142 - Urinary Tract Infection

Question 1

Most commonly community acquired UTI

Answer 1

E. coli

Question 2

Are UTIs more often bacterial or viral?

Answer 2

Bacterial

Question 3

Sex in which Proteus UTIs are more common

Answer 3

Males

Question 4

Coagulase + Staph

Answer 4

Staph aureus. Coagulase - are other Staphylococci

Question 5

Viral UTIs
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2
3
4

Answer 5

• 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

Question 6

How do bacterial access the urinary tract
1
2

Answer 6

1) Most infections are ascending (causing cystitis, sometimes pyelonephritis)
2) Occasionally via blood (S aureus renal abscesses, Salmonella Typhi, TB)

Question 7

Innate immunity in urinary tract
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Answer 7

• 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

Question 8

Why does constant flushing of urinary tract offer resistance to bacterial infections?

Answer 8

Washes away enough bacteria to prevent quorum sensing.

Question 9

Host factors for UTIs (in normal hosts)
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3
4

Answer 9

1) Short urethra in females
2) Sexual intercourse
3) Colonisation of distal urethra
4) No circumcision (infant boys only)

Question 10

Host factors for UTIs (in abnormal hosts)
1
2

Answer 10

1) Incomplete bladder emptying

2) Catheterisation

Question 11

Ways in which bladder can not empty properly
1
2

Answer 11

• Structural abnormality (congenital, tumour, pregnancy, stone, enlarged prostate)
• Functional abnormality (neurological conditions, vesico-ureteric reflux)

Question 12

Vesico-ureteric reflux

Answer 12

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

Question 13

Adhesins particularly implicated in UTIs

Answer 13

Type 1 pili and PAP of E. coli

Question 14

Microbial factors associated with UTIs
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8

Answer 14

• 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)

Question 15

PAP pili

Answer 15

Pyelonephritis-associated pili

Question 16

Example of an E. coli haemolysin gene

Answer 16

Hly

Question 17

Example bacterium that uses urease for UTI pathogenesis

Answer 17

Proteus

Question 18

Where do type 1 pili allow E coli to adhere?

Answer 18

To bladder wall

Question 19

Where to PAP pili allow E coli to adhere?

Answer 19

To kidneys

Question 20

Where is a flagellum useful in UTI infection?

Answer 20

In ascending the ureters

Question 21

Role of siderophores

Answer 21

Remove iron from transferrin. Have a higher affinity for iron than transferrin

Question 22

Unusual formation of E coli in UTIs

Answer 22

Can form filaments of bacteria

Question 23

Diagnosis of UTIs
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3
4

Answer 23

• 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

Question 24

Presenting problems with UTIs

Answer 24

Pain on micturition
High frequency of urination
Urgency of urination

Question 25

Types of urine samples 
1
2
3
4

Answer 25

• Per urethra: midstream urine (MSU)
• Catheter/nephrostomy sample
• Bag sample (in babies)
• Suprapubic aspirate (used in paediatrics)

Question 26

Most-common type of urine sample

Answer 26

Midstream sample

Question 27

How are catheter samples taken?

Answer 27

Only if a catheter is already in, or is being inserted for another reason.
Catheters can introduce other pathogens, so could make things worse

Question 28

Why are suprapubic aspirates used in children?

Answer 28

Hard to get a good urine sample from a child.

Question 29

Only time that bad samples are useful

Answer 29

In excluding a UTI.

If detect pathogens, doesn’t really tell you anything about where they came from

Question 30

How is urine collected from a catheter?

Answer 30

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

Question 31

Things that are looked for in lab examinations of urine samples

Answer 31

•
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

Question 32

Example of a worm that infects bladder

Answer 32

Schistosoma

Question 33

Normal WBC in urine

Answer 33

Under 10^4 per mL.

Over 10^5 in infection, with stones, tumours, etc

Question 34

Normal RBC in urine

Answer 34

Under 10^4 per mL

Question 35

Normal squamous epithelial cells in urine

Answer 35

0.

Presence suggests poorly-collected sample

Question 36

Normal CFU in a quantitative culture for bacteria

Answer 36

Under 10^3 CFU/mL.

Over 10^5 CFU/mL strongly suggestive of infection (especially if only one species is isolated)

Question 37

Number of CFU taken to be significant from a catheter sample of urine

Answer 37

Over 10^2 CFU/mL

Question 38

Number of CFU taken to be significant from a suprapubic aspirate

Answer 38

Any growth is significant

Question 39

Why must urine sample be delivered to a lab very quickly?

Answer 39

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

Question 40

Sterile pyuria

Answer 40

Pus in the urine without bacterial growth.
Causes include:
• Non-infectious conditions
• Partial treatment
• Difficult to grow bacteria, e.g., TB

Question 41

What can cause burning sensation when urinating?

Answer 41

Acid in urine from colonising bacteria

Question 42

Antimicrobials recommended for uncomplicated cystitis 
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2
3
4

Answer 42

Trimethoprim or 
Cephalexin or 
Co-amoxyclav or 
Nitrofurantoin 
5 days for women and children
7 days for men

Question 43

Antimicrobials recommended for pyelonephritis 
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2
3
4

Answer 43

Co-amoxyclav or
Cephalexin or
Trimethoprim
for 10-14 days.

If severe sepsis use ampicillin/amoxycillon + gentamycin

Question 44

Asymptomatic bacteriuria
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2
3

Answer 44

• Repeated >105 CFU/ml without symptoms
• No significance except in pregnancy
• Treat with cephalexin OR co-amoxyclav OR other

Question 45

What is defined as a recurrent UTI in women?

Answer 45

> 2 UTIs in 6 months

Question 46

Most common cause of recurrent UTIs in women?

Answer 46

Mostly reinfections, not relapses.

Question 47

What should you do if a recurrent UTI is a relapse?
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Answer 47

• 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)