Lecture 23 - UTI Flashcards
1
Q
Epidemiology of UTIs
A
- Neonate: male 1.5%; female 0.1%
- Children: 1-2%
- Adult women: 25% by age 30
- Adult men: rare
- Female:male = 30:1
2
Q
Common UTI bacteria
A
- E. Coli (>80% by strains with certain virulence factors eg. UPEC or ExPEC)
- Group B strep
- Enterococcus
3
Q
Factors that control the entry of bacteria into UT
A
- length of urethra (4cm for females, 20cm for males)
- mechanical factors
- density of bacterial receptors
- hormonal effects on mucosa
- underlying disease
4
Q
Factors that control the spread of UTI
A
- 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)
5
Q
Kinds of damage done by UTI
A
- 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)
6
Q
Bacteriology
A
- 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
7
Q
Syndromes of UTI
A
- 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
8
Q
Microbiological diagnosis of UTI
A
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
9
Q
Bacteriuria from urinalysis - how does it work? - what cause false negatives?
A
- 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
10
Q
Pyuria from urinalysis - how does it work? - what are the limitations?
A
- 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
11
Q
Methods of quantitative/ semi-quantitative culture
A
- standard loop
- paper strip
- dip slide
- CLED agar to inhibit swarming by Proteus species, see colony morphology
12
Q
Definition of significant bacteriuria (IMPORTANT)
A
- >/= 10^5 cfu per mL = significant growth
- if patient has no urinary symptoms, the same result should be obtained on >/= 2 specimens
13
Q
Calculate bacterial counts with standard loop method
A
Positive if:
- >1000 colonies from 10ul
- multiple by volume factor (10^2), get >/= 10^5 per mL
- see growth up to 4th streak
14
Q
Things that cause false results
A
- cleaning with antiseptic (false -)
- whip in backward direction (false +)
- heavy colonization of vagina (false +)
- delay transport of >2h (false +)
15
Q
IMPORTANT concept regarding treatment of asymptomatic bacteriuria
A
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
