Urinary Tract Infection

Objectives:

  1. Outline
  2. Clinical Features
  3. Risk Factors
  4. Diagnosis
  5. Treatment
  6. Prevention
  7. Cases

What is UTI?

A urinary tract infection (UTI) is an infection in any part of your urinary system — your kidneys, ureters, bladder and urethra. Most infections involve the lower urinary tract — the bladder and the urethra. (causes: bacterial, virus)

Epidemiology

  • One of the most common infections encountered in general practice
  • Majority are uncomplicated localised infections eg. young adult women
  • Minority of cases – complicated by systemic infection and/or sepsis, increased mortality & morbidity

Complicated vs Uncomplicated
Infection associated with conditions that increases the risk of acquiring infection or failure of therapy People with no risk factors

(no structural / functional abnormalities or underlying diseases)

 

Types of Urinary Infection (location):

  1. Pyelonephritis → Kidney + Ureter
  2. Cystitis → Bladder
  3. Urethritis → Urethra
  1. Associated infections (e.g. prostatitis)

 

 

Pathogenesis (how it occurs)

  1. Ascending Infection (majority)
    1. The infection is from the lower portion of urinary tract
      1. Spread from infected anus → vagina → urethra
    2. Infection travels up the urinary tract
      1. Urethra → Bladder → Ureter → Kidney

2. Haematogenous spread

  1. Spread through the blood supplying the urinary tract

 

Clinical Features
Lower urinary tract:

  • Dysuria: painful urination
  • Urgency, frequency, “need to pee – little volume”
  • Suprapubic pain/tenderness, etc.

Upper urinary tract:

  • Flank pain, renal angle tenderness,
  • High fever (systemic infection), rigors,

Severe signs:

– Cloudy urine +/- haematuria

Systemic inflammatory response “sepsis”

(usually associated with upper UTI):

  • tachycardia, tachypnoea,
  • labile blood pressure,
  • Pyrexia (fever),
  • malaise, sweats, anorexia,
 Atypical / non-specific features of certain groups of patients:

1. Neonate/infant;

  • Can’t give history and has vague presentation (immune system weak)
  • Presents: fever, irritability

(could be meningitis)

2. Elderly patients;

  • Vague presentation as UT response is unimpressive (old)
  • General weakness / confusion

3. Immunocompromised;

  • Overlapping presentation with other infections

Complications: bacteraemia (blood); renal abscess; renal failure

Risk Factors

Uncomplicated cystitis/urethritis

(lower UTI)

Complicated UTIs
  • Female gender
    • (shorter urethra, to anus)
  • Sexual intercourse
    • Vaginal flora is disturbed
  • Use of spermicides
  • Use of diaphragm
  • Use of catheter
 Urinary tract abnormalities

(infants/children)

  • Renal malformations eg. horseshoe or duplex kidneys
  • Posterior urethral valves
  • Vesico-ureteric reflux (VUR)
  • Renal stones

Normal;

Working valves;

No back flow.

 Defective Urethral Valve

(obstruction on both ways)

– Bladder cannot empty

 Defective Ureter Valve

(can’t close)

When bladder contracts, urine flows back up ureter.

“Recycled urine” brings infections up to kidney.

 

(cont.) Risk Factors

Complicated UTIs
Urinary tract abnormalities (adults)

  • Ureteric / urethral stricture (narrowing)
  • Prostatic hypertrophy (compresses urethra)
    • → enlargement is normal as males age
  • Malignancies
  • Renal stones
Instrumentation :

 

(synthetic surfaces: bacteria may like to adhere)

Non-sterile

  • Urinary catheterisation
    • Especially for continuous use of catheter
  • Ureteric stenting , etc.
  • Neurological conditions (multiple sclerosis – nerves → bladder dysfunction)
  • Immunosuppression, diabetes, age, menopause, family history
  • Repeated antimicrobial exposure – selection of resistant uropathogens
    • I.e. drug resistant organism from vagina → UTI; harder treatment

Pregnancy

Increased risk of UTIs

  • Viginal flora (lactobaciili) is disturbed → ecoli can be introduced.. (GIT)
  • Relative state of Immunosuppression (for baby)
  • Physical Compression; by growing fetus in abdomen

Issues:

  • Clinical consequences of UTI in pregnancy
  • Asymptomatic bacteriuria
  • Drug safety
  • Recurrent infections

 

 

Aetiology

  1. Escherichia coli (main)
  2. Staphylococcus saprophyticus (pre-menopausal women)
  3. Klebsiella, Proteus, Enterobacter, etc.
What type of organisms are E. coli, Klebsiella, Proteus, Enterobacter?

Gram-negative bacilli; collectively known as Enterobacteriaceae (‘coliforms’) – also part of our normal bowel flora (spread from anus)

Others:

  • Enterococcus, Candida, staphylococci, Pseudomonas aeruginosa
  • Drug-resistant Enterobacteriaceae eg. ESBL-producing E. coli
  • Resistant to many beta-lactams (drugs) → treatment > challenging
  • Often resistant to trimethoprim
  • Often resistant to fluoroquinolones
  • May be resistant to aminoglycosides eg. gentamicin

Diagnosis

  1. Clinical
    1. Symptoms
    2. Urine dipstick / urine sample for lab
  2. Laboratory
    1. Microscopy
    2. Culture
  3. Radiological
    1. Plain radiographs (+/- contrast)
    2. Ultrasound
    3. CT/MRI
    4. Others
  4. Others eg. cystoscopy, biopsy, etc.

 

a. Clinical Diagnosis

(Getting a good urine sample)

  1. Midstream Specimen of Urine (MSU) – why midstream?
    1. As the distal urethra is usually colonised by skin bacteria; contamination
  2. Catheter Specimen of Urine (CSU) – what are the pitfalls?
    1. Catheter itself might not be sterile; contamination
  3. Others eg. blood cultures, suprapubic aspiration, bag specimen, etc.

Urinary dipstick test

Eg. leukocyte esterase (inflammatory response); nitrite (produced by bacteria)

 

Caution: Treating patients not lab results!

Do not only use the test results to treat patients;

Must correlate with history symptoms of patient

  • Do not prescribe medication without history
    • Do not treat asymptomatic UTI, as contamination is common
      • Urine collection: doesn’t/unable to follow methods
    • UTI may be able to clear with just more fluid intake
  • May be complicated UTI (presence of other conditions as well)

 

 

b. Laboratory Diagnosis

Microscopy

  • White blood cells
  • Red blood cells
  • Casts

Qualitative Culture (bacteria types)

95% of UTIs are caused by a single pathogen

  • look for ‘pure growth’ on culture
  • (specialised Agar to colour bacteria types)
  • Significant result: pure growth → ensure that sample was not contaminated
    • If not, result is useless for treatment

Pure E.coli                         Mixed Growth                         Mixed Growth

 

Quantitative Culture (number of colonies)

  • >100,000 colony-forming units (cfu)/ml urine ;
    • usually found in patient with clinical features of upper UTI (ie. pyelonephritis)
    • clinical correlation required
  • Cystitis, urethritis, complicated UTIs >1,000 – <100,000 cfu/ml urine
    • Clinical correlation is essential (ie. is patient symptomatic?)

Many cases of UTIs are associated with significant pyuria (pus)

→ Susceptibility testing with commonly used antibiotics

 

 

 

Typical Results of MSU in positive UTI

midstream specimen of urine (MSU)

  • Significant pyuria (pus)
  • Pure growth of a uropathogen
  • Significant colony count of the pathogen on culture
  • Exceptions to the above do exist:
    • Results must always be interpreted in the context of clinical features!

 

 

c. Radiological Investigations (diagnosis)

  • Plain radiographs (+/- contrast)
  • Ultrasound
  • CT/MRI
  • Others

Radiograph with contrast

Contrast is catheter-ed into bladder

  • Contrast flow is observed

→ normally, contrast should not be seen in kidney

→ this show backflow (reflux) of urine from bladder into Ureter and Kidney

→ Bladder full of contrast (normal)

 

Others (diagnosis)

Cystoscopy

  • procedure that allows your doctor to examine the lining of your bladder and urethra. A hollow tube (cystoscope) equipped with a lens is inserted into your urethra and slowly advanced into your bladder.

Biopsy

  • Tissue sample (check cellular integrity)

Treatment

Antibiotics with good penetration of urinary tract tissues:

  1. Fluoroquinolones eg. ciprofloxacin
  2. Nitrofurantoin
  3. Trimethoprim
  4. Fosfomycin
  5. Aminoglycosides eg. gentamicin IV

Reasonable penetration: Many beta-lactams (important for pregnant women)

Susceptibility Testing
From the laboratory culture, different medication is better at eradication of bacteria

  • Test for penicillin allergy (-cillins)
 Typical first-line agents:

Amoxicillin

Amoxicillin-clavulanate

Trimethoprim

Nitrofurantoin (cystitis)

Ciprofloxacin

Treatment Duration

  • Uncomplicated cystitis: 3-5 days Rx
  • Uncomplicated pyelonephritis: 7-10 days depending on choice of agents
  • Complicated UTIs: 10-14 days

 

Drug treatment in pregnancy

The choice of medication is important as drugs may be toxic to fetus (malformations)

  • Beta-lactams: generally considered safe to use
  • Trimethoprim: generally avoided in first trimester of pregnancy
  • Nitrofurantoin: avoid use at term
  • Ciprofloxacin: generally contra-indicated based on animal studies

Prevention

  1. Correction of underlying abnormalities
  2. Avoidance of unnecessary interventions
    1. eg. unnecessary antibiotics? Indication for catheterisation?
  3. Prophylaxis for recurrent UTIs
  4. Fluids (more volume to flush bacteria out)
  5. Cranberry juice (?)
    1. Cochrane review 2013 → not clinically confirmed

 

Cases

Case 1
A 25 yr-old healthy non-pregnant female presented with a 2-day history of urinary urgency and frequency, associated with fever and suprapubic pain and ‘cloudy’ urine. No back pain or renal angle tenderness.

What is the most likely diagnosis?

  • Uncomplicated UTI

MSU submitted to lab:

WCC 500 /mm3 (normal <10)

RCC 100 /mm3 (normal <10)

Pure growth of E. coli 10,000 cfu/ml

Susceptible to amoxicillin, trimethoprim & nitrofurantoin

What is your interpretation of the above result?

  • (<10,000) → Cystitis (bladder)

How would you treat the UTI?

  • Trimethoprim → fastest; ~ 3 days

Case 2
An MSU was submitted to the lab from an elderly female patient with confusion of uncertain cause. Patient is unable to give a clear history.

MSU

  • WCC 10 /mm3
  • RCC 10 /mm3
  • Mixed growth of 3 organisms >100,000 cfu/ml

Unclear presentation → Contaminated growth = Unlikely a case of UTI

Case 3
A pregnant (gestation 28/40) lady presented to antenatal clinic for routine checkup. She is otherwise well, some fatigue and mild backache. An MSU was sent to the lab as part of the routine antenatal workup.

MSU result:

  • WCC 50 /mm3
  • RCC 10 /mm3
  • Pure growth of E. coli >100,000 cfu/ml

What is your diagnosis?

Asymptomatic bacteriuria

  • Fatigue and backache are normal in a pregnant lady
  • No other UTI symptoms → asymptomatic

What is your management? And why?

Usually, asymptomatic UTI is not treated, however, since patient is pregnant (infection can cause other neonate issues) the UTI has to be treated before actual presentation. (complications)

  • Beta-lactam is the choice antibiotic even though it needs a longer course
  • As it does not affect fetus

Case 4
A 65 yr-old male had an abdominal operation 4 days ago and has a urinary catheter in situ. A CSU (catheter specimen) was sent because staff noticed that the urine looked ‘rather dark’. Patient has no specific urinary symptoms. Systemically well.

CSU results (catheter)

  • WCC 100 /mm3
  • RCC 20 /mm3
  • Pure growth of Klebsiella pneumoniae >100,000 cfu/ml
  • Susceptible to co-amoxiclav, ciprofloxacin, & resistant to trimethoprim.

What would you do? And why?

  • Dark urine: could be due to dehydration

Do not treat patient until symptomatic. (clinical presentation)

  • As the sample might have been contaminated – common
    • Especially since it is a CSU (catheter)

If patient does not need catheter (in situ) → advice to remove; if not change to new sterile one

Image result for complicated and uncomplicated uti