142 - Urinary Tract Infection Flashcards
Most commonly community acquired UTI
E. coli
Are UTIs more often bacterial or viral?
Bacterial
Sex in which Proteus UTIs are more common
Males
Coagulase + Staph
Staph aureus. Coagulase - are other Staphylococci
Viral UTIs 1 2 3 4
- Usually asymptomatic shedding, e.g., CMV, rubella, polyomaviruses (JC and BK)
- May cause haemorrhagic cystitis, e.g., adenovirus
- May cause renal disease, e.g., hantavirus
- Don’t cause classical UTI
How do bacterial access the urinary tract
1
2
1) Most infections are ascending (causing cystitis, sometimes pyelonephritis)
2) Occasionally via blood (S aureus renal abscesses, Salmonella Typhi, TB)
Innate immunity in urinary tract 1 2 3 4
- Transitional epithelium resists colonisation by most types of bacteria
- Epithelium is also relatively resistant to bacterial invasion
- Some bacteria don’t like growing in urine
- Constant flushing effects of urine and regular bladder emptying play a key role in resistance to infection
Why does constant flushing of urinary tract offer resistance to bacterial infections?
Washes away enough bacteria to prevent quorum sensing.
Host factors for UTIs (in normal hosts) 1 2 3 4
1) Short urethra in females
2) Sexual intercourse
3) Colonisation of distal urethra
4) No circumcision (infant boys only)
Host factors for UTIs (in abnormal hosts)
1
2
1) Incomplete bladder emptying
2) Catheterisation
Ways in which bladder can not empty properly
1
2
- Structural abnormality (congenital, tumour, pregnancy, stone, enlarged prostate)
- Functional abnormality (neurological conditions, vesico-ureteric reflux)
Vesico-ureteric reflux
When the bladder contracts, urine is pushed both into the urethra and into the ureters, back into the kidneys.
An abnormality that predisposes to UTIs
Adhesins particularly implicated in UTIs
Type 1 pili and PAP of E. coli
Microbial factors associated with UTIs 1 2 3 4 5 6 7 8
- Adhesins, esp. type 1 pili and PAP of E. coli
- Flagella - motility
- Polysaccharide capsule, e.g., E. coli, Klebsiella
- Limited invasion - intracellular bacterial communities
- Biofilm formation (microbial communities within a matrix)
- Haemolysin, e.g., E. coli Hly associated with kidney damage
- Siderophores - for iron acquisition
- Urease, e.g., Proteus urease assists growth and promotes formation of struvite stones (NH4MgPO4·6H2O)
PAP pili
Pyelonephritis-associated pili
Example of an E. coli haemolysin gene
Hly
Example bacterium that uses urease for UTI pathogenesis
Proteus
Where do type 1 pili allow E coli to adhere?
To bladder wall
Where to PAP pili allow E coli to adhere?
To kidneys
Where is a flagellum useful in UTI infection?
In ascending the ureters
Role of siderophores
Remove iron from transferrin. Have a higher affinity for iron than transferrin
Unusual formation of E coli in UTIs
Can form filaments of bacteria
Diagnosis of UTIs 1 2 3 4
- History and physical examination (Difficult to distinguish lower from upper UTI)
- Imaging – ultrasound, radiology for structural and functional abnormalities
- Collect appropriate samples – urine (and blood)
- Interpret lab reports
Presenting problems with UTIs
Pain on micturition
High frequency of urination
Urgency of urination
Types of urine samples 1 2 3 4
- Per urethra: midstream urine (MSU)
- Catheter/nephrostomy sample
- Bag sample (in babies)
- Suprapubic aspirate (used in paediatrics)
Most-common type of urine sample
Midstream sample
How are catheter samples taken?
Only if a catheter is already in, or is being inserted for another reason.
Catheters can introduce other pathogens, so could make things worse
Why are suprapubic aspirates used in children?
Hard to get a good urine sample from a child.
Only time that bad samples are useful
In excluding a UTI.
If detect pathogens, doesn’t really tell you anything about where they came from
How is urine collected from a catheter?
Don’t take from bag, as urine might have been sitting for a while, so bacteria could be replicating, and would give unrepresentative results.
Take from junction between catheter and collecting tube
Things that are looked for in lab examinations of urine samples
•
Microscopy for: WBC, RBC, epithelial cells, casts, crystals, microorganisms incl. parasitic forms
•Count WBC and RBC
•Quantitative culture for bacteria
•Susceptibility testing of isolates
•Some micro labs also perform chemical analyses
Example of a worm that infects bladder
Schistosoma
Normal WBC in urine
Under 10^4 per mL.
Over 10^5 in infection, with stones, tumours, etc
Normal RBC in urine
Under 10^4 per mL
Normal squamous epithelial cells in urine
0.
Presence suggests poorly-collected sample
Normal CFU in a quantitative culture for bacteria
Under 10^3 CFU/mL.
Over 10^5 CFU/mL strongly suggestive of infection (especially if only one species is isolated)
Number of CFU taken to be significant from a catheter sample of urine
Over 10^2 CFU/mL
Number of CFU taken to be significant from a suprapubic aspirate
Any growth is significant
Why must urine sample be delivered to a lab very quickly?
Because rely on quantitative sample.
If takes too long, bacteria can replicate, which makes results unrepresentative.
Try to get to a lab in under an hour
Sterile pyuria
Pus in the urine without bacterial growth. Causes include: • Non-infectious conditions • Partial treatment • Difficult to grow bacteria, e.g., TB
What can cause burning sensation when urinating?
Acid in urine from colonising bacteria
Antimicrobials recommended for uncomplicated cystitis 1 2 3 4
Trimethoprim or Cephalexin or Co-amoxyclav or Nitrofurantoin 5 days for women and children 7 days for men
Antimicrobials recommended for pyelonephritis 1 2 3 4
Co-amoxyclav or
Cephalexin or
Trimethoprim
for 10-14 days.
If severe sepsis use ampicillin/amoxycillon + gentamycin
Asymptomatic bacteriuria
1
2
3
- Repeated >105 CFU/ml without symptoms
- No significance except in pregnancy
- Treat with cephalexin OR co-amoxyclav OR other
What is defined as a recurrent UTI in women?
> 2 UTIs in 6 months
Most common cause of recurrent UTIs in women?
Mostly reinfections, not relapses.
What should you do if a recurrent UTI is a relapse? 1 2 3 4 5 6 7 8
- If relapse, check for urinary tract abnormality
- Caused by:
- genetic predisposition
- behaviour: intercourse, spermicide, incontinence, etc.
- Management
- change behaviour; ↑ fluid intake; postcoital voiding
- antimicrobial prophylaxis (different regimes)
