UTI is an inflammatory response of the urothelium to bacterial invasion that is usually associated with bacteriuria and pyuria.
Bacteriuria is the presence of bacteria in the urine.
Pyuria, the presence of white blood cells (WBCs) in the urine, is generally indicative of infection and/or an inflammatory response of the urothelium to bacteria, stones, an indwelling foreign body, or other conditions that can contribute to pyuria.
Bacteriuria without pyuria is generally indicative of bacterial colonization without overt infection of the urinary tract. Pyuria without bacteriuria, or sterile pyuria, warrants further evaluation (see the discussion of pyuria in the section on urinalysis).
Cystitis describes a clinical syndrome of dysuria, frequency, urgency, and occasionally suprapubic pain.
Acute pyelonephritis is a clinical syndrome of chills, fever, and flank pain that is accompanied by bacteriuria and pyuria, a combination that is reasonably specific for an acute bacterial infection of the kidney.
Chronic pyelonephritis describes a shrunken, fibrosed kidney, diagnosed by morphologic, radiologic, or functional evidence of renal disease that may be postinfectious but is frequently not associated with current (active) UTI.
UTIs may also be described in terms of the anatomic or functional status of the urinary tract and the health of the host. Uncomplicated describes an infection in a healthy patient with a structurally and functionally normal urinary tract; this often specifically refers to the absence of obstruction to any part of the urinary tract.
A complicated infection is associated with factors that increase the chance of acquiring bacteria and decrease the efficacy of therapy. The urinary tract is structurally or functionally abnormal, the host is compromised, and/or the bacteria have increased virulence or antimicrobial resistance.
Factors That Suggest a Complicated Urinary Tract
Infection
Functional or anatomic abnormality of urinary tract
Male gender
Pregnancy
Elderly patient
Diabetes
Immunosuppression
Childhood urinary tract infection
Recent antimicrobial agent use
Indwelling urinary catheter
Urinary tract instrumentation
Hospital-acquired infection
Symptoms for more than 7 days at presentation
Infection
Functional or anatomic abnormality of urinary tract
Male gender
Pregnancy
Elderly patient
Diabetes
Immunosuppression
Childhood urinary tract infection
Recent antimicrobial agent use
Indwelling urinary catheter
Urinary tract instrumentation
Hospital-acquired infection
Symptoms for more than 7 days at presentation
UTIs may also be defined by their relationship to
other UTIs:
• A first or isolated infection is one
that occurs in an individual who has never had a UTI or has one remote
infection from a previous UTI.
• An unresolved infection is one that has
not responded to antimicrobial therapy and is documented to be the same
organism with a similar resistance profile.
• A recurrent infection is
one that occurs after documented, successful resolution of an antecedent
infection. Consider these two different types of recurrent infection:
1. Reinfection describes a new event associated
with reintroduction of bacteria into the urinary tract.
2. Bacterial persistence refers to a recurrent
UTI caused by the same bacteria reemerging from a focus within the urinary tract,
such as an infectious stone or the prostate. Relapse is frequently used
interchangeably. These definitions require careful clinical and bacteriologic
assessment and are important because they influence the type and extent of
the patient's evaluation and treatment.
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The sequelae of complicated UTIs are substantial. It is well established in the presence of obstruction, infection stones, diabetes mellitus, and other risk factors that UTIs in adults can lead to progressive renal damage. The long-term effects of uncomplicated recurrent UTIs are not completely known, but, so far, no association between recurrent infections and renal scarring, hypertension, or progressive renal azotemia has been established.
• UTIs are the most common bacterial infection and, as such, make a significant impact on health care costs.
• The incidence of bacteriuria increases with institutionalization/hospitalization as well as with pregnancy and certain comorbidities that alter lower urinary tract function or cause immunosuppression.
• No clear association has been described between recurrent uncomplicated UTIs and renal sequelae such as scarring, hypertension, or progressive renal insufficiency.
• UTIs are the most common bacterial infection and, as such, make a significant impact on health care costs.
• The incidence of bacteriuria increases with institutionalization/hospitalization as well as with pregnancy and certain comorbidities that alter lower urinary tract function or cause immunosuppression.
• No clear association has been described between recurrent uncomplicated UTIs and renal sequelae such as scarring, hypertension, or progressive renal insufficiency.
Pathogenesis:
UTIs occur as a result of interactions between the uropathogen and the host. Successful infection of the urinary tract is determined in part by the virulence factors of the bacteria, the inoculum size, and the inadequacy of host defense mechanisms.
Routes of Infection
Ascending Route
Most bacteria enter the urinary tract from the bowel and skin reservoir via ascent through the urethra into the bladder. Adherence of pathogens to the introital and urothelial mucosa plays a significant role in ascending infections.
Most episodes of pyelonephritis are caused by retrograde ascent of bacteria from the bladder through the ureter to the renal pelvis and parenchyma. Although reflux of urine is probably not required for ascending infections, edema associated with cystitis may cause sufficient changes in the ureterovesical junction to permit reflux. Once the bacteria are introduced into the ureter, they may ascend to the kidney unaided. However, this ascent would be greatly increased by any process that interferes with the normal ureteral peristaltic function. Gram-negative bacteria and their endotoxins, as well as pregnancy, ureteral obstruction, and high lower tract pressures have a significant antiperistaltic effect.
Bacteria that reach the renal pelvis can enter the renal parenchyma by means of the collecting ducts at the papillary tips and then ascend upward within the collecting tubules.
Hematogenous Route
Infection of the kidney by the hematogenous route is uncommon in normal individuals. However, the kidney is occasionally secondarily infected in patients with Staphylococcus aureus bacteremia originating from oral sites or with Candida fungemia. Experimental data indicate that infection is enhanced when the kidney is obstructed.
Lymphatic Route
Direct extension of bacteria from the adjacent organs via lymphatics may occur in unusual circumstances, such as a severe bowel infection or retroperitoneal abscesses. There is little evidence that lymphatic routes play a significant role in the majority of UTIs.
UTIs occur as a result of interactions between the uropathogen and the host. Successful infection of the urinary tract is determined in part by the virulence factors of the bacteria, the inoculum size, and the inadequacy of host defense mechanisms.
Routes of Infection
Ascending Route
Most bacteria enter the urinary tract from the bowel and skin reservoir via ascent through the urethra into the bladder. Adherence of pathogens to the introital and urothelial mucosa plays a significant role in ascending infections.
Most episodes of pyelonephritis are caused by retrograde ascent of bacteria from the bladder through the ureter to the renal pelvis and parenchyma. Although reflux of urine is probably not required for ascending infections, edema associated with cystitis may cause sufficient changes in the ureterovesical junction to permit reflux. Once the bacteria are introduced into the ureter, they may ascend to the kidney unaided. However, this ascent would be greatly increased by any process that interferes with the normal ureteral peristaltic function. Gram-negative bacteria and their endotoxins, as well as pregnancy, ureteral obstruction, and high lower tract pressures have a significant antiperistaltic effect.
Bacteria that reach the renal pelvis can enter the renal parenchyma by means of the collecting ducts at the papillary tips and then ascend upward within the collecting tubules.
Hematogenous Route
Infection of the kidney by the hematogenous route is uncommon in normal individuals. However, the kidney is occasionally secondarily infected in patients with Staphylococcus aureus bacteremia originating from oral sites or with Candida fungemia. Experimental data indicate that infection is enhanced when the kidney is obstructed.
Lymphatic Route
Direct extension of bacteria from the adjacent organs via lymphatics may occur in unusual circumstances, such as a severe bowel infection or retroperitoneal abscesses. There is little evidence that lymphatic routes play a significant role in the majority of UTIs.
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