on 21-Sep-2023 (Thu)

标准系统。

该系统之所以称为复式簿记，是因为每笔交易都至少记录在两个不同的账户当中。每笔交易的结果至少被记录在一个借方和一个贷方的账户，且该笔交易的借贷双方总额相等，即“有借必有贷，借贷必相等”。

Bacteriuria is a frequently used term and literally means “bacteria in the urine.” The probability of the presence of infected urine in the bladder can be ascertained by quantifying the numbers of bacteria in voided urine or in urine obtained via urethral catheterization.

Significant bacteriuria is a term that has been used to describe the numbers of bacteria in voided urine that usually exceed the numbers caused by contamination from the anterior urethra (i.e., ≥105 bacteria/ mL). The implication was that in the presence of at least 105 bacteria/ mL of urine, infection must be seriously considered, and that with less than 105/mL, infection was unlikely.

The 105 criterion was of significance historically. Currently it is of value only for diagnosing asymptomatic bacteriuria, which is important to treat in only limited circumstances

Furthermore, the presence of symptoms of lower tract infection without upper tract symptoms by no means excludes upper tract infection, which may also be present

Acute pyelonephritis describes the clinical syndrome characterized by flank pain, tenderness, or both, and fever, often associated with dysuria, urgency, and frequency. However, these symptoms can occur in the absence of infection (e.g., in renal infarction or renal calculus). A more rigorous definition of acute pyelonephritis is the previously described syndrome accompanied by an indication of acute infection in the kidney.

The generally accepted definition of complicated UTI includes infection in the presence of factors that predispose to persistent or relapsing infection, such as foreign bodies (e.g., calculi, indwelling catheters or other drainage devices); obstruction; immunosuppression; renal failure; renal trans- plantation; and urinary retention from neurologic disease.1,2

In addition, infection in men, pregnant women, children, and patients who are hospitalized or in health care–associated settings may be considered complicated

Increasingly the term febrile urinary tract infection is utilized; these infections can occur with or without concomitant sepsis.3

Reinfections do not mean chronicity any more than repeated episodes of pneumonia indicate chronic pneumonia

Papillary necrosis from infection is an acute complication of pyelo- nephritis, usually in the presence of diabetes mellitus, urinary tract obstruction, sickle cell disease, or analgesic abuse. Papillary necrosis can occur in the absence of infection in some of these conditions.

The term chronic pyelonephritis means different things to different authors. To some, chronic pyelonephritis refers to pathologic changes in the kidney caused by infection only. However, identical pathologic alterations are found in several other entities, such as chronic urinary tract obstruction, analgesic nephropathy, hypokalemic nephropathy, vascular disease, and uric acid nephropathy. Pathologic descriptions do not (and cannot) differentiate between the changes produced by infection versus those produced by these other entities.

Escherichia coli is the most frequent infecting organism in initial infections.78,79 In recurrent UTIs, especially with complicated UTI (e.g., obstructive uropathy, congenital anomalies, neurogenic bladder, fistulous communication involving the urinary tract), the relative frequency of infection caused by bacteria such as Proteus, Pseudomonas, Klebsiella, and Enterobacter spp., by antibiotic-resistant E. coli, and by enterococci and staphylococci increases greatly.

More than 95% of uncomplicated UTIs are caused by a single bacterial species.

The hospital and long-term care facility environments are an important determinant of the nature of the bacterial flora in UTI. Proteus, Klebsiella, Enterobacter, and Pseudomonas spp., as well as staphylococci and enterococci, are more often isolated from inpatients, compared with a greater preponderance of E. coli in an outpatient population.80

Corynebacterium urealyticum (formerly known as Corynebacterium group D2) has been recognized as an important nosocomial pathogen.82,83 This gram-positive, urea- splitting, slow-growing bacillus may cause infected mucosal encrustations of the bladder and urinary collecting system, including struvite stones, especially in immunosuppressed patients and in particular in renal transplant recipients. It is highly resistant to antimicrobials, although usually sensitive to vancomycin. It should be considered in the presence of a high urine pH, urologic problems, previous UTI, and recent antibiotic treatment

Fungi (particularly Candida spp.) occur in patients with indwelling catheters who are receiving antimicrobial therapy.91,92

Anaerobic organisms are rarely pathogens in the urinary tract.

Coagulase-negative staphy- lococci are a common cause of UTI in some reports. Staphylococcus saprophyticus tends to cause infection in young females who are sexually active, accounting for 5% to 15% of acute cystitis episodes in the United States.93

Coagulase-positive staphylococci most often invade the kidney from the hematogenous route, resulting in intrarenal or perinephric abscesses.

Actinobaculum schaalii and other Actinobaculum spp. are facultative anaerobic gram-positive bacilli and are often missed in urine cultures because of their slow growth or dismissed as genital flora.94–96 Actinobaculum schaalii is a part of normal skin and vaginal flora. Most cases of urosepsis have occurred in patients older than 65 with renal stones undergoing lithotripsy or other instrumentation. Actinobaculum schaalii has been reported as susceptible to ampicillin, cephalosporins, and vancomycin but resistant to fluoroquinolones and TMP-SMX.

Adenoviruses (particularly type 11) have been strongly implicated as causative agents in hemorrhagic cystitis in pediatric patients (especially boys) and in allogeneic hematopoietic stem cell transplant recipients, and in UTI in renal transplant recipients.97,98

Although various investiga- tors using special media have isolated fastidious organisms from women with lower tract symptoms, the causal role of these organisms is con- troversial. Similarly, Gardnerella vaginalis, Ureaplasma urealyticum, and Mycoplasma hominis are possible but unproven causes of UTI

The methodical studies of asymptomatic bacteriuria in different populations (described later) were important in understanding the epidemiology of UTI. However, except in pregnancy, in those patients undergoing invasive genitourinary tract procedures, it is uncommonly followed by symptomatic infection and is of little consequence.

In contrast, asymptomatic bacteriuria in pregnancy (4%–7% incidence) is associated with progression to symp- tomatic pyelonephritis,103 the most common nonobstetric cause of hospitalization during pregnancy.

The problem of UTI in pediatric patients spans all age groups, beginning with neonates.104,105 The frequency of UTI in infants is about 1% to 2%. It is more common in boys during the first 3 months and thereafter occurs more often in girls.

The highest incidence of febrile UTIs occurs during the first year of life in both males and females, whereas nonfebrile UTIs (i.e., cystitis) are most common in females older than 3 years of age.

The significance of fever is that it implies renal parenchymal infection, which is associated with an increased likelihood of underlying urologic abnormalities and renal scarring.106

During the preschool years and thereafter, UTI is much more common in girls than in boys. In preschool boys, it is frequently associated with congenital urologic abnormalities.

The annual incidence of UTI in this age group is 4.5% for girls and about 0.5% for boys. Infections during this period are often symptomatic, and it is believed that much of the renal damage that occurs in association with UTI takes place in infancy and the preschool period (Fig. 72.5).112

About 7% to 8% of girls and 2% of boys have a febrile UTI during the first 8 years of life.106

In fact, antenatal ultrasound studies have demonstrated that intrinsic renal disease and not infection is the major cause of chronic renal disease in children.106

Thus the presence of bacteriuria in childhood defines a population at higher risk for the development of bacteriuria in adulthood

In general, children with UTIs without structural or functional obstruction or severe vesicoureteral reflux have a very good progno- sis.112,114

In the presence of obstruction (e.g., urethral valves), severe injury of renal parenchyma can occur.105,115 Vesicoureteral reflux is found in 30% to 50% of young children with symptomatic UTI (see Fig. 72.5).116

Reflux may be primary, which results from delayed development of the vesicoureteral junction or a short intravesical ureter, or it may occur secondary to increased pressure in the bladder due to abnormal bladder function or obstruction. Renal scarring associated with reflux is called reflux nephropathy (small scarred kidneys).

Those with reflux are more likely to develop scarring than those without reflux, and those with higher grades of reflux (grade IV or greater) are more likely to develop scar- ring than those with lower grades.118

Complications of renal scarring include hypertension and proteinuria, and end-stage renal failure may occur in some patients. Scarring has also been associated with delay in antibacterial therapy of UTI.115

It should be emphasized that the contribution of reflux alone compared with reflux plus infection in the progression of renal scarring has not been clearly delineated.

Mild to moderate degrees of reflux (and occasionally even severe reflux) are likely to disappear with time, probably in relation to maturation of the vesicoureteral junction (see “Imaging Studies” later).119 Severity (grade) of reflux is the strongest predictor of lack of resolution of reflux.121

In a multisite study of 607 children with vesicoureteral reflux, antimicrobial prophylaxis did reduce the rate of recurrence, but not scarring.

UTIs are much more common in women than in men. Premenopausal women are at especially high risk for acute cystitis; the incidence is 0.5 to 0.7 case per person-year among sexually active women. The strongest risk factors in premenopausal women include sexual intercourse, use of spermicides, and history of previous UTI, as well as diabetes. In this population, risk factors suggesting a genetic component are a history of maternal UTI and age of first UTI. Many of these patients previously had UTIs as children and continue to have infections as adults

The prevalence of asymptomatic bacteriuria in young nonpregnant women is about 1% to 3%.124 Each year, about 25% of these bacteriuric women clear their bacteriuria and an equal number become infected, often women who have had urinary infection previously. Up to 60% of the female population (5% in men) will experience at least one symptomatic UTI at some time during their life, and up to 10% of women in the United States have at least one episode of symptomatic infection each year.78

The peak incidence of symptomatic infections occurs in young, sexually active women ages 18 to 24 years, with one-third to one-half of women self-reporting at least one UTI by age 32.

Frequent sexual intercourse; a new sex partner; diaphragm use, especially with a spermicide; lack of urination after intercourse; and a history of previous infection are risk factors for urinary infection in women.78,125,127,128

The diaphragm can cause urinary obstruction in some women, but its main effect is probably a change in vaginal flora caused by the spermicide.125

About 2% to 5% of healthy women have recurrent UTIs during their lifetime.129 It seems that there may be a genetic predisposition for recurrent cystitis or pyelonephritis in these women because UTI in female relatives is strongly associated with recurrent UTI.72,129

Once a woman develops infection, she is more likely to develop subsequent infections than a patient who has had no previous infections. For example, in several studies, after a first episode of cystitis in young women caused by E. coli, 24% had a second episode within 6 months. With one or more episodes, the risk of another within 1 year was 70%.130 Recurrences after the first E. coli infection with a different uropathogen (E. coli or other) were twice as frequent as recurrences with the same E. coli strain.128 Women with acute pyelonephritis, a much less common infection than cystitis, also tended to have recur- rences.130

It may be a simple matter to cure an individual episode, but recurrence, most often reinfection, is common. The type of infection that recurs (i.e., asymptomatic bacteriuria, cystitis, or pyelonephritis) depends on a complex interaction between genetic factors and virulence characteristics of the uropathogen.131

It must be stressed that in the nonpregnant adult female with a normal urinary tract, asymptomatic bacteriuria infrequently progresses to symptomatic infection and that cystitis uncommonly progresses to pyelonephritis.

The prevalence of asymptomatic bacteriuria in adult men is low (≤0.1%), as is the occurrence of symptomatic infection, until older age, when it rises.133

Men with UTI frequently have anatomic abnor- malities of the urinary tract and therefore should be considered to have complicated UTI until proven otherwise.78 In young men, a lack of circumcision increases the risk of UTI caused by uropathogenic strains of E. coli, including the development of symptomatic urethritis.134

Male homosexuality is a risk factor, probably related to rectal insertive intercourse.135

It is clear that UTI in adults can lead to progressive renal damage in the presence of obstruction. However, recurrent infection in adults in the absence of obstruction rarely, if ever, leads to renal failure.124

One group of investigators was unable to find any case of uncomplicated pyelonephritis that progressed to end-stage renal disease among 173 patients admitted to dialysis programs.137 In prospective studies, hundreds of patients with persistent or recurrent infections in the absence of other underlying renal disease have been followed for years without documenting the progression of renal disease from infection alone

The role of infection in the progression of clinically or radiographically diagnosed interstitial renal disease has also been examined.112,124 In general, the studies indicate that infection is rarely, if ever, the major factor leading to further renal decompensation. However, infection may occasionally accelerate the progression of the primary underlying disease process.

In summary, except for perhaps rare cases, there is no evidence to indicate that uncomplicated UTI alone produces renal failure in adults.

At least 10% of men and 20% of women older than 65 years have asymptomatic bacteriuria.

reasons for the high frequency of asymptomatic bacteriuria in older patients include obstructive uropathy from the prostate (with resultant instrumentation) and loss of the bactericidal activity of prostatic secre- tions in men, poor emptying of the bladder because of prolapse in women, soiling of the perineum from fecal incontinence in demented women, and neuromuscular diseases and increased instrumentation and bladder catheter usage in both genders.139

The majority of older men with UTI have underlying urologic abnormalities.133

Urinary incontinence also contributes to UTI in postmenopausal women.140

There is a high rate of spontaneous cure and reinfection with asymptomatic bacteriuria in women and men.139

The spectrum of microorganisms is unaltered in the older adult population. Symptomatic infection uncommonly follows asymptomatic bacteriuria, and asymptomatic bacteriuria is much more frequent than symptomatic UTI in this age group.

Asymptomatic bacteriuria in older persons does not seem to have any deleterious effects.141,142 Furthermore, there is no evidence to suggest that treatment of asymptomatic bacteriuria in older patients has any beneficial effects, including decreasing urinary incontinence.142,143

Effective management of symptomatic episodes in older males requires determining whether the site of infection is the kidney, bladder, or prostate

There is a higher prevalence of asymptomatic and symptomatic UTI in hospitalized and nursing home patients than in outpatients. The general ill health of these patients and the higher probability of urinary tract instrumentation are probably the major contributors to these differences.

A single catheterization causes UTI in only about 1% of ambulatory persons. However, after a single catheterization of hospitalized patients, infection occurs in at least 10%.

Diabetics also have a higher incidence of severe infection, including severe pyelonephritis and uncommon complications such as emphysematous pyelonephritis and perinephric abscess. However, studies that followed diabetic women for up to 3 years found no advantage in screening for and treating asymptomatic UTI; it was concluded that diabetes should not be an indication for screening for or treatment of asymptomatic bacteriuria.102,149

Other conditions stated to be associated with UTI (but without documentation) include chronic potassium deficiency, gout, hypertension, and other conditions causing interstitial renal disease.

At least 50% of renal transplantation patients develop UTIs in the early postoperative period; up to 14% develop pyelonephritis, and up to 7% develop bacteremia of UTI origin in the first year.153–155 Antibacterial prophylaxis is often used in the early transplanta- tion period to prevent UTI. Recent studies have emphasized the emergence of enterococci and drug-resistant Enterobacteriaceae as posttransplantation uropathogens.156

There is a growing perspective that asymptomatic bacteriuria should not be treated because it is not generally associated with development of symptomatic disease or graft dysfunction.157

Infection in the Obstructed Kidney After Urologic Treatment of Hydronephrosis Bacteria or Candida may reach the renal pelvis through a percutaneous nephrostomy catheter or retrograde from the bladder through a ureteral stent, particularly if the catheter or stent is in place for several weeks. This colonization of the renal pelvis is generally asymptomatic unless the urine flow is obstructed. This can happen when a stent or nephrostomy tube is removed and significant ureteral stricture remains. Infection of the renal pelvis and calyces can develop rapidly, with fever and pain. Pus can fill the renal pelvis and rapidly destroy the kidney. Sometimes pus will exit the renal pelvis along a prior nephrostomy tract and form a perirenal abscess. Emergency drainage of the renal pelvis and systemic antimicrobial therapy are indicated. As a preventive measure, if there is concern about inadequate ureteral drainage after removing a stent or percutaneous nephrostomy catheter, it is useful to treat the organism in the urine just before the procedure. When Candida is in the urine, systemic fluconazole may be useful because of its high urinary concentrations.

Infections in Polycystic Kidneys Patients with autosomal-dominant polycystic kidney disease are prone to recurrent episodes of infections of their renal cysts, manifesting as fever, leukocytosis, and flank pain. Urine cultures may be negative, but bacteremia is common. Escherichia coli is the most common causative organism. Lipid-soluble antibiotics such as fluoroquinolones or TMP-SMX are thought to penetrate best into cysts. Computed tomography (CT) may show intracystic gas or a contrast-enhanced wall. Magnetic resonance imaging (MRI) is useful if renal function permits gadolinium contrast. Distinguishing infection from hemorrhage into a cyst, which is common, can be challenging. Patients not responding to antimicrobial therapy may need ultrasound-guided aspiration of infected cysts.158

Symptoms in neonates and children younger than 2 years are nonspecific.105,107,108,110 Failure to thrive, vomiting, and fever seem to be the major manifestations.

children older than 2 years (and, more consistently, older than 5 years) develop infection, they are more likely to display localizing symptoms such as frequency, dysuria, and abdominal or flank pain

The lower tract symptoms result from bacteria producing irritation of urethral and vesical mucosa, causing frequent and painful urination of small amounts of turbid urine. Patients sometimes complain of suprapubic heaviness or pain. Occasionally, the urine is grossly bloody or shows a bloody tinge at the end of micturition. Fever is generally absent with cystitis and, if present, should suggest upper tract infection. In a male, presence of fever with only symptoms of cystitis may indicate acute prostatitis.

The classic clinical manifestations of pyelonephritis include fever (sometimes with chills), flank pain, and frequently lower tract symptoms (e.g., frequency, urgency, and dysuria). At times the lower tract symptoms antedate the appearance of fever and upper tract symptoms by 1 or 2 days. It should be recognized that the symptoms described, although classic, may vary greatly.

Flank tenderness or discomfort is frequent in upper tract infection in adults and is more intense when there is obstructive disease. Severe pain with radiation into the groin is rare in acute pyelonephritis per se and suggests the presence of a renal calculus. The pain from the kidney is occasionally felt in or near the epigastrium and may radiate to one of the lower quadrants. These manifestations may offer difficulties in differential diagnosis and suggest gallbladder disease or appendicitis.

Functionally independent older adults will present with typical symptoms of UTI.159 Symptoms may not be diagnostic, however, because noninfected older patients often experience frequency, dysuria, hesitancy, and incontinence

In the very old or frail elderly, worsening of cognitive impairment, delirium, or falls may be the only presenting symptom.159 Older age is an independent risk factor for severe sepsis and septic shock in individuals with acute complicated pyelonephritis.160

Silent upper tract infection may be accompanied by lower tract symptoms only or no symptoms at all. Patients with UTIs in the presence of an indwelling urinary catheter usually have no lower tract symptoms, but flank pain or fever may occur.

Urinary tract infection is the most common source of bacteremia produced by gram-negative bacilli, which may result in the sepsis syndrome. Bacteremia may occur with no urinary symptoms, especially in the presence of an indwelling catheter

Symptoms of UTI are frequently difficult to elicit in older adults because of the presence of dementia, indwelling urinary catheters, and the atypical symptoms often seen in this population. Therefore a diagnosis of sepsis due to UTI may be made erroneously in the absence of urinary symptoms because of the presence of unrelated fever and asymptomatic bacteriuria, which is often present in this population.

Alterations in Renal Function In experimentally produced pyelonephritis, the only consistent abnormal- ity of renal function is the inability to concentrate the urine maximally.164 The mechanism of the concentrating defect is not clear but seems to be related in experimental animals to inflammation and perhaps to the increased production of prostaglandins. The concentrating defect occurs early in the course of experimental infection and is rapidly reversible with antimicrobial therapy and after the administration of prostaglandin inhibitors. The same phenomenon occurs in humans.

Progressive destruction of the kidney in the presence of obstruction may occur and give rise to clinical manifestations of renal insufficiency. Occasionally, bilateral papillary necrosis can lead to rapidly progres- sive renal failure. Acute kidney injury in the setting of pyelonephritis may occur secondary to concomitant severe sepsis (acute tubular necrosis).

Pyelonephritis in childhood, even with no evidence of compromised renal function in adolescence, has been shown to be a risk factor for renal disease in adulthood.165