Urinary tract infection

• Important questions in infection medicine

  • Who- populations at risk
  • What- responsible organism
  • Why- pathogenesis
  • Where- local or systemic, source/seed
• Urinary tract anatomy

  • Upper - made of kidneys and ureters, infection here is called pyelonephritis
  • Lower - made of bladder and urethra, infection here is called cystitis
• Risk factors for uncomplicated UTIs

  • Female
  • Previous UTIs
  • Sexually active
  • Vaginal infection
  • Diabetes
  • Obesity
  • Genetic susceptibility
  • Older age (oestrogen deficiency, cognitive impairment)
• Broadly similar risk factors between cystitis and pyelonephritis
• Factors that compromise the urinary tract or host defence leading to complicated UTIs:

  • Urinary obstruction (e.g., prolapse, prostatic enlargement)
  • Urinary retention caused by neurological disease
  • Immunosuppression
  • Renal failure
  • Renal transplant
  • Pregnancy
  • Presence of foreign bodies (e.g., indwelling catheters (CAUTI) or other drainage devices)
• CAUTI are most common cause of secondary blood stream infection
• Organisms causing uncomplicated UTIs

  • 75% E.coli
  • 6% K. pneumoniae
  • 6% S. saprophyticus
  • 5% enterococcus spp.
• Organisms causing complicated UTIs

  • 65% E. coli
  • 8% K. pneumoniae
  • 11% enterococcus spp.
• Bacterial virulence factors

  • Adherence - pili, adhesins
  • Toxin production - e.g., haemolysins
  • Immune invasion - e.g., capsule
  • Iron acquisition
  • Other - flagella
• Host Antibacterial defences:

  • urine (extremes of osmolality, low pH and high urea concentration inhibit bacterial growth)
  • urine flow and micturition
  • urinary tract mucosa (bactericidal activity, cytokines)
  • urinary inhibitors of bacterial adherence (Tamm-Horsfall protein),
  • inflammatory response
• Locations of UTI

  • Urethritis
  • Prostatitis
  • Epididymo-ochiditis
  • Cystitis
  • Pyelonephritis
• Sources of UTI

  • Uropathogen from gut
  • Intracellular bacterial communities/quiescent intracellular reservoirs
  • Haematogenous - rare
• Seeding of UTI

  • Bacteraemia common in pyelonephritis
  • Perinephric abscesses
  • Can rarely lead to remote deep seated infection
• Clinical presentations of upper UTI

  • Loin pain/flank tenderness, fever/rigors, sepsis
• Clinical presentations of lower UTI

  • Dysuria (pain when passing urine), frequency, urgency, suprapubic tenderness
• Clinical presentations in infants (<2 yrs)

  • Vomiting /fever
• Clinical presentations in elderly

  • Less localised symptoms - confusion/falls
• Dipstick test

  Only to be used in patients <65, because of the presence of asymptomatic bacteria in the elderly population which are just present and not causing issues. Useful only in presence of clinical UTI symptoms- presence of nitrites indicate a UTI is a possible diagnosis. as low as 75% sensitivity
• Types of urine samples for culture

  • Mid stream urine
  • Clean catch urine
  • Catheter sample urine CSU- from port not bag
  • Other - urostomy/cystoscopy/pad
• Significant bacteriuria

  Indicates that the number of bacteria in the voided urine exceed the number expected from contamination from the anterior urethra
• Asymptomatic bacteriuria

  Significant bacteriuria in a patient without symptoms (only ever treated in pregnant women)
• Culture results support clinical diagnosis only
• Scenarios requiring alternative antibiotic guidance

  • Signs of sepsis follow: upper UTI/pyelonephritis and sepsis 6
  • Symptoms of pyelonephritis
  • Lower UTI in pregnancy
  • If you are unsure of the source of infection follow : sepsis of unknown causes
• Recommended total antibiotic duration

  Women-3 days, Men-7 days
• Antibiotic recommendation if no risk factors for trimethoprim resistance

  Trimethoprim 200mg every 12 hours
• Antibiotic recommendation if risk factors for trimethoprim resistance and eGFR>30

  Nitrofurantoin 100mg every 12 hours
• Purpose of antibiotics for cystitis

  Improving and shortening of symptom duration, not curing
• Trimethoprim decreases cystitis symptom duration by 4 days
• Subgroup of patients that should be managed without Antibiotics for cystitis

  • Ibuprofen users
  • 25% culture negative patients
• Ibuprofen more effective as a treatment in culture negative cystitis groups
• Antimicrobial use increases risk of recurrent UTI
• Antimicrobial use increases antimicrobial resistance
• Factors determining antibiotic choice:

  • Do they need antibiotics
  • Dependent on clinical syndrome (where)
  • What is resistance risk
  • Oral vs intravenous
• Nitrofurantoin is for cystitis only
• 60-70% E.coli resistance to amoxicillin and 30% resistance to trimethoprim
• Factors determining oral vs intravenous antibiotics

  • Are there signs of systemic inflammatory responce (SIRS) or sepsis
  • Some multi drug resistant organisms only have IV choices available
• Required investigations for upper UTI management

  • Blood cultures
  • Urine cultures (preferably mid stream specimen or catheter specimen if catheterised)
  • Review the last three urine cultures up to 12 months ago
• Contact microbiology if a gentamicin resistant organism has been isolated
• Recommended antibiotics for upper UTI

  • Gentamicin (use NHS Lothian calculator)
  • Consider adding amoxicillin (1g every 8 hours IV) where enterococcus has been isolated in urine in the last 12 months or source of infection is unclear or if the patient has signs of severe sepsis
• Recommended antibiotics for upper UTI with penicillin allergy

  • Gentamicin
  • Consider adding vancomycin (NHS Lothian guidelines) where enterococcus has been isolated in urine in the last 12 months or source of infection is unclear or if the patient has signs of severe sepsis