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Pathophysiology of urinary tract infection • Ascending route of infection is the most common. • Hospital infection associated with lower urinary tract instrumentation (catheterization, cystoscopy). • Once in the bladder uropathogens multiply, then pass up the ureters to the renal pelvis and parenchyma • Source of uropathogens: enteric bacteria mainly Urinary tract infection more common in women than men • Short female urethra. • Close proximity to perianal areas. • Men also have an antibacterial substance in their prostate gland that reduces their risk. Pathophysiology of urinary tract infection • • • • • • • Cystitis: (lower urinary tract infection) Pyelonephritis: infection of the kidney with acute suppurative inflammation of the pelvis, medullary and cortical tubules, corticomedullary intersititum Urosepsis: bacteremia due to pyelonephritis Papillary necrosis Sloughing of necrotic pyramids Perinephric abscess Risk factors in complicated urinary tract infection • • • • • • • • Indwelling catheters Urinary calculi Neurogenic bladder Prostatic enlargement Uterine prolapse Urologic instrumentation or surgery Renal transplantation Diabetes mellitus Common uropathogens • • • • • • • • Escherichia coli Other Enterobacteriaceae (Klebsiella, Enterobacter, Proteus, Citrobacter) Pseudomonas aeruginosa Enterococcus Staphylococcus saprophyticus Staphylococcus aureus • Associated with staphylococcemia Streptococcus agalactiae (group B) • Denotes vaginal colonization in pregnant women Candida Uncommon uropathogens • Corynebacterium urealyticum • Haemophilus influenzae and H. parainfluenzae • Blastomyces dermatitidis • Neisseria gonorrhaeae • Mycobacterium tuberculosis Notes • Adult urine volume = 600 – 2500 ml /24hr. • Oligouria: marked decrease in urine flow < 400 ml/24hr. • Polyuria: Marked increase in urine flow > 2500 ml/24hr. • Anuria: less than 100 ml/24hr. • Nocturia: excessive urination during night. • Aim of the test An etiological diagnosis of bacterial urinary tract infection by quantitative Cultivation of the urine with identification and susceptibility test of the isolated bacteria(s). • Criteria of specimen rejection Un-refrigerated specimen older than 2 hours may be subject to overgrowth unlabeled specimen; mislabeled specimen; Specimen in expired transport container Types of urine specimens • First-voided morning urine optimal (generally bacteria have been proliferating in bladder urine for several hours) • Midstream urine specimens (initially voided urine contains urethral commensals) • Indwelling catheters (freshly placed, urine aspirated by needle inserted into catheter) (Foley catheter tips not acceptable) • Straight catheter specimens • Suprapubic aspirates (infants or children, recovery of anaerobes) • Cystoscopic collection of urine Specimen collection • Male: 1. 2. 3. • If not circumcised, draw back the foreskin. Begin to urinate, but pass the first portion into the toilet. Collect the mid-portion of urine into the container, and pass the excess into the toilet. Female: 1. 2. 3. Squat over the toilet and separate the labia with one hand. Void the first portion of urine into the toilet. Collect the mid-portion of urine into the container and pass the excess into the toilet. Collection of urine specimens • Urine collected in sterile specimen container must be processed within hours, or refrigerated and processed within 24 hours • Urine collected in sterile specimen container with borate preservative should be processed within 24 hours (no refrigeration required) Catheterized urine • Cleanse periurethral area with soap and water • Insert catheter into bladder Discard initial urine Collect specimen in sterile cup • Chronic indwelling Foley catheter Clamp tubing below junction (or port) Disinfect with alcohol Insert needle (on syringe) through port or catheter wall and aspirate. • DO NOT recontamination Suprapubic aspiration Inoculation of urine • Inoculation of urine for quantitative culture (colony forming units→ CFU’s) performed with a calibrated 0.001 mL(1µL) and 0.01 mL (10µL) plastic or wire loop • Nutrient agar or sheep blood agar utilized for quantitative urine culture • With 0.001 ml loop, 1 colony on SBA equivalent to 1,000 CFU’s per mL of urine • With 0.01 ml loop, 1 colony on SBA equivalent to 100 CFU’s per mL of urine • MacConkey agar utilized as selective differential agar for gram-negative bacteria Count plate Interpretation: Clean Voided Specimen • • • Normal: <10,000 organisms per ml. Organisms >10,000 per ml needs repeat urine culture? Urinary Tract Infection Boys • Organisms >10,000 per ml suggests UTI likely Girls • Organisms >100,000 per ml suggests UTI • • • Three specimens: 95% probability of UTI Two specimens: 90% probability of UTI One specimen: 80% probability of UTI Post specimen processing • Interfering factors: • Patient on antibiotic therapy. • Improper sample collection. • Result reporting: • Report wet mount as an initial report. • Report the isolated pathogen and its sensitivity pattern as a final report. • Turn around time: • Wet mount results should be available 1 hour after specimen receipt. • culture will be reported out 1-2 days after the receipt of the specimen. • Isolation of a possible pathogen can be expected after 2-3 days Negative