18: Urinary Tract Infection

CHAPTER 18 Urinary Tract Infection


Urinary tract infections (UTIs) are one of the most common bacterial infections in human beings, accounting for more than 8 million patient visits per year.1 Acute UTIs are primarily a disease of young, sexually active women. Approximately one in three women will experience at least one diagnosed UTI necessitating antibiotic treatment by the age of 24 years, and 40% to 50% of women will experience at least one UTI during their lifetimes.2 The annual cost of health care services reaches $2 billion in the United States alone.3


UTIs have been traditionally classified according to the anatomic site of the infection. Examples of lower UTIs include cystitis, urethritis, and prostatitis; pyelonephritis and perinephric abscess are examples of upper UTIs. UTIs are also classified as complicated or noncomplicated. A noncomplicated UTI occurs in the absence of structural or neurologic abnormalities that would interfere with the normal flow of urine. A complicated infection may occur in either the upper or lower urinary tract but is accompanied by an underlying condition that increases the risk of a therapeutic failure. Examples include structural abnormalities of the urinary tract, physical obstruction or stricture, neurologic deficits that interfere with the normal flow of urine, and the presence of a urinary stone.


In women, most pathogenic bacteria travel an ascending route because of the short length of the female urethra and its proximity to the perianal area. On rare occasions, UTIs are caused by hematogenous spread of pathogens from a distant site of infection. The virulence of the microorganisms, the defense mechanisms of the individual, and the location of the infection all influence the course of the infection.


Bacterial adhesion allows many organisms the opportunity to gain a foothold in the urinary tract. Most gram-negative bacteria responsible for UTIs express molecules on their surfaces that allow them to attach themselves to the bladder mucosa. Type 1 fimbriae, produced by Escherichia coli and other cystitis-causing Enterobacteriaceae, are able to attach to mannose residues on cell membranes. It is these fimbriae that allow bacteria from the gut to attach to the perineum and vagina and thereby make their way to the urethra. Once the bacteria have attached themselves to the bladder mucosa, inflammation and clinical symptoms appear.


The urinary tract of an otherwise healthy individual is relatively resistant to bacterial infection. The urinary system has multiple redundant systems in place to help protect itself from microbial invasion. Normal bladder-emptying mechanisms impede bacterial multiplication. The low pH and high organic-acid concentration of urine make urine capable of inhibiting the growth and proliferation of numerous microorganisms.


The urinary frequency experienced during a UTI is, in part, a physiologic attempt by the body to flush out the microorganisms through increased diuresis. The epithelial cells of the bladder are coated with a type of mucus (uromucoid) that helps prevent the adherence of bacteria to the bladder wall. Tamm-Horsfall protein, produced in the kidney and secreted into the urine, binds specifically to type 1 fimbriated E. coli, the main cause of UTI of women.4 Research has shown that the kidney produces defensins, antimicrobial peptides that play a pivotal role in nonspecific host defense.5



SYMPTOMS OF URINARY TRACT INFECTION


The chief presenting complaints for cystitis in healthy women are dysuria and urinary frequency and urgency without fever or constitutional symptoms. Approximately 20% of women report suprapubic pain. Flank pain, costovertebral-angle tenderness, fever, nausea, and vomiting are more often associated with pyelonephritis, although many patients with pyelonephritis also report lower UTI symptoms. Sometimes a vaginal infection can mimic the symptoms of UTI; however, a woman who complains of dysuria without vaginal discharge most likely has a UTI, not vaginitis.6 When the primary complaint is discomfort during voiding, with virtually no symptoms of postvoid suprapubic pain or urinary frequency, the diagnosis of urethritis should be considered. Box 18-1 lists risk factors for UTI.



Box 18-1 Risk factors for urinary tract infection



image Sexual activity

image Young age

image Use of diaphragm or spermicide

image Pregnancy

image Incomplete emptying of the bladder caused by mechanical or neurogenic malfunction

image Fecal incontinence

image Neuromuscular disease

image Catheterization

image Medical instrumentation

image Obstruction of urinary tract with resultant stasis

image Fecal contamination caused by wiping of perineum from back to front

image Renal abnormalities

image Advanced age

image Underlying disease, especially diabetes and immunocompromise

In women with urethritis, inflammation and infection are limited to the urethra and vagina. The origin of urethritis is usually a sexually transmitted pathogen such as Chlamydia trachomatis, Ureaplasma urealyticum, Neisseria gonorrhoeae, or Trichomonas vaginalis.7



DIAGNOSIS


The evaluation of urine for diagnostic purposes has been used since at least the time of Hippocrates. The color, amount of sediment, smell, and taste of urine assisted ancient healers in their understanding of illness. By the 1830s, microscopes were becoming available to the physician, and examination of the urine became more sophisticated. Today, dipsticks are used to test pH; the presence of ketones, protein, and glucose; specific gravity; and concentrations of bilirubin, urobilinogen, nitrite, leukocyte esterase (LE), and hemoglobin. Direct microscopic examination of fresh or Gram-stained urine and dipstick tests for LE and nitrites offer a quick and effective means of assessing acute, uncomplicated cystitis.


Pyuria without significant bacteriuria suggests urethritis. The LE test has a reported sensitivity of 75% to 96% and specificity of 94% to 98% in the detection of more than 10 leukocytes per high-power field.8 The combination of positive nitrite and LE findings is highly suggestive of a UTI. If both of sets of results are negative, the negative predictive value is 98%, meaning that a UTI is extremely unlikely.9 Urine cultures are often sent for further evaluation in young children, elders, pregnant women, symptomatic men, and anyone with suspected pyelonephritis before antimicrobial therapy is initiated.


A variety of organisms are capable of infecting the urinary tract. Gram-negative bacteria are the major offenders, with E. coli accounting for approximately 80% of infections in patients younger than 50 years.10 Other gram-negative organisms include Proteus, Klebsiella, and Enterobacter. Proteus and Klebsiella are more common in those with urinary tract stones. Serratia and Pseudomonas are often associated with urinary obstruction and prolonged use of indwelling catheters. Infection can be due to gram-positive bacteria, especially Staphylococcus saprophyticus, which is frequently found in the urine of young women. If Staphylococcus aureus is found in a urine culture, one should maintain a high index of suspicion for kidney infection. Atypical organisms such as U. urealyticum and Mycoplasma hominis account for a small number of UTIs.



TREATMENT OF UNCOMPLICATED CYSTITIS


The treatment goals for uncomplicated cystitis are symptom relief, eradication of the offending organism, preventing damage to the kidney, and reducing the likelihood of recurrence. Antibiotics are the mainstay of conventional therapy. Mild illness in patients who are able to maintain oral hydration is generally managed on an outpatient basis with oral antibiotics and follow-up. Patients with more severe illness and those who cannot maintain oral hydration are typically hospitalized for administration of intravenous antibiotics and fluids, especially children younger than 1 year, the elderly, immunocompromised patients, men, and pregnant women.


The Infectious Diseases Society of America convened a committee to systematically review the data on antimicrobial therapy for UTIs and develop treatment guidelines for acute uncomplicated bacterial cystitis and acute pyelonephritis in women. The following is taken from the committee’s recommendations regarding uncomplicated UTI11:


image Most antimicrobials given for 3 days are as effective as the same antimicrobial given for a longer duration. Trimethoprim-sulfamethoxazole, or trimethoprin alone, taken for 3 days is considered the current standard therapy.

image Fluoroquinolones are more expensive than trimethoprim-sulfamethoxazole and trimethoprim, and, in an attempt to postpone emergence of resistance to these drugs, they are not recommended as initial empiric therapy except in communities with high rates of resistance (i.e., 10%-20%) to trimethoprim-sulfamethoxazole or trimethoprim.

Antibiotic resistance is now a major factor in uncomplicated community-acquired UTIs. Resistance to trimethoprim-sulfamethoxazole approaches 18% to 22% in some regions of the United States, and nearly one in three bacterial strains causing cystitis or pyelonephritis is resistant to amoxicillin. Fortunately, for now, resistance to other agents, such as nitrofurantoin and the fluoroquinolones, has remained low, approximately 2%.12 The fluoroquinolones, such as ciprofloxacin, ofloxacin, and levofloxacin, which exert broad-spectrum antibacterial activity against most gram-negative uropathogens, and the more recent members of this class, which are active against gram-positive uropathogens,13 attain very high urinary concentrations, more than 100 times peak plasma levels, making them very effective in UTI treatment.


A 7- to 10-day regimen of oral fluoroquinolone is reasonable for outpatient management of mild to moderate pyelonephritis in the setting of a susceptible causative pathogen and rapid clinical response to therapy. Fluoroquinolones are the first-line treatment of acute uncomplicated cystitis in patients who cannot tolerate sulfonamides or trimethoprim, who live in geographic areas with an incidence of known resistance to trimethoprim-sulfamethoxazole of 10% to 20%, or who have risk factors for such resistance.14 The use of fluoroquinolones is contraindicated in patients younger than 18 years because of the potential for joint toxicity, reported in experiments with young animals. Published pediatric series have shown that frequency of articular side effects varies with age: approximately 0.1% in adults and 2% to 3% in children.15


Nitrofurantoin has been used to treat uncomplicated cystitis for almost 50 years. Use of nitrofurantoin for the empiric treatment of mild cystitis is appropriate from a public health perspective as it does not share cross-resistance with the more commonly prescribed antimicrobials.16 Nitrofurantoin is highly active against the most common uropathogens, E. coli and S. saprophyticus, and exerts some activity against several other uropathogens, including Klebsiella species. Nitrofurantoin is a urospecific drug that reaches high urine concentrations but does not have systemic antimicrobial activity.



TREATMENT CONSIDERATIONS FOR SPECIAL CIRCUMSTANCES



Pregnancy


Pregnancy causes a decrease in ureteral tone, peristalsis, and function of the vesicoureteral valves, all of which increase the risk for upper UTI. The immune system of a pregnant woman is modified to accommodate a semiallogeneic fetus, perhaps making gestational physiologic/immune adaptation an additional risk factor for UTI.17 The incidence of asymptomatic bacteriuria (bacteria in the urine without clinical symptoms) is reported at 2% to 14% during pregnancy. Untreated asymptomatic bacteriuria can lead to fetal and maternal complications such as acute pyelonephritis, hypertension, anemia, preterm labor, low birthweight, and intrauterine growth retardation.18 Approximately 20% to 30% of asymptomatic lower UTIs lead to pyelonephritis during pregnancy. Pregnant women with acute pyelonephritis may experience significant complications, including preterm labor, transient renal failure, acute respiratory distress syndrome, sepsis, shock, and hematologic abnormalities.19 A 3- to 7-day course of antibiotic treatment for asymptomatic bacteriuria during pregnancy is clinically indicated to reduce the risk of pyelonephritis and preterm delivery. Routine screening for asymptomatic bacteriuria during pregnancy is cost-effective, particularly in high-prevalence populations.20



Children and Infants


Recurrent urinary tract infections (RUTIs) in children often cause greater morbidity and long-term consequences than they do in adults. UTIs in children can lead to pyelonephritis and, over time, renal scarring. Renal scarring can lead to impaired renal function, hypertension, and end-stage renal disease. A thorough medical evaluation is essential for any child with RUTIs.



Older Patients


UTIs are the second most common infection among noninstitutionalized older individuals (respiratory tract infections are most common). Factors that predispose a postmenopausal woman to UTI include urinary incontinence, cystocele, increased postvoiding residual urine, and a history of premenopausal UTI. Management of UTI in older individuals should generally involve urine culture followed by a longer course of treatment (7 to 14 days).



PREVENTION



Prevention of RUTIs


Since up to 30% of women will experience a recurrence within 3 to 4 months of an initial infection, prevention is an important goal. In the United States, more than 11 million women each year receive antimicrobials for the treatment of UTI, at a cost of more than $1.6 billion.3 Both pharmacologic and nonpharmacologic approaches have been investigated. Although antimicrobials are effective in preventing recurrence of UTI, concerns have been raised about the risk of resistant bacteria. Practitioners often offer prophylactic antimicrobials to women who have more than three UTIs per year, to be used daily, at a low dose, or after sexual intercourse.



Nonpharmacologic Options



Dietary considerations.


Dietary habits may be a risk factor for UTI recurrence in women, and dietary interventions may play a role in prevention. Frequent consumption of fresh juices, especially berry juices, and fermented milk products containing probiotic bacteria is associated with a decreased risk of UTI recurrence.21 Clinical data, however, for these dietary interventions are mixed, although one could hardly argue against their use in the clinical setting given their safety and other health benefits.

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Nov 4, 2016 | Posted by in OBSTETRICS | Comments Off on 18: Urinary Tract Infection

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