Microbio - UTIs Flashcards
Define bacteriuria and cystitis
Bacteriuria = presence of bacteria in the urine
Cystitis = inflammation of the bladder, often caused by infection
What is the relevance of asymptomatic bacteriuria
Asymptomatic bacteriuria is usually not relevant (due to colonisation)
It is relevant in PREGNANCY or CHILDREN
What is the difference between uncomplicated and complicated cystitis
Uncomplicated: infection is a structurally and neurologically normal urinary tract
Complicated: infection with functional or structural abnormalities (including indwelling catheters and calculi)
What is a sign that an MSU sample has not been taken properly
Squamous epithelial cells found in the urine (usually at the end of the urethra)
What factors would be regarded as a complicated UTI
Men
Pregnant women
Children (not young girls) - concerns about renal scarring or structural abnormalities
Patients in a healthcare- or HC-associated settings
What % of women will experience a symptomatic UTI at some point in life
40-50%
What is the most common causative organism for cystitis and why
Escherichia coli (O1, O2, O4, O6, O7, O8, O75, O150, O18ab)
They have adherence factors that allow prevention of flushing out by urine
Virulence factor expression is greater among the above groups → allows for more severe infection
What organisms can cause UTI
E. Coli
Staphylococcus saprophyticus (Virulence factors (P-fimbriae) that allow adherence to the epithelium)
Proteus mirabilis (kidney stones)
Klebsiella aerogenes (prosthetic materials e.g. stents, catheters)
Enterococcus faecalis
Staphylococcus epidermidis (prosthesis e.g. procedures or long-term indwelling catheter)
What are the risks of recurrent UTI
Renal scarring
Non-E. Coli organism infection e.g. Proteus, Pseudomonas, Klebsiella and Enterobacter and enterococci and staphylococci
What are the Antibacterial Host Defences in the Urinary Tract
Urine (osmolality, pH, organic acids)
Urine flow and micturition
Urinary tract mucosa (bactericidal activity, cytokines)
Why are UTIs more common in women
Female urethra is short and in proximity to the vulvar and perianal areas, making contamination likely (more common in women)
Massage of the urethra and sexual intercourse can force bacterial into the female bladder
I.E. organisms that cause UTI in women colonise the vaginal introitus and the periurethral area prior to UTI
Why can cystitis progress into pyelonephritis
Once in the bladder, bacteria multiply and pass up the ureters (especially in the presence of vesicoureteric reflux or prosthetic material) to the renal pelvis and parenchyma pyelonephritis
What are the causes of renal tract obstruction
- 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
- Extrarenal:
Describe the haematogenous route of UTI
Kidney is a frequent site of abscesses in patients with S. aureus bacteraemia or endocarditis -> excretion of Staph aureus into the urine
S. aureus does NOT have appropriate virulence factors to cause ascending infection - I.E. if you see S. aureus in the urine, it is much more likely to have come from a bacteraemia
What are the symptoms of UTI in children
<2: non-specific e.g. failure to thrive, vomiting, fever
> 2: frequency, dysuria, abdominal/flank pain
What are the symptoms of a lower UTI
Bacteria → irritation of urethral & vesical mucosa → frequent/painful urination of small amounts of turbid urine
Suprapubic heaviness or pain
Gross haematuria
Fever absent (in infections confined to lower UT)
What are the symptoms of upper UTI
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
What are the symptoms of UTI in elderly patients
Vast majority will be ASYMPTOMATIC
Symptoms of upper urinary tract infections are often atypical (e.g. abdominal pain, confusion)
Diagnosis difficult as non-infected older patients often experience frequency, dysuria, hesitancy & incontinence
What investigations should be done for suspected UTI
Urine dipstick: Nitrites (Produced by gram -ve) and Leukocyte esterase (inflammation)
MSU for urine MC&S BEFORE antibiotics administration (bottle for this contains boric acid, red top) - not useful in adults >65
Bloods – FBC, U&E, CRP
Complicated → renal USS< IV urography
What does the presence of +++ Nitrites in the urine suggest
E. Coli infection
What does nitrite -ve, LE +ve dipstick suggest
Non-coliform bacteria i.e. NOT E. coli
When should MC&S of urine be done
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
>65yo if symptomatic
What results from culture will diagnose UTI
Culture of single organisms >10^5 CFUs/mL + urinary symptoms
Culture of E. coli or S. saprophyticus organisms >10^3 CFUs/mL + urinary symptoms
What does mixed growth from culture suggest
Contamination
What should be considered in sterile pyuria (raised WCC, no growth)
Prior treatment with antibiotics (MOST COMMON)
Calculi
Catheterisation
Bladder neoplasm
TB
STI (Chlamydia trachomatis)
What do the colours pink, blue and light blue suggest on culture for UTI
Pink: E. coli
Blue: other coliforms
Light blue: gram +ve
What are the methods for urine sampling
Urine in the bladder is normally sterile. Because the urethra and periurethral areas are very difficult to sterilise, even the most carefully collected specimens (including those obtained by catheterisation) are frequently contaminated.
* MSU (best method)
* Catheterisation (may introduce organisms)
* Suprapubic aspiration (sometimes used in very young children)
What is the management of UTIs
- Send MSU before Abx
- Start empirical therapy - usually trimethoprim, nitrofurantoin, cephalexin
3 days of therapy with standard doses for treatment of uncomplicated lower urinary tract infection in women
When is short course therapy for UTI not indicated and how long should therapy be for them
History of previous urinary tract infection caused by antibiotic-resistant organisms
>7 days of symptoms
Men
7 days of treatment
What is a risk factor for canididal UTI and how is it managed
Indwelling catheter
- Remove catheter
- No treatment (unless renal transplant or waiting for surgery)
What is the difference in vulnerability to infection of different parts of the kidney
Few organisms are needed to infect the renal medulla
Many organisms are needed to infect the cortex
What is the management for pyelonephritis
Prior to culture results → amoxicillin (or ciprofloxacin)
Culture results → co-amoxiclav ± gentamicin (broad spectrums)
What are the complications of pyelonephritis
Perinephric abscess
Chronic pyelonephritis scarring, chronic renal impairment (mainly seen in children, treated more aggressively)
Septic shock
Acute papillary necrosis
