Urinary Tract Infections Flashcards
Define bacteriuria.
Presence of bacteria in the urine.
Not always symptomatic (esp. in elderly)
Define cystitis.
Inflammation of bladder, often caused by infection.
What is an uncomplicated urinary tract infection?
Infection in a structurally + neurologically normal urinary tract.
What is a complicated urinary tract infection?
Infection in a urinary tract with functional or structural abnormalities (inc. pregnancy, indwelling catheters + calculi).
Summarise the epidemiology of UTIs.
Prevalence of bacteriuria in young nonpregnant women is 1-3%.
Up to 40% to 50% of females will experience a symptomatic UTI during their life.
What is the most common causative organism of acute UTIs? What feature allows for this?
E. Coli
Virulence factors allow them to ascend epithelium of urinary tract + evade host defences.
Other than E coli, name 5 organisms that can cause UTIs? What are they associated with?
Proteus mirabilis: affinity for those with calculi
Klebsiella aerogenes: catheterised (adhere to plastic)
Enterococcus faecalis
Staphylococcus saprophyticus: VF allow ascent, young healthy women
Staphylococcus epidermis: instrumentation, prosthetic material
What is the pathophysiology of recurrent urinary tract infections?
In recurrent UTIs esp. in presence of structural abnormalities, the relative frequency of infection caused by Proteus, Pseudomonas, Klebsiella, + Enterobacter species and by enterococci + staphylococci increases greatly.
What are antibacterial host defences in the urinary tract?
Urine: Osmolality, pH, organic acids
Urine flow + micturition: flushes out
Urinary tract mucosa: Bactericidal activity, cytokines
What is the pathophysiology of ascending UTI?
Urethra is usually colonized with bacteria.
Female urethra is short + is in proximity to warm moist vulvar + perianal areas, making contamination likely.
Organisms that cause UTI in women colonize the vaginal introitus + periurethral area before urinary infection results.
Once within the bladder, bacteria may multiply + pass up ureters, esp. if vesicoureteral reflux is present, to the renal pelvis + parenchyma
How can renal tract abnormalities contribute to UTIs?
Obstruction inhibits flushing out, resulting stasis allows bacteria to multiply + cause infection
Catheter enables ascent without VF for adherence to urinary epithelium
What are the extra renal mechanical causes of obstruction?
Valves, stenosis, or bands
Calculi
Extrinsic ureteral compression from a variety of causes e.g. gravid uterus
Benign prostatic hypertrophy
What are neurogenic malfunctions which can lead to obstruction?
Diabetic neuropathy
Spinal cord injuries
Poliomyelitis
Tabes dorsalis
How can Vesicoureteral reflux contribute to UTIs?
Perpetuates infection by maintaining a residual pool of infected urine in the bladder after voiding.
What is the haematogenous route and how does it contribute to UTIs?
Kidney is frequently the site of abscesses in patients with S. aureus bacteremia or endocarditis or both
In humans, infection of the kidney with gram -ve bacilli rarely occurs by the hematogenous route.
What are symptoms of UTIs in infants < 2y?
Nonspecific:
Failure to thrive
Vomiting
Fever
What are symptoms of UTIs in children over 2 years?
More likely to display localized Sx:
Frequency/ “accidents”
Dysuria
Abdominal or flank pain
What are symptoms of lower UTI?
Frequent + painful urination of small amounts of turbid urine.
+/- suprapubic heaviness or pain.
+/- bloody urine or shows a bloody tinge at end of micturition.
Fever usually absent in infection limited to lower tract.
What are symptoms of upper UTI?
Fever (+/- rigors)
Flank pain
+/- lower tract Sx: frequency, urgency, + dysuria
(sometimes antedate fever + upper tract Sx 1-2d)
What symptoms may present in upper tract infections in older people?
Atypical:
Abdo pain
Change in mental status: confusion, off legs
What are appropriate investigations for an uncomplicated UTI?
Urine dipstick
MSU for urine microscopy, culture + sensitivities
Bloods: FBC, UE, CRP (inflammatory markers + renal function)
How should catheterised patients with no systemic features and a positive MC+S be treated?
Nothing, bacteriuria is common in catheterised patients
What are methods of sampling?
Midstream clean catch (MSU): preferred
Catheterisation.
Suprapubic aspiration.
What is this, and what is it a sign of?
White cells pyuria
Indicative of infection
What are these fried egg cells and what is this a sign of?
Squamous epithelial cells
Indicative of contamination
What are risk factors for sterile pyuria?
Prior tx with abx
Calculi
Catheterisation
Bladder neoplasm
TB
Sexually Transmitted Disease
What is indicative of a UTI on culture?
Infection: >,10^5 cfu/mL in bladder urine, so voided urine contains >,10^5
No infection: sterile bladder urine, with proper collection, voided urine contains < 10^4
What is the treatment of UTIs in women with uncomplicated UTI and men?
Uncomplicated F: Cefalexin 3d
M: Cefalexin 7d
What are fungal infections in UTIs and what is the treatment?
Most Candida UTIs occur in catheterised
Removal of catheter may cure.
Oral fluconazole is no more effective than no therapy.
In which groups is treatment of fungal UTIs indicated?
Renal transplant patients
Patients undergoing elective urinary tract surgery.
Should attempt to eliminate/ suppress the candiduria.
What is pyelonephritis?
Infection of the Kidney.
The greater the no. organisms delivered to kidneys, the greater the chance of infection.
What is pyelonephritis commonly associated with?
Sepsis
Septicaemia
What is the management of pyelonephritis?
Requires more aggressive tx.
Broad spectrum Abx.
Co-amoxiclav +/- gentamicin.
What are 4 complications associated with pyelonephritis?
Perinephric abscess.
Chronic pyelonephritis: scarring + chronic renal impairment
Septic shock
Acute papillary necrosis
Can you prophylactically treat UTIs?
Controversial
Likely to promote resistance
Adverse effects
In which groups is bacteria in the urine worrying?
Children: may indicate structural abnormality
Pregnant: may lead to chorioamnionitis
Why is a mid-stream urine sample requested?
Flushes out commensals from urethra so they don’t contaminate the sample
In which patient groups do we consider UTIs as complicated?
Men
Pregnant women
Children
Patients hospitalised or in health-care settings (often catheterised)
Why is it important to investigate children with UTI?
May indicate structural abnormality e.g. vesicoureteric reflux which can cause scarring of the kidney + long term sequelae
A UTIs usually caused by single or multiple bacterial species?
>95% caused by single species
How do expression of different virulence factors in E coli serogroups alter manifestation of infection?
Different factors allow different level of ascent so some cause cystitis, some pyelonephritis
List 6 intrarenal mechanical causes of obstruction
Nephrocalcinosais
Uric acid nephropathy
Analgesic nephropathy
Polycystic kidney disease
Hypokalemic nephropathy
Renal lesions of sickle cell trait or disease
What may be indicated by S aureus in urine?
- Colonisation in improper sample
- S aureus bacteraemia/ endocarditis, emboli can settle in kidney, form abscess, cause excretion into the urine
Ix if systemic features e.g. fever, weight loss
How do bacteria cause symptoms in lower UTI?
Bacteria cause irritation of urethral + vesical mucosa
Why are symptoms when present in elderly often not diagnostic?
Noninfected older adults often experience frequency, dysuria, hesitancy, + incontinence.
Why should you avoid urine dipsticks for diagnosing UTI in >65s?
Less reliable
Majority have bacteruria without infection/ Sx
Abx not indicated, may cause harm e.g. C diff risk
What further investigations may be performed in a complicated UTI?
Renal USS
Intravenous urography
Why are nitrites and leukocyte esterase indicative of UTI?
Gram -ve Coliforms reduce Nitrates to Nitrites
Leukocyte esterase: sign of inflammation
Why are even carefully collected samples frequently contaminated?
Urine in bladder normally sterile
Urethra + periurethral areas v difficult to sterilise even when obtaining with catheter
What differentials should be considered to UTI?
STI
Thrush
How are men investigated differently?
Always send MSU for culture
Dipsticks are poor at excluding infection
In which 6 groups do you always send a urine culture?
>65s if symptomatic + abx given
Pregnancy
Suspected pyelonephritis/ sepsis
Men
Failed abx tx
Recurrent UTIs
What is the significance of epithelial cells in a urine sample?
Possible improper collection
Urethra: squamous
Bladder: columnar
Squamous presence indicates colonisation/ contamination
In the presence of white cells and symptoms but no organisms grown from urine what should you consider?
STIs
TB (renal TB not detected in urine cultures)
Why does a negative culture not exclude UTI?
In reality may be <10^5 bacteria/mL of urine.
In which women is short course therapy not appropriate for UTI?
Those with hx of UTI caused by Abx-resistant organisms or >7d of Sx.
Increased likelihood of upper tract infection: 7d
Which Abx are prescribed for UTI in pregnancy?
1st Trim: Nitrofurantoin
2nd + 3rd: Trimethoprim
How should UTI in catheterised patients be managed?
Remove catheter
Abx
Describe the susceptibility of the kidney itself to infection
Not uniform:
Medulla: Very few organisms needed to infect
Cortex: 10,000x as many needed
Why is imaging performed in pyelonephritis? At what threshold?
To identify Calculi or Structural cause
After 1st case: Men + Children
After 2nd case: Women
