L75: Urinary Tract Infections Flashcards
1
Q
Epidemiology of UTI
A
- Adult women: 25% by age 30
- Adult men: rare
- Female to male = 30:1
- 30-40%: Hospital-acquired due to use of catheters
- bacteraemia, chronic renal failure, renal stones
2
Q
Host defences in UTI
A
- Flushing effect of urine
- Humoral immunity
- Cell-mediated immunity
3
Q
Host-microbe interaction
A
- Entry
- Adhesion / Colonisation
- Spread + Multiplication
- Damage
4
Q
Microbe entry in UTI
A
Microbial factors: - Ascend from urethra - Enteric / Skin bacteria: —> E. coli (UPEC/ExPEC) —> Staphylococcus saprophyticus —> Enterococci —> Proteus mirabilis
5
Q
Host factors in microbial entry
A
- Length of urethra
- Mechanical factors (catheter, trauma)
- Genetic factors
- Hormonal effect (atrophic effect)
- Underlying disease
6
Q
Virulence factors of main uropathogens
A
- Adherence (pili, adhesin)
- Toxin
- Immune evasion (capsule, elastase)
- Iron acquisition
7
Q
UPEC / ExPEC virulence factors
A
- Type 1 and P Fimbriae
- LPS (Lipid A+ polysaccharide (O-antigen + Core))
- Capsular polysaccharide
- Toxin:
- Hemolysin
- Aerobactin
- Protease
8
Q
Microbial spread in UTI
A
- Bladder —> kidney —> blood
1. Reflux (Incompetent ureterovesical valves)
2. Poor emptying (neurogenic bladder)
3. Dilatation / Decreased peristalsis of ureter (Pregnancy)
4. Nidus for persistence (Catheter)
5. Obstruction (stones)
6. Immune incompetence (DM)
9
Q
Microbial damage in UTI
A
- Polysaccharide capsule: inhibit phagocytosis
- LPS: inflammation
- Haemolysin: tissue damage
- Urease: stone formation (urea —> NH3: precipitation of salt due to ↑ pH)
10
Q
***Uncomplicated UTI vs Complicated UTI
A
Uncomplicated UTI:
- Infection in structurally and neurologically normal UT / Health individuals
1. UPEC
2. S. saprophyticus
3. K. pneumoniae
4. Enterococcus
Complicated UTI:
- Compromised UT/ host defence / Infection in men, pregnant women, children
1. UPEC - Enterococcus
- K. pneumoniae
- Enterococcus
- Candida spp.
11
Q
***UTI syndrome
A
- Acute pyelonephritis (high fever, loin pain)
- Perinephric abscess (extension of pus through renal capsule into perinephric tissue)
- Cystitis (frequency, dysuria, suprapubic discomfort)
- Prostatitis (fever, perineal pain)
- Asymptomatic bacteriuria
- Urethritis
* ** glomerulonephritis is autoimmune (x infection)
12
Q
Recurrent, Relapse, Reinfection, Urosepsis
A
Recurrent: relapse / reinfection
Relapse: same bacterial stain, consequence of bacterial persistence
Reinfection: new infection by a different strain
Urosepsis: sepsis caused by UTI
13
Q
Microbiological diagnosis
A
- Bacteria culture (pyruria, significant bacteriuria)
—> Quantitation / Semi-quantitative culture
- differentiate contamination / genuine bacteriuria
- standard loop
- paper strip
- dip slide
- CLED agar (Cystiene, Lactose, Electrolyte Deficient agar: prevent Proteus swarming —> isolation and differentiation of urinary microbes) - Urine dipstick
—> Nitrite detection
- reduce nitrate to nitrite
- pink colour
- for Staphylococcus, Enterobacteriaceae, Proteus, Pseudomonas
- negative does not rule out: bacteria do not have the enzyme / urine not retained long enough
—> Leukocyte detection
- leukocyte esterase
- purple colour
- drugs may interfere with chemical reaction: false negative
- contamination / vaginal discharge: false positive
14
Q
Interpretation of significant bacteriuria
A
- Suprapubic tap urine: any growth
- Indwelling urine catheter: >10^5 cfu / ml plus symptoms
- Pediatric urine bag: >10^5 cfu / ml (caution)
- Clean-catch urine: >10^5 cfu / ml (caution)
- Mid-stream urine: >10^5 cfu / ml x 2 sample if no symptoms
Symptomatic patients without >10^5 cfu / ml:
- uncomplicated cystitis
- male patients
- pure growth (E. Coli) —> lower colony counts but may still be clinically significant
15
Q
Specimen collection
A
- Avoid cleaning with antiseptic (false negative)
- Whip in backward direction
False positive:
- heavy colonisation of vagina
- delayed transport
