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a path 3 > MICRO: Urinary Tract Infections > Flashcards

MICRO: Urinary Tract Infections Flashcards

1
Q

Is the urethra sterile?

A

No - many colonising organisms, some asymptomatic infections can also occur in the elderly

This is why we ask patients to take a mid-stream sample to flush out the urethra initially

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2
Q

What cells should you not find in an MSU?

A

Squamous epithelial cells are found at the end of the urethra

If squamous epithelial cells are found in an MSU sample, the sample has not been taken properly

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3
Q

Define bacteruria and cystitis.

A

Bacteriuria: presence of bacteria in the urine. Asymptomatic bacteriuria is NOT usually relevant. However, asymptomatic bacteriuria with coliform is significant in PREGNANCY

Cystitis: inflammation of the bladder, often caused by infection AKA: Lower UTI

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4
Q

What is the classification of cystitis?

A

​Uncomplicated: infection is a structurally and neurologically normal urinary tract

Complicated: infection with functional or structural abnormalities (including indwelling catheters and calculi)

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5
Q

In which patients is a UTI regarded as complicated?

A
  • Men
  • Pregnant women
  • Children (not young girls)
  • Patients in healthcare (or associated) settings
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6
Q

How common is UTI?

A

Prevalence of bacteriuria in young non-pregnant women: 1-3%

40-50% of female population will experience a symptomatic UTI at some point during their life

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7
Q

What % of UTI are caused by more than one bacterium? Which organism is most common and why?

A

Only ~5%

Over 95% of UTIs are caused by a single bacterial species

Most Common = Escherichia coli (in acute infection); particular serogroups:

  • Many virulence factors which allow them to survive and ascent in the UT
  • O1, O2, O4, O6, O7, O8, O75, O150, O18ab - main serogroups
  • These E. coli have adherence factors that allow it to prevent being flushed out by the passage of urine
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8
Q

Other than E coli, what organisms cause UTI?

A
  • Proteus mirabilis
  • Klebsiella aerogenes
  • Enterococcus faecalis
  • Staphylococcus saprophyticus (coagulase -ve staphylococcus)
    • 2nd most common cause of UTI in younger women
    • Virulence factors (P-fimbriae) that allow adherence to the epithelium
  • Staphylococcus epidermidis
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9
Q

What UTI is staph epidermidis associated with?

A

UTI in the presence of prosthesis (e.g. procedures or long-term indwelling catheter)

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10
Q

What is proteus mirabalis associated with in general?

A

Kidney stones

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11
Q

What UTI is Staphylococcus saprophyticus (coagulase -ve staphylococcus) associated with?

A
  • 2nd most common cause of UTI in younger women
  • Virulence factors (P-fimbriae) that allow adherence to the epithelium
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12
Q

What happens with recurrent UTI in terms of organisms?

A

Recurrent UTI may mean structural abnormalities

–> relative frequency of infection caused by non-E. coli organisms to increase greatly (e.g. Proteus, Pseudomonas, Klebsiella and Enterobacter and enterococci and staphylococci)

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13
Q

Name 3 antibacterial host defences present in the urinary tract.

A
  • Urine (osmolality, pH, organic acids)
  • Urine flow and micturition
  • Urinary tract mucosa (bactericidal activity, cytokines)
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14
Q

Why are women more at risk of UTI?

A

Female urethra is short and in proximity to the vulvar and perianal areas, making contamination likely

I.E. organisms that cause UTI in women colonise the vaginal introitus and the periurethral area

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15
Q

What can occur once the bacteria are in the bladder?

A

Once in the bladder, bacteria multiply and pass up the ureters (especially in the presence of vesicoureteric reflux) to the renal pelvis and parenchyma –> pyelonephritis

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16
Q

How does BPH or other obstruction increase risk of UTI?

A

Obstruction inhibits flow of urine –> stasis of urine –> increasing susceptibility to infection

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17
Q

What are the causes of obstruction of the urinary tract?(10)

A
  • Mechanical
  • Extrarenal:
    • Valves, stenosis or bands
    • Calculi
    • BPH
  • Intrarenal
    • Nephrocalcinosis
    • Uric acid nephropathy
    • Analgesic nephropathy
    • PKD
    • Hypokalaemic nephropathy
    • Renal lesions of SCD
  • Neurogenic malfunction:
    • Poliomyelitis
    • Tabes dorsalis
    • Diabetic neuropathy
    • Spinal cord injuries
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18
Q

How does vesicoureteric reflux increase risk of UTI?

A

Perpetuate infection by maintaining a residual pool of infected urine in the bladder after voiding

The reflux can result in scarring of the kidneys

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19
Q

Which bacteria commonly causes UTI via the haematogenous route? What are some associaeted features?

A
  • SUSPECT ABSCESS in kidney if S. aureus found in urine especially with previous bacteraemia or endocarditis
  • …. because S. aureus does NOT have appropriate virulence factors to cause ascending infection

  • Infection of the kidney with Gram-negative bacilli rarely occurs by the haematogenous route*
  • I.E. if you see S. aureus in the urine, it is much more likely to have come from a bacteraemia*
  • whereas E. coli in the urine is much more likely to be due to ascending infection*
20
Q

Which gram infection is more likely to cause haematogenous route of UTI?

A
  • Gram +ve
  • Infection of the kidney with Gram-negative bacilli rarely occurs by the haematogenous route
21
Q

What are the symptoms of UTI in children (<2years and >2years)?

A

Children <2 years (inc. neonates) à symptoms are NON-SPECIFIC:

  • Failure to thrive
  • Vomiting
  • Fever

Children >2 years à localised symptoms:

  • Frequency
  • Dysuria
  • Abdominal or flank pain
22
Q

What are LUTI symptoms?

A

Bacteria –> irritation of urethral & vesical mucosa –> frequent/painful urination of small amounts of turbid urine

  • Suprapubic heaviness or pain
  • Gross haematuria
  • Fever absent
23
Q

What are the UUTI symptoms?

A
  • Lower UT symptoms / LUTS [frequency, urgency, nocturia, dysuria**] /**FUND HIPS
    • May precede UUTS by 1-2 days
    • Symptoms may vary greatly
  • Fever (sometimes with rigors)
  • Flank pain
24
Q

What are the symptoms of UTI in older patients?

A

Vast majority ASYMPTOMATIC

Diagnosis difficult as non-infected older patients often experience frequency, dysuria, hesitancy & incontinence

Often atypical symptoms of UUTI (e.g. abdominal pain, confusion)

25
Q

What is the problem with urine dipsticks in >65yo?

A

Often asympotomatic bacteria present in those >65 especially with urinary catheters

Doing dipstick which will be positive and will then be treated –> selects resistant organisms which will be difficult to treat later

The key is not to over-treat

There are guidelines for this

26
Q

What investigations are used for uncomplicated and complicated UTI?

A

Uncomplicated:

  • Urine dipstick
  • MSU for urine MC&S
  • Bloods – FBC, U&E, CRP

Complicated: (In sexually active young men, consider chlamydia trachomatis)

  • Renal USS
  • IV urography
27
Q

What is the outcome for each of these?

A
28
Q

If there are many squamous epithelial cells in a bacterium containing sample, ewhat should you do?

A

Interpret with caution as this is unlikely to be a mid stream sample and so more likely to be contaminated

29
Q

First picture - white cells

Second picture - urethral contamination as shows some faint squamous epithelial cells

A
30
Q

What is the short diagnostic criteria in terms of organisms for UTI?

A

Culture of single organisms >105 CFUs/mL + urinary symptoms

= diagnostic of UTI

OR

Culture of E. coli or S. saprophyticus organisms >103 CFUs/mL + urinary symptoms = diagnostic of UTI

Symptomatic and asymptomatic infections may have <103 CFUs/mL so interpret with clinical picture

31
Q

What white cell number shows inflammation in UTI?

A

White cells >104/mL (or 107/L) = inflammation

Pyuria is usually ABSENT in children

32
Q

Give some reasons for a sterile pyuria.

A

Sterile pyuria (raised WCC but no growth on culture), consider:

  • Prior treatment with antibiotics (MOST COMMON)
  • Calculi
  • Catheterisation
  • Bladder neoplasm
  • TB
  • STI (Chlamydia trachomatis)
33
Q

What are the laboratory tests for UTI? What type of agar is used for culture?

A
  • Microscopy
  • Culture (chromogenic agar – turns different colours based on growth)
    • Pink = E. coli
    • Blue = other coliforms
    • Light blue = gram +ve
  • Sensitivities - still used as no other way of doing this yet
34
Q

Name 3 types of urine samples.

A
  • MSU (best method)
  • Catheterisation (may introduce organisms)
  • Suprapubic aspiration (sometimes used in very young children)
35
Q

How do you treat UTI in females? When are 7 days of treatment used?

A

3 days of therapy with standard doses for treatment of uncomplicated lower urinary tract infection in women

  • 7 days of treatment if:
    • History of previous urinary tract infection caused by antibiotic-resistant organisms
    • >7 days of symptoms
    • In all men

Because increased risk of UUTI ^

36
Q

What is the management of fungal UTI?

A

Most Candida UTIs occur in patients with indwelling catheters - most cases of candiduria are due to vaginal thrush rather than infection of UT

Management:

  1. Removal of the catheter (antifungals no more effective than no therapy)
  2. No benefit treating asymptomatic infection
  • Exceptions (attempts should be made to eliminate or suppress candiduria):
    • Renal transplant patients
    • Patients who are waiting to undergo elective urinary tract surgery
37
Q

What is the empirical therapy for most uncomplicated UTI (classical presentation)?

A
  • Guided by local policies;
  • Normally Trimethoprim/Nitrofurantoin/Cephalexin for uncomplicated UTIs
  • No nitrofurantoin in pregnancy as associated with haemolysis
38
Q

Are ESBL producing organisms treated inpatient or outpatient?

A

Using OPAT OPAT (outpatient parenteral antimicrobial therapy)

39
Q
A

Nitrites

40
Q

When must MC&S laboratory testing be done?

A
  • Pregnancy (because asymptomatic bacteriuria is an issue)
  • Suspected UTI in children
  • Suspected UTI in men
  • Suspected pyelonephritis
  • Catheterised patients
  • Failed antibiotic treatment (resistance)
  • Abnormalities of the genitourinary tract
  • Renal impairment

Important as gives better clinical picture and prevents unnecessary treatment which may cause SE such as thrush.

41
Q

When should imaging be done in UTI?

A
  • Killing normal bacteria by giving unnecessary antibiotics for UTI may result in thrush (yeasts are not affected by ABx)
42
Q

What are the risk factors for pyelonephritis pathology?

A

Greater number of organisms delivered to kidney

43
Q

Is the kidney unifromy susceptible to infection? (i.e. its different parts)

A

The kidney is not uniformly susceptible to infection—very few organisms are needed to infect the medulla, whereas x10,000 are needed to infect the cortex

44
Q

What is the treatment for pyelonephritis?

A

Co-amoxiclav +/- gentamicin

45
Q

What are the complications of pyelonephritis?

A

Perinephric abscess

Chronic pyelonephritis

  • scarring
  • chronic renal impairment

Septic shock

Acute papillary necrosis

a path 3 (89 decks)

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