24. UTI Flashcards
What is the pathogenesis of UTI?
Why does it occur in women and men?
How does age play a role?
(4)
What are the host defences against UTI?
(4)
- Anterior urethra colonised with skin or bowel flora
- UTI increases with age & is more common in women
- Children with UTI must be followed up, as renal failure & hypertension can happen
WOMEN
- Commonest reason to see GP
- At least one UTI in lifetime
- Main reason: shorter and wider
MEN
- Less common, but increase with age and prostatic disease
- Usually underlying problem
INFLUENCE OF AGE
- Prostatic enlargement/hypertrophy
- Loss of bactericidal activity of prostatic secretions
- Faecal incontinence
- Pelvic floor muscle weakness, prolapse of uterus —> incomplete emptying of bladder
HOST DEFENCES AGAINST UTI
- Regular flow of urine
- Mucosal defense mechanisms
- pH
- Integrity of sphincter
What are the determinants of infection?
4
- Inoculum size, how many bacteria
- Virulence: ability to attach to uroepithelial cells associated with increased risk of upper UTI (some E. coli strains)
- Host Defence Mechanisms —> Innate Immunity
- Complete bladder emptying (no culture medium)
- Increase fluid intake & voiding frequency
- Vesico-ureteral valve
- Length of urethra (male>female)
- Vaginal flora: lactobacilli protective, but OCPs & spermicides decrease lactobacillary numbers & increase colonisation with aerobic GNB (E. coli) - Urinary Tract Abnormalities
- Obstruction: stones, stenosis, enlarged prostate
- Vesico-ureteric reflux (VUR): retrograde urinary flow
- Incomplete bladder emptying: provides culture medium
—> Neuropathic bladder secondary to neurological condition, DM
—> Bladder outlet obstruction —> prostatic hypertophy, urethral stricture, pelvic mass, retroperitoneal mass
- Foreign bodies: stones/calculi, stents, urinary catheters, nephrostomy tubes
What are the routes of infection?
3
- Ascending: (commonest) contamination of ano-genital region with migration of bacteria to bladder +/- renal pelvis
- Direct: fistula (vesico-colic)
- Haematogenous
What are the symptoms of UTI?
New localizing symptoms?
(6)
Systemic symptoms?
(5)
NEW LOCALIZING: point to likely site of infection
- Suprapubic pain: cystitis inflamed bladder)
- Flank pain: pyelonephritis inflamed kidney)
- Dysuria: pain when passing urine
- Frequency: passing urine every 1-2 hours
- Urgency: urge to pass urine
- Nocturia: passing of urine during night which is out of usual habit
SYSTEMIC SYMPTOMS: not specific to UTI, but can indicate complications
- Fever
- Rigors
- Acute confusional state/delerium in elderly
- Nausea, anorexia
- Obstructive uropathy may contribute to acute kidney injury and associated symptoms
What are the causative pathogens?
GNB?
(2)
Gram positive cocci?
(3)
GNB
1. Enterobacteriaceae: E. coli, K. pneumoniae, P. mirabilis, Enterobacter spp., Citrobacter spp.
- Pseudomonas aeruginosa
GRAM POSITIVE COCCI
- Staphylococci: Staphylococcus saphrophyticus
- Streptococci: Group B streptococcus also called Streptococcusagalactiae
- Enterococci: Enterococcus faecalis and Enterococcus faecium
Describe E.coli.
- Most common pathogen causing UTI = uropathogen
- Some strains of E. coli are more successful uropathogens fimbriae, poor immunogenicity
- Other Enterobacteriaceae family members that cause UTI less frequently
—> Proteus mirabilis: associated with stones/calculi – produce enzyme urease that makes urine more alkaline
Describe staphylococcus saphrophyticus.
- Coagulase negative staphylococcus —> can be part of the normal flora skin flora
- Common cause of UTI in community
- Affect young women
- Reaches bladder via ascending route
Describe enterococci.
- Another common cause of UTI
- Opportunistic pathogen and not particularly virulent
- Complicated infection in critically ill or immunocompromised patients
Describe psuedomonas aeurginosa.
- Opportunistic pathogen
- Not a common cause of UTI —> complicated infection in critically ill or immunocompromised patients or structural urinary tract abnormalities
- GNB
- Polysaccharide capsule tht anchors to epithelial cells
- Characteristic: sweet odour
- Can produce a green pigment & grows rapidly on media under aerobic conditions
What are healthcare-associated UTIs?
What are the predisposing factors?
(5)
What are the 3 likely causative organisms?
(3)
How do you prevent HCAI UTIs?
(3)
PREDISPOSING FACTORS:
1. Presence of urinary catheters
- Manipulation of the urinary tract: TRUS-guided prostate biopsy, stone fragmentation, stenting, urinary diversion – nephrostomy, ileal conduit
- Urinary stasis
- Dehydration
- Debility due to underlying disease
PATHOGENS
- Enterobacteriaceae:
- Extended spectrum beta lactamases (ESBLs)
- Carbapenemases (CRE/CPE) - Enteroccoci:
- Glycopeptide or vancomycin resistance (VRE) - Pseudomonas: already an inherently antimicrobial resistant organism
- Device-association: urinary catheters
- Complicated infection: starts as UTI, but spread to blood stream (BSI)
- Increased risk of antimicrobial resistance = fewer tx options, worse outcomes, increased costs
PREVENTION
- Standard precautions including hand hygiene – every patient, every time
- Use antibiotics appropriately and follow guidelines – reduce the risk of antimicrobial resistance
- Mind the devices:
- Don’t insert a catheter unless it’s absolutely necessary
- Review the ongoing need for the catheter daily
- Remove the catheter as soon as it is no longer required
- Insert the catheter using an aseptic technique
- Take care of the catheter while in situ and maintain a closed drainage system
How do you diagnose UTI?
(2)
What is asymptomatic bacteria? Where is it found?
What are the diagnostic tools?
(4)
DX
- Prescene of clinical symptoms
- Supporting evidence for UTI
- Common to find bacteria in urine and presence of bacteria in urine doesn’t mean UTI
Asymptomatic bacteriurim: bacteria in urine without symptoms of UTI
ASYMPTOMATIC BACTERIUM
Asymptomatic bacteriurim: bacteria in urine without symptoms of UTI
- Found in:
1. Ageing: may be found in up to 40% of older women
2. Patients with urinary catheters in situ: catheters become colonised with perineal and bowel flora within a few days of insertion
- Asymptomatic bacteriuria should not be treated in the majority of situations, but exceptions:
1. Pregnancy
2. Manipulation of the urinary tract
DIAGNOSTIC TOOLS
- Specimen of urine for testing:
A) Mid-stream urine (MSU)
- Anogenital area cleaned & labia separated
- Void first 5mls
- Collect MIDSTREAM urine into sterile container
- Get to the lab ASAP - within 2 hours of collection
- If not, refrigerate (24 – 48 hours)
B) Catheter specimen urine (CSU) if urinary catheter in situ
- Urine taken from the sampling port NOT from the drainage bag
C) Urine from a nephrostomy or ileal conduit
- Laboratory test: urine microscopy, urine culture, susceptibility testing
- Blood cultures: patient systemically unwell or sepsis need to rule out BSI
- Urinalysis / urine dipstick: near patient test (at bedside or point of care)
- Done by GP, ED, beside
- Protein, blood, glucose, ketones, leucocytes, nitrites
—> NEGATIVE for nitrites and leucocytes = UTI very unlikely
—> POSITIVE for nitrites and leucocytes = careful interpretation needed
What is the microbiology processing of urine?
(3)
What is culture and colony count? How is it interpreted?
(3)
How do you identify bacteria on agar plates?
(2)
- Microscopy: >10 WBC or pus cells in MSU
- Culture & colony count: pure growth of a uropathogen >105 = 100,000 cfu
- Antibiotic susceptibility testing
- Examine urine directly under microscope
o White blood cells (WBC) or pus cells: normally <10
o Red blood cells (RBC): calculi or glomerulonephritis, tumours or cystitis
o Epithelial cells: Presence may indicate specimen contamination
o Bacteria: visible bacteria on microscopy = bacteriuria
o Casts
CULTURE AND COLONY COUNT
- Use a 1µL = 0.001 mL sterile loop to transfer urine onto an agar plate
- Incubate overnight
- Next day, examine plate for bacterial growth count each bacterial colony = 1 bacterium: 10 colonies in 0.001ml urine = 10,000 bacteria/mL = 104/mL
- Intepretation: - > 105/mL: supports UTI diagnosis, provided patient has symptoms of UTI
- 104/mL: interpret with caution review microscopy, is the patient symptomatic, was the patient on antimicrobials before the specimen was taken?
- 103/mL: probable contamination
- Mixed growth: likely contamination, send repeat specimen only if clinically indicated
Identifying Bacteria on Agar Plate
- Chromogenic agar: presumptive identification based on colour of bacterial growth
- Automated bacterial identification
- Know the bacteria’s name, you know what antibiotics to test it against = susceptibility testing
What is the treatment for UTI?
(1)
What are the recommendations and precautions needed to take when given treatment?
(4)
What are the local antibiotic guidelines?
(5)
Tx: Antibiotics
- Don’t take a urine sample unless patient has symptoms of UTI
- Never diagnose UTI based on a positive dipstick for nitrites and leucocytes alone
- Treat the patient, not the laboratory result:
- Beware of possible of asymptomatic bacteriuria
- Almost always get a positive dipstick for nitrites and leucocytes AND a positive culture result if CSU - For uncomplicated cystitis in younger women —> delayed antimicrobial prescribing strategy may be considered
- Watch and wait, only take antibiotics if not settling or worsening within 48 – 72 hours
LOCAL ANTIBIOTIC GUIDELINES
1. Choice depends on susceptibility profile —> ensure patient has not had a history of antimicrobial resistant organisms in previous specimens
2. Narrow spectrum, if possible
- Cost: cheap, if possible (Trimethoprim, Nitrofurantoin)
- Route: usually oral (PO), IV if systemic or complicated infection
- Duration:
—> Females cystitis: 3 days
—> Males or urinary catheter in situ: 7 days
—> Complicated infection, pyelonephritis, UTI and BSI: 7 – 14 days
What is UTI and pregnancy?
What are predisposing factors of UTI in pregnancy?
(3)
What is asymptomatic bacteriuria in pregnancy?
- UTI is the commonest complication of pregnancy
- MSU routinely taken at first antenatal visit
o ~4-6% of pregnant women have asymptomatic bacteriuria
o Asymptomatic bacteriuria in pregnancy is different to other situations, because there is a significant risk it will progress to UTI and pyelonephritis
o Predisposing factors to UTI in pregnancy:
1. Decreased bladder size
2. Urethral muscle tone due to hormonal effects
3. Urinary stasis due to pressure from uterus
ASYMPTOMATIC BACTERIURIA IN PREGNANCY
- If untreated, 20-30% will develop acute pyelonephritis (AP)
- Patients with untreated bacteriuria more likely to suffer miscarriage or premature labour
- Pregnancy is one situation where antimicrobial treatment of asymptomatic bacteriuria is warranted
Can children get UTI?
What investigation is performed?
1
- Incidence 1-2%
- A/w congenital renal abnormalities (30-50%) —> vesico-ureteric reflux
- Investigations: renal U/S
