Urinary Tract Infections : Pathogenesis & Clinical Presentations

Pathogenesis
Most Urinary Tract Infections (UTI) result when bacteria gain access to the bladder via the urethtra. some strain of bacteria (e.g. E.Coli, Proteus) are uropathogenic. These strains have virulance genes that increase the likelihood of UTI (e.g. genes encoding fimbriae that mediate attachment to uroepithelial) cells). Upper tract disease occurs when bacteria ascend from the bladder.

Women prone to infections are colonized with enteric gram-negative bacili in the periurethral urea and distal urethra prior to bacteriuria. Alterations of the normal vaginal flora (e.g. due to antibiotic treatment, other genital infections, or contraceptive use) contribute to UTIs. Other risk factors include female gender, sexual activity, pregnancy, genitourinary obstruction, neurogenic bladder dysfunction, and vesicoureteral reflux. Hematogenous infection of the kidney is less common and occurs most often in debilitated patients or in setting of staphylococcal bacteremia or candidemia.


Clinical Presentations
a. Cystitis. Patients have dysuria, frequency, urgency, and suprapubic pain. Urine is cloudy, malodorous, and sometimes bloody. Systemic signs are usually absent. Approximately one-third of patients may have silent upper tract disease.

b. Acute pyelonephritis. Symptoms develop quickly over an interval lasting from hours to a day. Patients are febrile with shaking chills can have nausea, vomiting, and diarrhea. Symptoms of cystitis may be absent. Marked tenderness may be evident on deep pressure in one or both costovertebral angles or on deep abdominal palpation.

c. Urethritis. Women with dysuria, frequency, and pyuria but no growth on bacterial urine cultures may have urethritis due to sexually transmitted pathogens such as Chlamydia trachomatis, neisseria gonorrhoea, or herpes simplex virus. Patients with hematuria, suprapubic pain, an abrupt onset of illness, an illness duration of 3 days, and a history of UTIs along with a urine culture yielding low counts of E.coli or S. saprophyticus usually have cystitis.

d. Catheter associated UTIs. Most of these infections cause minimal symptoms and no fever, they often resolve after catheter removal. Treatment without catheter removal usually fails. Bacteriuria should be ignored unless the patient develop symptoms or is at high risk for bacteremia.


17th Edition Harrison's Manual of Medicine, Section 10. Chapter 155. Urinary Tract Infections. p. 815-816

for a more detailed, see Stamm WE : Urinary Tract Infections, Pyelonephritis, and Prostatitis. Chap.282,p.1820, in HPIM-17