How Best to Treat Urinary Tract Infections in Adults:

Urinary tract infections (UTIs) are among the most common infections seen in the primary care setting, and they also account for a large number of hospital infections.^1-3 UTIs are the leading cause of bacteremia in hospitalized patients and are a significant cause of morbidity in all age groups. The estimated annual cost associated with UTIs in the United States is approximately $1.6 billion.⁴

Management considerations include interpretation of urinalysis and culture results, decisions about when urine culture may be omitted, and the choice and length of antibiotic therapy. A rational approach to the management of UTIs will likely decrease the morbidity and costs associated with this condition. It will also help reduce the excessive use of antibiotics and the continued increase in drug resistance.

In this article, we review the diagnosis and treatment of uncomplicated and complicated UTI in young women, in men, and in those with urinary catheters.

CLASSIFICATION OF UTIs

UTIs have traditionally been divided into 2 groups-uncomplicated and complicated-depending on severity. They can also be classified based on the affected organ. A number of studies and reviews categorize UTIs based on the clinical syndrome and patient characteristics.^1-3,5 This last classification is preferred because it divides patients into groups based on clinical factors, epidemiology, impact on morbidity, and approach to diagnosis and management.

The principal patient groups are young women, men, children, and patients at risk for complicated UTI. A useful classification of UTIs by clinical syndromes is as follows:

Asymptomatic bacteriuria.

Acute cystitis, recurrent cystitis, and acute pyelonephritis in young women.

UTI in men.

Complicated UTI.

Complicated UTIs are those that occur in children, in persons who are elderly, diabetic, or immunosuppressed, and in those with a structurally abnormal urinary tract or other comorbidity. Patients with abnormal urinary tracts include those with obstructive lesions, foreign bodies, and post-genitourinary procedure instrumentation, and those with dysfunctional voiding attributable to neurologic illnesses. Complicated UTIs may also be caused by pathogens that are resistant to commonly used antibiotics and those associated with the use of urinary catheters.^1-3,5 Catheter-associated UTIs have specific characteristics and will be discussed as a separate entity.

The presence of leukocytes, bacteria, or nitrates in the urine and positive results on a leukocyte esterase test indicate infection. The diagnosis of UTI has traditionally been based on urine culture results that show more than 10⁵ colony-forming units (CFU)/ mL. However, lower numbers of CFU and the presence of symptoms have a high positive predictive value in certain patients. The urinary dipstick test may be diagnostic in the case of acute uncomplicated cystitis in young women.

ASYMPTOMATIC BACTERIURIA

An overview of treatment strategies is provided in Table 1.

The presence of more than 10⁵ CFU/mL in the urine of a person without symptoms constitutes asymptomatic bacteriuria. The incidence of this condition is high in elderly persons, but studies have not demonstrated a decrease in the number of symptomatic infections when asymptomatic bacteriuria is treated. Screening and treatment of asymptomatic bacteriuria are recommended for pregnant women, persons who are about to have genitourinary surgery, and those who have undergone renal transplantation.^1,2,6-9 The choice of antibiotic therapy is based on susceptibility. A 3-day course of amoxicillin, a cephalosporin, nitrofurantoin, or trimethoprim-sul- famethoxazole (TMP-SMX) is usually effective.^1,2,7

UTI IN YOUNG WOMEN

More than half of all women have at least 1 episode of UTI during their lifetime.^10,11 The organisms most frequently implicated in UTIs in women are Escherichia coli, Staphylococcus saprophyticus, Proteus mirabilis, and Klebsiella pneumoniae. The principal clinical syndromes are acute cystitis, recurrent cystitis, and acute pyelonephritis. Women are at higher risk than men for both uncomplicated cystitis and pyelonephritis. The higher risk in women has been explained by anatomy, sexual activity, and the use of diaphragms and spermicides. Acute and recurrent cystitis, once identified, can be treated empirically without microbiologic confirmation.

Acute cystitis. This is the likely diagnosis in a patient with dysuria, increased urinary frequency, and positive results on urinalysis. A urine culture with more than 10³ CFU/mL is diagnostic of UTI in a young woman with urinary tract symptoms.^1,2,12 However, there is no need to obtain a urine culture in women at low risk who have no history of a recent UTI and no symptoms that suggest vaginitis or cervicitis.^1,2,13 In these women, a urine dipstick test that is positive for nitrates or leukocyte esterase is considered diagnostic.

Treatment of acute uncomplicated cystitis in young women without risk factors may be initiated by telephone consultation without diagnostic testing. This method is safe and cost-effective and has become increasingly common among primary care physicians.^1,2,10,14,15 These infections may be treated with a 3-day course of an antibiotic, such as TMP-SMX, a fluoroquinolone, or TMP alone. Single doses of these antibiotics have not demonstrated similar efficacy.¹⁶ A 7-day course of nitrofurantoin is another option. A single dose of fosfomycin may also be used, but it is less effective than TMP-SMX or fluoroquinolones.^1,16,17 In women who are pregnant or who have diabetes, or when symptoms have been present for more than a week, a 7-day course may be indicated.^1,2

Recurrent cystitis. This condition occurs most commonly in association with coitus, especially with exposure to spermicides, condoms, or diaphragms. Prophylaxis is recommended in women with more than 3 episodes per year or 2 episodes within 6 months, provided the urine culture result is negative 2 weeks after treatment is completed.^2,10,17 A urine culture is recommended to differentiate between relapse and recurrence. Relapse is caused by the same organism as the original infection and can be associated with anatomic abnormalities of the urinary tract. Recurrences are caused by different organisms.

Treatment and prophylaxis options in this group include self-treatment with a 3-day course of an antibiotic, postcoital prophylaxis with a single dose of antibiotic, or long-term low-dose antimicrobial therapy. TMP-SMX, nitrofurantoin, TMP alone, or a fluoroquinolone are effective choices (Table 2).^2,10,17 There is no evidence that postcoital voiding, poor urinary hygiene, urinary frequency, or wiping patterns have any effect on the risk of recurrence.¹⁰

Acute pyelonephritis. In young women, this conditionusually presents with back pain and costovertebral tenderness on physical examination. Fever, nausea, vomiting, bacteremia, and leukocytosis are present in severe cases. Urinalysis and urine cultures can confirm the diagnosis and help direct antimicrobial therapy. Oral outpatient therapy usually suffices for patients with mild pyelonephritis; intravenous antibiotics are indicated for severe disease. TMP-SMX may be used, but because of increased resistance in certain geographic areas, fluoroquinolones are rapidly becoming the treatment of choice. Amoxicillin-clavulanate is also effective. The recommended duration of therapy is 14 days.^1,2,10

UTI IN MEN

Most UTIs in men occur in the elderly and are secondary to bladder outlet obstruction and prostatic disease. Evidence no longer supports the view that UTIs in young men are associated with structural urinary tract abnormalities and therefore should be considered complicated. Cystitis that sometimes mimics urethritis may develop in young men. Risk factors include anal sex, lack of circumcision, advanced AIDS, or having a sexual partner with vaginal colonization by uropathogens.^1,6,7 Men with pyelo- nephritis or recurrent infections and those who do not respond to treatment require further urologic evaluation.^1,2

A urine culture with more than 10³ CFU/mL may be diagnostic of infection in the presence of symptoms. The most commonly found culprit organism is E coli. A 7-day course of TMP-SMX, TMP, or a fluoroquinolone is the recommended therapeutic regimen; the choice is based on the antibiogram. In pyelonephritis, therapy is continued for 14 days. In bacterial prostatitis, therapy is continued for 6 to 12 weeks.

COMPLICATED UTI

The clinical presentation of complicated UTI ranges from localized infection, such as cystitis, to systemic infection, such as urosepsis and septic shock. These infections are caused by a broad spectrum of organisms that often are resistant to widely used antibiotics. E coli is the most commonly isolated organism. However, pathogens from species such as Klebsiella, Enterobacter, Serratia, Proteus, Providencia, Pseudomonas, and Candida may also cause complicated UTIs.

Empiric antibiotic therapy is started as soon as possible in patients at risk for complicated UTI. Therapy can be modified once antimicrobial susceptibility has been determined. An oral fluoroquinolone is appropriate in mild cases; for severe infection, intravenous antibiotics are recommended. The options include fluoroquinolones, TMP-SMX, a third-generation cephalosporin, aminoglycosides, or imipenem. In patients at risk for Pseudomonas infection, an antipseudomonal agent is initiated empirically.

The recommended length of treatment for complicated UTIs is at least 14 days. If no improvement is seen after 72 hours of intravenous antibiotic therapy, imaging studies are warranted to rule out an obstruction or abscess. Follow-up cultures are recommended 2 weeks after completion of treatment.

UTIs IN PATIENTS WITH URINARY CATHETERS

UTIs associated with the use of urinary catheters are an important cause of morbidity, mortality, and increased costs-especially in hospitalized or institutionalized patients.

Identification of situations in which a long-term or temporary urinary catheter is indicated is vital in reducing the risk of UTIs and associated complications. Long-term catheterization may be indicated in patients with urinary obstruction not amenable to medical or surgical treatment, patients with neurogenic bladder who have urinary retention, and incontinent patients with intractable skin breakdown, and as palliative care for terminally ill patients to avoid multiple bed linen changes. Short-term catheterization is indicated for patients expected to undergo surgery of the urinary tract or contiguous structures, in patients with acute urinary retention, and in critically ill patients when exact urinary output measurement is needed.^1,18-20

Prevention is the best way to reduce the incidence of catheter-associated UTI. Alternatives to indwelling catheters include intermittent catheterization in patients with spinal cord injuries, condom catheters in incontinent men with intact voiding reflex, and suprapubic catheters in patients expected to undergo urologic or gynecologic surgery. These alternatives are widely used, and some studies have demonstrated a decrease in the incidence of UTIs.^19,20

The principal risk factor for UTI is bacteriuria. A urine culture with more than 100 CFU/mL in a patient with symptoms indicates infection. Because bacteriuria occurs in all patients with long-term catheters, treatment is initiated only in the presence of symptoms. Treatment may be considered in patients undergoing genitourinary instrumentation and in those with urinary tract abnormalities.

Treatment of UTI in a patient with a urinary catheter requires replacement of the catheter and selection of antibiotics based on the extent of the infection and the result of the urine culture. Empiric antibiotic treatment is recommended in symptomatic patients. The duration of treatment is similar to that in patients with other complicated UTIs.^19,20 n

References:

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