Urinary Tract Infections

Definitions

Urinary Tract Infections (UTI) –  are caused by the presence of bacteria in the urine (bacteriuria), which is normally free of bacteria.

Pyuria - The presence of white blood cells (WBC’s) in the urine, indicative of an inflammatory response to bacterial invasion.

Acute Pyelonephritis - is a clinical syndrome of chills, fever, and flank pain that is accompanied by bacteriuria and pyuria, indicating an acute infection of the kidney.

Chronic Pyelonephritisdescribes a shrunken, scarred kidney, secondary to recurrent inflammatory insults over various periods of time.

Cystitis is inflammation of the bladder, whether bacterial or otherwise. Bacterial cystitis as opposed to nonbacterial cystitis can be a useful differentiating term.

Urethritisthis refers to inflammation in the urethra, rather than the bladder. Symptoms from one are very difficult to differentiate from the other. Pure urethritis in the female – unlike that in the male – is very rare.

Recurrent Infections are due to either reinfection with a new organism after an infection-free period, or to bacterial persistence or recurrence caused by the same organism from a persistent focus within the urinary tract.

Most Common Causes of Persistent UTI

  • The infective organism is resistant to the antibiotic selected
  • The development of resistance in a previously susceptible organism
  • Poor renal function, which prevents antibiotic concentration in the urine
  • The presence of stones or abnormal tissue leading to high concentrations of bacteria
  • Urinary reflux
  • Predisposing genetic factors that increase chance of bacterial attachment to host
  • Chronic bacterial prostatitis (infection of the prostate)
  • Foreign bodies
  • Urethral diverticula and infected urethral glands
  • Fistulas to the bladder from colon or other infectious collections

Routes of InfectionMost bacteria enter the urinary tract from the fecal reservoir in a retrograde manner, via ascent through the urethra into the bladder.

Bacterial Adherence and ColonizationStudies have demonstrated that for infection to occur bacteria have to adhere to host tissue and this is done through hair-like protein appendages on bacteria called pili, which adhere to receptor sites on cells. The virulence of bacteria depends on the strength of this interaction, which is affected by both bacterial and host factors and maybe genetically determined.

Principles of Antimicrobial Therapy

Initial Elimination of BacteriaElimination of bacteria occurs within hours if the proper antimicrobial agent is used.

Duration of TherapyIn women with uncomplicated UTI’s, 3 days of full-dose therapy has been shown to be as effective as longer courses. In the presence of mitigating circumstances, such as recurrence, chronicity, age older than 65, diabetes or pregnancy, a 7-day regimen should be considered. In complicated infections, or infections of the kidney, 14- to 21-day regimens should be used.

Asymptomatic Bacteriuria (the presence of bacteria in the urine)Older people frequently have this condition, without the symptoms of a UTI. This condition does not require treatment in the absence of symptoms. Treating these patients only clears their urine of bacteria for short periods and then they become recolonized. Multiple treatments lead to the development of resistant organisms.

Factors Increasing Severity of Infection

  • Urinary obstruction
  • Renal or bladder stones
  • Catheter drainage
  • Diabetes
  • Spinal cord injury or neurogenic bladders
  • Pregnancy
  • Acute bacterial prostatitis (prostate infections)

Bladder Infections

Uncomplicated Cystitisclinical symptoms include dysuria (burning), frequency, urgency, voiding of small volumes, or sensation to void without much urine, and suprapubic and lower abdominal pain. The presumptive diagnosis can be made on urinalysis, but urine culture remains the definitive test. Short course of antibiotic therapy adequate in women with uncomplicated infections, but should be avoided in men.

Reinfectionscause has to be identified and corrected. Specific risk factors have been identified for reinfections in women, including the first UTI before age of 15 years and maternal history of UTI’s. In women, diaphragm-spermicide and tampon use have been associated with increase risk of UTI and vaginal colonization with E. coli bacteria. Spermicides containing the active ingredient nonoxynol-9 may provide a selective advantage in reducing colonization. Thus, spermicidal agents should be discontinued in women with recurrent UTI’s.

Postmenopausal women have frequent reinfections. Estrogen replacement frequently restores the normal vaginal environment.

Low-Dose Prophylaxislong term, low-dose therapy can be given to prevent reinfection. The success of prophylactic therapy depends on the effect of the antimicrobial agent on the vaginal and fecal reservoirs of pathogenic bacteria. One a day dosing for 6 weeks is a common regimen. In some cases 6-12 months are needed.

Post-Intercourse Prophylaxissexual activity has been established as an important risk factor for acute cystitis in women. Post-intercourse therapy with antimicrobials in women with “honeymoon cystitis” taken as a single dose post intercourse reduces the rate of infection.

Urinary Tract Infections During Pregnancybecause pregnant women with bacteriuria are at an increased risk to develop kidney infections, this should be looked for and treated when found. Selection of an antibiotic to treat the bacteriuria must be made with special consideration to maternal and fetal toxicity.

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