relationships with ineligible companies.
