Acute uncomplicated urinary tract infection and acute pyelonephritis are very common infections affecting many women throughout their lives. The determinants of infection have been well described and current strategies to prevent recurrent infections are highly effective. While antimicrobial management is straightforward for most episodes, the evolution of antimicrobial susceptibility of E. coli in community-acquired infection requires continuing re-evaluation of appropriate empiric therapy.
Acute uncomplicated urinary tract infection, also called acute uncomplicated cystitis, is a bladder infection that occurs in women who have normal structure and function of the genitourinary tract . These same women are at risk for acute nonobstructive pyelonephritis, also called acute uncomplicated pyelonephritis. Women who experience recurrent acute uncomplicated urinary infection at a younger age continue to be at risk for recurrent infection after menopause , suggesting the determinants of uncomplicated infection in younger women continue to contribute in older women. Similarly, acute cystitis occurring in diabetic women without long-term complications of their diabetes, such as neuropathy, may be considered uncomplicated infection and managed as such. Acute urinary infection occurs rarely in young men with a normal genitourinary tract. When it does occur, risk associations include men who have sex with men or a sexual partner with vaginal colonization with E. coli . Lack of circumcision may also be a risk, but this association is more controversial . These infections are so infrequent, however, that urinary infections in men should always be managed as complicated urinary infection.
Acute uncomplicated urinary infection
Epidemiology
As many as 10% of women experience at least one episode of acute uncomplicated urinary infection in a year, and 60% have at least one episode during their lifetime . The peak incidence of infection occurs in young, sexually active, women aged 18 to 24 years . Recurrent episodes are experienced by as many as 5% of women at some time during their life . In a primary care setting, 44% of women presenting with an infection experienced a second infection within 1 year ; 21% of college women with a first urinary infection had a second infection within 6 months .
Acute cystitis is benign from the perspective of long-term outcomes, but is associated with substantial disruption in a woman’s life with each episode. College women reported an average of 6.1 symptom days and 2 to 4 restricted activity days with an episode of cystitis, and 1.2 work days lost . In a recent Canadian study of subjects presenting to family physicians, 63% of women reported the infection had an impact on their usual activities, with a mean duration of 4.9 days of symptoms .
Pathogenesis
Host factors
A genetic association is supported by the observation that women who experience recurrent cystitis are more likely than those without infections to have first degree female relatives (mothers, sisters, daughters) who also experience recurrent urinary tract infection . Nonsecretor status may explain some of this predisposition, especially in older women . Other potential genetic associations are not yet fully characterized.
Behavioral practices are strongly correlated with infection in young women. From 75% to 90% of episodes of cystitis in young sexually active women are attributable to sexual intercourse, with the frequency of infection correlating with the frequency of intercourse . It is unusual for young women who are not sexually active to experience uncomplicated urinary infection . The use of a spermicide for birth control is also a major behavioral risk for infection. The frequency of spermicide use correlates with the frequency of recurrent infection, independent of intercourse frequency . Other behaviors previously considered risk factors for urinary infection have not been confirmed in repeated epidemiologic studies . These activities include the use of birth control pill or condoms, postcoital voiding, type of underwear used, personal hygiene after voiding or defecating, or taking a bath rather than shower.
Risk factors for uncomplicated urinary infection differ in postmenopausal women. In prospective studies sexual activity is not associated with recurrent infection . The strongest and most consistent risk factor for postmenopausal women is a history of urinary infection at a younger age . Other potential contributors include diabetes and nonsecretor status . Chronic incontinence is consistently associated with urinary infection in postmenopausal women . However, incontinence suggests the presence of voiding abnormalities, and these women would be assumed to have functional abnormalities consistent with complicated urinary infection.
Microbiology
Acute uncomplicated urinary infection is primarily a disease caused by extraintestinal pathogenic Escherichia coli ; this organism is isolated in 80% to 85% of episodes . Organisms that are capable of colonization and subsequent infection are characterized by a restricted number of phylogenetic E. coli groups and diverse virulence factors . There is considerable overlap in putative virulence factors among strains isolated from symptomatic or asymptomatic infection . The most important virulence factor for establishing bladder infection is likely the type 1, mannose sensitive, fimbria, which attaches to receptors on uroepithelial cells . Unique strains of uropathogenic E. coli circulate among members of households , and may be isolated from clonal outbreaks in a community or larger geographic area .
Staphylococcus saprophyticus is the second most common organism isolated, although only 5% to 10% of episodes are attributed to this organism. It is isolated virtually only in the setting of acute uncomplicated cystitis. The genome of this bacteria has recently been characterized, and genetic elements contributing to success as a uropathogen have been described. These include an adhesin, transport systems supporting growth in urine, and a urease . Other organisms are isolated infrequently. Group B streptococcus has a predilection for pregnant or diabetic women. Proteus mirabilis is uncommon, but may be isolated somewhat more frequently in postmenopausal women .
Antimicrobial resistance
Antimicrobial susceptibility of E. coli evolves continuously in response to antimicrobial pressure . Increasing resistance has compromised the efficacy of ampicillin, cephalosporins, and trimethoprim/sulfamethoxazole (TMP/SMX), and increasing resistance to fluoroquinolones is now being reported . The expansion of extended spectrum beta lactamase (ESBL) producing E. coli , usually also resistant to TMP/SMX and fluoroquinolones, is a current concern . Resistance in community isolates occurs through both clonal expansion, as described with a TMP/SMX resistant E. coli strain in the United States , and through emergence in multiple distinct strains secondary to horizontal gene transfer, as reported in a study of isolates from Canada and Europe . Prior recent antimicrobial therapy is the most important determinant for isolation of a resistant organism . Antimicrobial pressure is attributable not just to prior treatment of urinary infection, but also antimicrobial use for other indications, such as the widespread use of fluoroquinolones for respiratory tract infection, or antimicrobial use in animal husbandry .
Origin of infection
Development of acute uncomplicated urinary infection follows colonization of the vagina and the periurethral area by uropathogenic E. coli . Colonization is characterized by replacement of the H 2 O 2 producing lactobacilli (which maintain an acid vaginal environment) with E. coli and other organisms . Spermicide use and recent antimicrobial therapy may facilitate these changes in flora, explaining the association of these behaviors with infection.
Recent studies in mice have reported that E. coli can persist within bladder uroepithelial cells. Early in the course of infection E. coli are internalized into these cells, which are then sloughed as part of the healing process . It has been proposed that organisms that may persist within uroepithelial cells in the bladder are a reservoir for recurrent infection. The relevance of these observations to human beings has not yet been determined.
Diagnosis
Clinical
Acute uncomplicated urinary infection has a characteristic clinical presentation. New onset frequency, dysuria, and urgency, together with the absence of vaginal discharge or pain, has a positive predictive value of 90% for acute cystitis . Infection may also be associated with hematuria. For older women, new or increased incontinence is also a common symptom. The presentation is so characteristic that women with a history of recurrent infection are over 90% accurate in self-diagnosis of infection .
Laboratory
The microbiologic diagnosis of urinary tract infection requires quantitative isolation of a uropathogenic organism from an appropriately collected urine specimen. A quantitative count of greater than or equal to 10 5 colony forming units (CFU) per mL (greater than or equal to 10 8 CFU/L) was initially proposed as the diagnostic criteria, based on studies primarily performed in asymptomatic women or women presenting with pyelonephritis. However, 30% to 50% of women presenting with clinical symptoms consistent with acute cystitis have lower quantitative counts, usually 10 3 CFU/mL to 10 5 CFU/mL . Thus, greater than or equal to 10 3 CFU/mL of a uropathogen is the accepted microbiologic diagnostic criteria for acute cystitis . As many as 10% to 20% of symptomatic women have negative urine cultures, presumably because of organism counts below the threshold for laboratory isolation. The clinical response to treatment for these women is similar to that of women with positive urine cultures .
Given the predictable microbiology, the limitations in interpretation of the quantitative urine culture, the reliable clinical diagnosis, and the 24 to 48 hour delay in culture results, it is recommended that empiric treatment be initiated based on symptoms alone, without consistent collection of a pretherapy urine specimen . A specimen should be obtained, however, for women with an atypical presentation, with early symptomatic recurrence after therapy, or when pyelonephritis is a potential diagnosis.
Pyuria is virtually a universal accompaniment of women with acute uncomplicated cystitis . Documentation of pyuria supports the diagnosis and may be useful for evaluation of women who present with atypical symptoms. However, routine measurement of pyuria is not consistently recommended or necessary for management . The absence of pyuria does not exclude the diagnosis of urinary infection in women with consistent symptoms .
Treatment
Natural history
Placebo controlled clinical trials have characterized the natural history of untreated acute cystitis . Among 277 women treated with placebo, 28% were free of symptoms at 1 week and 45% had negative cultures by 6 weeks . In another study, 54% of women who received placebo were asymptomatic by 3 days, and 52% at 7 days . These studies suggest about half of women will have spontaneous clinical and microbiologic resolution of infection within a few days or weeks. Despite this, antimicrobial treatment substantially shortens the duration of symptoms. The clinical cure at 3 days was 77% with nitrofurantoin therapy, compared with 54% with placebo, and at 7 days 88%, compared with 52% with placebo . In a recent clinical trial, 54% of subjects reported symptom improvement by 6 hours after therapy, 87% by 24 hours, and 91% by 48 hours . By the fourth day of effective treatment 72% of patients had symptom resolution, and by the tenth day, 84% .
Antibiotic selection
Many antimicrobial regimens are effective for treatment ( Table 1 ). The most common antimicrobials used include nitrofurantoin, TMP/SMX or trimethoprim alone, fluoroquinolones, beta-lactam antimicrobials including amoxicillin, cephalosporins and pivmecillinam, and fosfomycin trometamol. The efficacy of different antimicrobials varies, particularly for shorter durations of therapy. Beta-lactam antimicrobials, including amoxicillin, amoxicillin/clavulanic acid, and cephalosporins, are consistently less effective than TMP/SMX or fluoroquinolones . In addition, nitrofurantoin and fosfomycin/trometamol are 5% to 10% less effective than 3 days of TMP/SMX or fluoroquinolone .
| Agent | Dose | Duration |
|---|---|---|
| Amoxicillin | 500 mg tid | 7 days |
| Amoxicillin/clavulanic acid | 500 mg tid | 7 days |
| Cephalosporins: | ||
| Cephalexin | 250 mg–500 mg qid | 7 days |
| Cefuroxime axetil | 500 mg bid | 7 days |
| Cefixime | 400 mg od | 7 days |
| Cefpodoxime proxetil | 100 mg bid | 3 days |
| Fluoroquinolones: | ||
| Norfloxacin | 400 mg bid | 3 days |
| Ciprofloxacin | 250 mg–500 mg bid | 3 days |
| Extended release | 500 mg od | 3 days |
| Ofloxacin | 200 mg | 3 days |
| Levofloxacin | 250 mg–500 mg bid | 3 days |
| Nitrofurantoin macrocrystal | 50 mg–100 mg qid | 7 days |
| Monohydrate/macrocrystals | 100 mg bid | 7 days |
| Pivmecillinam | 400 mg bid | 3 days |
| 200 mg bid | 7 days | |
| Fosfomycin trometamol | 3 g | Single dose |
| TMP/SMX | 160/800 mg bid | 3 days |
| Trimethoprim | 200 mg bid | 3 days |
Antimicrobial susceptibility is, of course, an important determinant of efficacy. Higher failure rates are observed for infections with TMP/SMX-resistant organisms treated with TMP/SMX . In European countries where trimethoprim alone is frequently used, resistant rates over 20% are associated with high failure rates with empiric trimethoprim therapy . E. coli strains generally remain susceptible to fluoroquinolones. However, the expansion of ESBL producing E. coli in community-acquired infections may limit future use . Optimal treatment of urinary infection caused by ESBL producing E. coli is not well defined. Nitrofurantoin and fosfomycin trometamol remain effective for most of these strains. Pivmecillinam and amoxicillin/clavulanic acid may also be effective for some of these strains , although clinical experience is limited.
Duration of therapy
The recommended duration of therapy for acute cystitis is 3 days when trimethoprim, TMP/SMX, or a fluoroquinolone (norfloxacin, ciprofloxacin, levofloxacin) is prescribed . For nitrofurantoin, 7-days therapy is recommended. Fosfomycin/trometamol is marketed only as single dose therapy. Pivmecillinam is recommended for treatment of 3 or 7 days; other beta-lactam antimicrobials are usually given as 7-day regimens, if used. A recent meta-analysis concluded that the 3-day therapy regimens are as effective as longer courses for resolution of symptoms, but may be less effective for microbiologic resolution . However, randomized, placebo controlled clinical trials support the equivalent efficacy and fewer adverse effects of the shorter duration of therapy.
A single dose is quite effective for selected antimicrobials in addition to fosfomycin trometamol . Cure rates with TMP/SMX and fluoroquinolones are reported to be 80% to 95% with a single dose. However, reviews and meta-analyses consistently report single dose therapy is marginally less effective than 3 days for TMP/SMX or fluoroquinolones . In addition, patient and physician acceptance of a single dose regimen is problematic, as symptoms persist for several days after treatment while inflammation in the bladder resolves. Gatifloxacin was recently marketed with an indication for single dose therapy ; however, this agent has now been removed from the market because of serum glucose abnormalities.
Systematic reviews have concluded that a 3-day duration of therapy is not as effective for older, as compared with younger women . Postmenopausal women, however, have poorer outcomes with any duration of antimicrobial therapy compared with premenopausal women . A recent randomized, placebo controlled, trial compared 3 to 7 days of ciprofloxacin for acute cystitis in older women without complicating factors. The mean age of study participants was 78.5 years. Clinical and microbiologic outcomes were similar with either treatment duration, while 3 days of therapy was associated with significantly fewer adverse effects . Thus, 3 days of therapy is appropriate for treatment of postmenopausal women with presumed uncomplicated infection.
Guidelines
Current guideline recommendations are summarized in Table 2 . The Infectious Diseases Society of America (IDSA) guidelines, published in 1999, recommend TMP/SMX for 3 days as a first line treatment for acute uncomplicated cystitis . However, if the prevalence of resistance of E. coli to TMP/SMX for isolates from acute uncomplicated cystitis in a region is over 20%, an alternate antimicrobial should be selected for empiric treatment: nitrofurantoin for 7 days or one of the fluoroquinolones (norfloxacin, ciprofloxacin, levofloxacin) for 3 days would be recommended. The European Union guideline for acute uncomplicated cystitis was updated in 2006 . This document also concludes that TMP/SMX for 3 days should be first line therapy, but emphasizes that knowledge of local resistance prevalence is essential in choosing empiric therapy. Effective alternate regimens for treatment of acute uncomplicated urinary infection are also recommended.
| IDSA | European Union |
|---|---|
| First line | |
| TMP/SMX, 3 days | TMP/SMX, 3 days |
| Alternatives | |
| Trimethoprim, 3 days | Cefpodoxime proxetil, 3 days |
| Fluoroquinolone (ofloxacin, norfloxacin, ciprofloxacin), 3 days | Ciprofloxacin, 3 days |
| Fosfomycin trometamol, single dose | |
| Levofloxacin, 3 days | |
| Norfloxacin, 3 days | |
| Ofloxacin, 3 days | |
| Pivmecillinam, 7 days | |
| Trimethoprim, 5–7 days | |
| Others | |
| Fosfomycin trometamol, single dose | Nitrofurantoin, 5–7 days |
| Nitrofurantoin, 7 days | Pivmecillinam, 3 days |
| Trimethoprim, 3 days | |
Managing recurrent infection
Delivery of care
Several management strategies have been described which allow prompt and efficient access to treatment for women with recurrent infection, while limiting costs. Effective approaches include telephone assessment and treatment by a physician or nurse practitioner following an algorithm , or use of an interactive computer by the patient . The general features of these strategies include no urine specimen collection, phone prescription without in-person assessment, and follow-up only if symptoms persist or recur early following treatment . These approaches have been documented to be efficient, with increased patient satisfaction and cost savings, while treatment outcomes are equivalent to standard management by physician visit . However, the studies were undertaken in relatively controlled settings with appropriate resources to support the program. The extent to which they are generally applicable may require evaluation in more diverse settings.
Self-treatment
Self-treatment by women who experience recurrent infection is also an effective strategy . This approach may be particularly useful for women with infrequent recurrences, or who are concerned they may develop infection while traveling or otherwise unable to access usual health care. Women with recurrent urinary infection are over 90% accurate in identifying a new episode, and self-treatment is effective at least 85% of the time. Both single dose or 3 days of self-treatment with TMP/SMX or a fluoroquinolone have been shown to be effective, although current recommendations would be for a 3-day course. Women should be advised that failure of symptom resolution with treatment, or early recurrence following therapy, requires physician assessment.
Prevention
The first consideration in prevention is to address modifiable behavioral practices, particularly discontinuing the use of spermicide. Other effective strategies are generally considered as antimicrobial or nonantimicrobial ( Table 3 ).
| Strategy | Efficacy |
|---|---|
| Long-term low dose antimicrobial prophylaxis | |
| • TMP/SMX 40/200 mg (1/2 regular strength) daily or eod | 95% |
| • TMP 100 mg daily | 95% |
| • Nitrofurantoin 50 mg or macrocrystals 100 mg daily | 95% |
| • Norfloxacin 200 mg daily or eod | 95%–100% |
| • Ciprofloxacin 125 mg daily | >95% |
| • Cephalexin 250 mg–500 mg daily | 95% |
| Postcoital antimicrobial prophylaxis | |
| • Cephalexin 250 mg | >95% |
| • TMP/SMX 40/200 mg or 80/400 mg | 90%–95% |
| • Trimethoprim 100 mg | >95% |
| • Nitrofurantoin 50 mg or 100 mg | >95% |
| • Norfloxacin 200 mg | >95% |
| • Ciprofloxacin 125 mg | >95% |
| Nonantimicrobial strategies | |
| • Cranberry or lingonberry juice or other products | 20%–30% |
| • Probiotics | investigational |
| • Vaccination | investigational |
| • Topical estrogen for postmenopausal infections | 0%–30% |
Low dose antimicrobial therapy remains an effective intervention to manage frequent, recurrent, acute uncomplicated urinary tract infection . The antimicrobial may be given as continuous daily or every-other-day therapy, usually at bedtime, or as postcoital prophylaxis. First line treatments are nitrofurantoin or TMP/SMX. Fluoroquinolone antimicrobials are effective, but should be reserved for women who are unable to tolerate first line agents or who experience recurrent infection with resistant organisms while receiving first line regimens. The initial suggested duration of prophylaxis is 6 months; however, 50% of women will experience recurrence by 3 months after discontinuation of the prophylactic antimicrobial. When this occurs, prophylaxis may be reinstituted for as long as 1 or 2 years and remain effective.
Nonantimicrobial strategies to prevent recurrent infection are being developed and evaluated (see Table 3 ) . Daily cranberry products (juice or tablets) or lingonberry juice decreases the frequency of recurrent infection by about 30%, compared with 90% to 95% effectiveness of antimicrobial use . Vaccination strategies, and probiotics to re-establish vaginal colonization with H 2 O 2 producing lactobacilli, are also being investigated, but studies to date do not report convincing efficacy . Topical vaginal estrogen is a potential intervention to decrease recurrent episodes for postmenopausal women, but also remains controversial . This approach may benefit some women, but is not as effective as antimicrobial prophylaxis. Systemic estrogen therapy is consistently associated with no benefit or an increased risk for infection .
Acute nonobstructive pyelonephritis
Acute nonobstructive pyelonephritis occurs in the same women who experience acute uncomplicated cystitis, but is less common. The relative frequency of pyelonephritis to cystitis for women with recurrent acute uncomplicated urinary infection was 18 to 1 in a Seattle urinary infection referral cohort, and 29 to 1 in a Finland primary care cohort . The genetic and behavioral risk factors associated with pyelonephritis are similar to those for acute, uncomplicated infection . For premenopausal women, these include sexual intercourse, prior urinary infection, new sexual partner, recent spermicide use, urinary infection history in the mother, diabetes, and recent incontinence. The strongest association is with sexual intercourse. A recent study reports a familial susceptibility to pyelonephritis that may be attributable to low expression of CXCR1, an interleukin (IL)-8 receptor .
Pathogenesis
Microbiology
E. coli are isolated from about 90% of episodes of acute nonobstructive pyelonephritis. These pyelonephritogenic strains have unique virulence characteristics. The most consistent virulence factor is the presence of the P pilus, a Gal (∞ 1–4), Gal-β disaccharide galabiose adhesin . There are several other virulence factors described, including hemolysin and Aerobactin. Virulence characteristics may cluster in pathogenic islands in the genome of uropathogenic strains.
The specific mechanisms by which E. coli produce pyelonephritis are not fully understood. In a normal urinary tract without reflux, virulence characteristics of infecting organisms must facilitate ascension from the bladder to the kidney, and subsequent adherence to renal cells in the medulla. Lipopolysaccharides released from the cell wall are thought to trigger an inflammatory response, which produces the clinical manifestations of illness.
Immune and inflammatory response
Pyelonephritis is characterized by the systemic and local production of cytokines and other inflammatory markers. These include proinflammatory cytokines, such as IL-6, IL-1 beta, and tumor necrosis factor (TNF)-alpha. IL-6 and IL-8 in serum and urine of patients are elevated in acute pyelonephritis , as are serum levels of granulocyte colony-stimulating factor (G-CSF) and IL-10 . The IL-6 and G-CSF levels correlate with the presence of hemolysin and cytotoxic necrotizing factor in the infecting E. coli strain . Serum levels of C-reactive protein, IL-6, and TNF-alpha are all elevated before antimicrobial therapy . At 24 hours following initiation of antibiotics, the C-reactive protein and serum TNF-alpha remain elevated, as well as urinary N-acetyl-beta glucosaminidase, alpha-1 microglobulin, and beta-2 microglobulin. The serum IL-6 and urinary IL-6, IL-8, albumin, and immunoglobulin levels decrease significantly by 24 hours. The urine level of IL-8 at presentation and serum soluble IL-6 receptor level at 2 weeks may be prognostic markers for after-treatment recovery of the glomerular filtration rate . The intensity of the inflammatory response in children with pyelonephritis correlates with development of renal scars and subsequent renal dysfunction, but this association has not yet been documented for adult women .
Diagnosis
Clinical
The clinical presentation of acute nonobstructive pyelonephritis is often straightforward, with signs and symptoms of costovertebral angle pain and tenderness, with or without fever, or lower tract irritative symptoms. However, the severity of symptoms at presentation is variable, with a spectrum ranging from predominantly lower tract symptoms with mild localizing costovertebral angle findings to severe systemic symptoms with bacteremia and sepsis. High fever, intense pain, and nausea and vomiting are common with severe presentations. The sepsis syndrome and septic shock are uncommon in women with acute uncomplicated pyelonephritis. Women presenting with more severe illness should always be considered, potentially, to have obstruction of the genitourinary tract rather than uncomplicated infection.
Urine culture
An appropriately collected urine specimen should always be obtained before the initiation of antimicrobial therapy. The quantitative count of greater than or equal to 10 4 CFU/mL, together with consistent symptoms of pyelonephritis, is considered diagnostic . In addition to confirming the diagnosis, organism identification and antimicrobial susceptibility testing provides assurance that the initial empiric therapy is appropriate, and allows selection of a specific oral agent to complete therapy after an initial response to parenteral therapy.
Other laboratory tests
A complete blood count, blood urea, and creatinine should be obtained. The leukocyte count is a measure of disease severity, and can be monitored as an indicator of infection resolution and response to therapy. Renal failure is unusual with uncomplicated pyelonephritis, but acute or chronic renal impairment must always be excluded.
When blood cultures were obtained uniformly from all women with uncomplicated pyelonephritis presenting to a Spanish hospital, 25.2% were positive . For women or children admitted to an American hospital with uncomplicated pyelonephritis, 50% had blood cultures obtained and 10.4% of these were bacteremic . Positive blood cultures were concordant with urine cultures in over 95% of cases, and clinical outcomes did not differ for women with or without bacteremia . Thus, obtaining routine blood cultures for all patients with pyelonephritis does not have clinical utility. However, any women with presentations including high fever, hemodynamic instability, or severe nausea and vomiting, or in whom the diagnosis is uncertain, should have blood cultures obtained.
C-reactive protein and procalcitonin levels are elevated with acute pyelonephritis . The measurement of levels of these proteins as diagnostic tests or prognostic indicators has been studied in pediatric populations. It is not clear whether the tests are useful in management of women with nonobstructive pyelonephritis. In one study, serum procalcitonin level at presentation did not predict a poor outcome .
Diagnostic imaging
It has been suggested that all women presenting with acute pyelonephritis require imaging of the genitourinary tract . Ultrasound studies are used most frequently, but are relatively insensitive. They usually show enlargement of one or both affected kidneys, with focal complications identified in less than 10% . Computerized tomography (CT) may be the imaging modality of choice. It will identify calculi, gas, hemorrhage, calcification, obstruction, renal enlargement, and inflammatory masses. Contrast enhanced scans are recommended; helical and multislice CT allow study of different phases of contrast excretion . It is not clear, however, that routine imaging for all subjects has utility in management of infection or leads to improved outcomes . Diagnostic imaging is useful when the diagnosis is uncertain, with more severe presentations when obstruction or abscess must be expeditiously excluded, or if there is inadequate response or rapid recurrence following appropriate therapy and an underlying abnormality must be excluded . On the other hand, a woman presenting with mild or moderate symptoms, who responds promptly to antimicrobial therapy with no recurrence, is unlikely to benefit from imaging studies. Thus, diagnostic imaging should be used selectively.
Management
Hospitalization
The initial assessment of any woman presenting with acute nonobstructive pyelonephritis includes evaluation of the severity of illness. Temperature, blood pressure, and symptoms such as vomiting should be noted. The majority, probably 80%, of young women with acute pyelonephritis do not require hospitalization and are effectively treated with oral therapy, often with an initial intravenous dose of antimicrobials. Women should be considered for hospitalization and initial parenteral therapy if they are hemodynamically unstable, have severe nausea and vomiting, or if there are concerns about absorption of oral antimicrobials. Appropriate supportive management for hypotension, vomiting, and pain control should be initiated promptly.
Antimicrobial treatment
Antimicrobial levels achieved in renal tissue are generally similar to plasma concentrations, rather than the high levels achieved in renal tubules and urine. Aminoglycosides may have a unique role for treatment of pyelonephritis, as they are reabsorbed and bound in the proximal tubular epithelium, leading to higher concentrations in renal tissue than in plasma . There are few comparative clinical trials addressing treatment of acute uncomplicated pyelonephritis . Despite this, several antimicrobial regimens are clearly effective ( Box 1 ). The selection of empiric therapy is based on patient tolerance, history of prior antimicrobial therapy, and suspected or known local prevalence of resistance to E. coli .
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