WHAT ARE URINARY TRACT INFECTIONS?
- 1WHAT IS THE MEANING OF URINARY TRACT INFECTIONS?
- Infections of the urinary tract represent a wide variety of clinical syndromes, including urethritis, cystitis, prostatitis, and pyelonephritis.
- A urinary tract infection (UTI) is defined as the presence of microorganisms in the urine that cannot be accounted for by contamination. The organisms have the potential to invade the tissues of the urinary tract and adjacent structures.
- Lower tract infections include cystitis (bladder), urethritis (urethra), prostatitis (prostate gland), and epididymitis. Upper tract infections involve the kidney and are referred to as pyelonephritis.
- Uncomplicated UTIs are not associated with structural or neurologic abnormalities that may interfere with the normal flow of urine or the voiding mechanism. Complicated UTIs are the result of a predisposing lesion of the urinary tract, such as a congenital abnormality or distortion of the urinary tract, stone, indwelling catheter, prostatic hypertrophy, obstruction, or neurologic deficit that interferes with the normal flow of urine and urinary tract defences.
- Recurrent UTIs, two or more UTIs occurring within 6 months or three or more within 1 year, is characterised by multiple symptomatic episodes with asymptomatic periods occurring between these episodes. These infections are due to reinfection or relapse. Reinfections are caused by a different organism and account for the majority of recurrent UTIs. Relapse represents the development of repeated infections caused by the same initial organism.
- 2WHAT ARE THE CAUSES OF URINARY TRACT INFECTIONS?
- The most common cause of uncomplicated UTIs is Escherichia coli, accounting for more than 80% to 90% of community-acquired infections. Additional causative organisms are Staphylococcus saprophyticus, Klebsiella pneumonia, Proteus spp., Pseudomonas aeruginosa, and Enterococcus spp.
- The urinary pathogens in complicated or nosocomial infections may include E. coli, which accounts for less than 50% of these infections, Proteus spp., K. pneumoniae, Enterobacter spp., P. aeruginosa, staphylococci, and enterococci. Enterococci represent the second most frequently isolated organisms in hospitalised patients.
- Most UTIs are caused by a single organism; however, in patients with stones, indwelling urinary catheters, or chronic renal abscesses, multiple organisms may be isolated.
- 3WHAT ARE THE SIGNS AND SYMPTOMS OF URINARY TRACT INFECTIONS?
- The typical symptoms of lower and upper UTIs are presented in Table1– 1.
- Symptoms alone are unreliable for the diagnosis of bacterial UTIs. The key to the diagnosis of a UTI is the ability to demonstrate significant numbers of microorganisms present in an appropriate urine specimen to distinguish contamination from infection.
- Elderly patients frequently do not experience specific urinary symptoms, but they will present with altered mental status, change in eating habits, or gastrointestinal (GI) symptoms.
A standard urinalysis should be obtained in the initial assessment of a patient. Microscopic examination of the urine should be performed by preparation of a Gram stain of unspun or centrifuged urine. The presence of at least one organism per oil-immersion field in a properly collected uncentrifuged specimen correlates with greater than 100,000 colony- forming units (CFU)/mL (105 CFU/mL) (>108 CFU/L) of urine.
- Criteria for defining significant bacteriuria are listed in Table1–2.
(CFU, colony-forming unit.)
- The presence of pyuria (>10 white blood cells/mm3 [10 × 106/L]) in a symptomatic patient correlates with significant bacteriuria. A count of 5 to 10 WBC/mm3 (5 × 106 to 10 × 106/L) is accepted as the upper limit of normal.
- The nitrite test can be used to detect the presence of nitrate-reducing bacteria in the urine (e.g., E. coli). The leukocyte esterase test is a rapid dipstick test to detect pyuria.
- The most reliable method of diagnosing UTIs is by quantitative urine culture. Patients with infection usually have more than 105 bacteria/mL [108/L] of urine, although as many as one-third of women with the symptomatic infection have less than 105 bacteria/mL [108/L].