Lecture 23 - UTI Flashcards
Epidemiology of UTIs
- Neonate: male 1.5%; female 0.1%
- Children: 1-2%
- Adult women: 25% by age 30
- Adult men: rare
- Female:male = 30:1
Common UTI bacteria
- E. Coli (>80% by strains with certain virulence factors eg. UPEC or ExPEC)
- Group B strep
- Enterococcus
Factors that control the entry of bacteria into UT
- length of urethra (4cm for females, 20cm for males)
- mechanical factors
- density of bacterial receptors
- hormonal effects on mucosa
- underlying disease
Factors that control the spread of UTI
- reflux (incompetent urovesical valves)
- poor emptying (neurogenic bladder)
- dilatation and decreased peristalsis of ureter (pregnancy)
- nidus for persistance (urinary catheter)
- obstruction (stones)
- immune incompetence (DM)
Kinds of damage done by UTI
- polysaccharides: inhibit phagocytosis
- lipopolysaccharides: inflammation
- hemolysin of E. coli: tissue damage
- urease: stone formation (causes urea to turn into NH3, raises pH and therefore more precipitation)
Bacteriology
- Uncomplicated:
> in female patients without structural abnormality
> 80% E Coli, or Staph saprophyticus - Complicated:
> all male patients, patients with structural abnormality
> high likelihood of complications
> Klebsiella, Enterobacter, Pseudomonas, Serratia
Syndromes of UTI
- acute pyelonephritis
- perinephric abscess (in pts with underlying disease e.g. DM)
- cystitis (frequency, dysuria, suprapubic discomfort)
- prostatitis (acute: fever, perineal pain; chronic: non-specific, difficult to diag)
- asymptomatic bacteriuria
Microbiological diagnosis of UTI
BOTH pyuria and bacteriuria
- urinalysis (microscopy of 10WBC/mm^3 or >10WBC/high power field of 40x objective; OR strip test (detects leukocyte esterase and nitrite)
- culture of a urine specimen
Bacteriuria from urinalysis - how does it work? - what cause false negatives?
- detecting nitrite, because some bacteria (including lactose positive Enterobactericeae, Staph, Proteus, Salmonella, Pseudomonas) reduce nitrate in urine to nitrite
- positive = pink
- false negatives:
> some bacteria (e.g. enterococcus) don’t reduce nitrate
> urine may not be retained in bladder long enough for reduction to occur
Pyuria from urinalysis - how does it work? - what are the limitations?
- detecting leukocyte esterase as an indicator of leukocyte in urine
- positive = purple
- Limitations:
> false negatives: some drugs (cephalexin, high glucose levels) > false positives: contamination from vaginal discharge
Methods of quantitative/ semi-quantitative culture
- standard loop
- paper strip
- dip slide
- CLED agar to inhibit swarming by Proteus species, see colony morphology
Definition of significant bacteriuria (IMPORTANT)
- >/= 10^5 cfu per mL = significant growth
- if patient has no urinary symptoms, the same result should be obtained on >/= 2 specimens
Calculate bacterial counts with standard loop method
Positive if:
- >1000 colonies from 10ul
- multiple by volume factor (10^2), get >/= 10^5 per mL
- see growth up to 4th streak
Things that cause false results
- cleaning with antiseptic (false -)
- whip in backward direction (false +)
- heavy colonization of vagina (false +)
- delay transport of >2h (false +)
IMPORTANT concept regarding treatment of asymptomatic bacteriuria
NO SYMPTOM = NO TREATMENT
- common in debilitated elderly
- no urine culture
- no significant consequence
- does not lead to chronic nephritis, renal failure, HT, death
- select for resistant bacteria - recurrence common after treatment
Who needs treatment of asymptomatic bacteriuria?
- pregnant women (20-30% risk of progression to acute pyelonephritis)
- children <5yo when associated with vesico-ureteric reflux
- before urological operation (eg. transurethral resection of prostate)
Recurrent UTIs
- prevalence
- cause
- 1 in 10
- behavior factors, not structural abnormalities
- unusually receptive uroepithelial cells OR colonization by stick strains of E. Coli
Urological evaluation in young women
- when is it needed?
- not routine
> hematuria between infections
> pyelonephritis
> obstructive symptoms
> urea-splitting bacteria
> urinary calculi
> severe diabetes
Catheter-related UTI
- what is the risk?
- prevention methods
- 5% risk/day, 100% risk after 20-30 days
- avoid/remove/wash catheters, infection clears up after removal of catheter
Acute bacterial prostatitis - risk factors
- unprotected anal intercourse
- indwelling urinary catheter use
- prostate biopsy
Acute bacterial prostatitis - clinical presentation
- dysuria, frequency
- high fever common
- urinary retention common
- very tender prostate on rectal exam
Acute bacterial prostatitis - urine culture diag
Yields pathogen of >/= 10^5 cfu/mL
Chronic bacterial prostatitis - def, pathogens
- relapsing UTI by the same organism
- 4-/2- glass test
Pathogens:
- E Coli
- other enterobacteriaceae
- Pseudomonas aeruginosa
- Enterococci
Doubtful candidates:
- S. epidermidis
- Chlamydia trachomatis
- Mycoplasma genitalium
- Ureaplasma urealyticus
Chronic bacterial prostatitis - associated conditions
- retrograde spread of bacteria into prostatic ducts
- dysfunctional voiding
- previous instrumentation
