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Micbi > Urinary Tract Infections > Flashcards

Urinary Tract Infections Flashcards

1
Q

Is urinary tract sterile?

A

Yes except distal 1/3 (from urethra)

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2
Q

Is any bacteria detected in voided urine significant?

A

Voided urine always has urethral flora

- Significant only if >10^5 CFU/mL in mid stream urine

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3
Q

Is there a threshold for significant bacteriuria in supra-pubic urine?

A

NO - any growth is significant!!

upper urinary tract is sterile

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4
Q

Prevalence of UTI: female vs male

A

Female: risk increases with age

Male: lower risk than female (longer urethra) except paediatrics (uncircumcised foreskin)

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5
Q

Lower UTI: Clinical features of urethritis, cystitis, prostatitis

A

Generally: storage symptoms (frequency, urgency) + others

Urethritis
- Dysuria, Urethral discharge

Cystitis
- Dysuria, suprapubic pain, haematuria

Prostatitis

  • cystitis symptoms
  • obstructive symptoms e.g. hesitancy, poor-stream, post-micturition dribbling, perineal/ low back pain
  • complicated by epididymitis
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6
Q

Upper UTI: Clinical features of pyelonephritis

A

Ureter and kidney
- pyelonephritis = inflammation of renal parenchyma

Fever, loin pain, tender renal angle, bacteraemia

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7
Q

UTI in different populations: uncomplicated, complicated and paediatrics

A

Uncomplicated UTI
- adult, non-pregnant female, no structural/ neurological dysfunction
== GOOD PROGNOSIS

Complicated UTI

  • male or pregnant female
  • further investigations required (for any underlying structural abnormality)
  • lower cure rate, higher recurrence

UTI in paediatrics

  • boys>girls
  • prolonged fever of unknown origin, febrile convulsion, failure to thrive
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8
Q

Pathogenesis: Routes of infection

A

Ascending

  • shorter urethra in female
  • indwelling catheters
  • vesicoureteric reflux

Haematogenous/ Descending

  • pre-existing bacteraemia e.g. s. aureus, MTB
  • -> pyelonephritis and renal abscess
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9
Q

Pathogenesis: Microbial factors

A

Uropathogenic E.coli
- production of K (capsular) antigen, adherence to uroepithelial cell by fimbriae/ adhesins

Many other organisms can also cause UTI

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10
Q

Pathogenesis: Host factors - normal defence, risk factors

A

Urinary tract normally resistant

  • regular mechanical flushing via micturition
  • phagocytosis by polymorphs
  • humoral Ab (IgA)
  • urine is hyperosmolar, high urea and low pH

Risk factors:

  • incomplete emptying/ stasis (extra-/intra-luminal and luminal defects)
  • vesicoureteric reflux (anatomic defect of submucosal tunnel in children)
  • instrumentation (damage uroepithelium)
  • abnormal constituents e.g. DM glucose
  • female
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11
Q

Causative organisms (2 main classes, others)

A

Gram negative bacilli

  • E. coli 75%
  • Klebsiella
  • Proteus (raise pH by splitting urea; struvite and apatite stone forming)
  • Pseudomonas – catheterised patients

Gram positive cocci

  • S. aureus (bacteraemia, endocarditis)
  • Coagulase negative staph (elderly male with outflow obstruction)
  • s. saprophytic (sexually active young women)
  • enterococcus

Others (only if immunocompromised)

  • anaerobes, mycobacteria, STD
  • candida (catheterised)
  • virus e.g. adenovirus
  • parasites - schistosoma haematobium
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12
Q

Diagnosis: Specimen

A

First pass urine

  • not sterile
  • removed to minimise urethral flora EXCEPT GONOCOCCAL/CHLAMYDIA urethritis

Midstream urine

  • mainly from bladder
  • need careful cleansing of labia or glans
  • quantitative culture for significant growth threshold

Terminal urine
- useful if suspect prostatitis

Catheterised urine

  • catheterised or uncooperative patients
  • prone to contamination with biofilm formation
  • “fresh catheterised urine” or collect from sampling port
  • NOT FROM DRAINAGE BAG (always contaminated)

Suprapubic urine

  • paediatric: bladder is supra-pubic and palpable, can’t cooperate
  • elderly male: AROU (>1L urine = palpable)
  • aspiration using aseptic technique
  • any growth is significant

Transport of specimen should be in sterile container (with boric acid; lasts 24-48 hrs) immediately – prevent overgrowth

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13
Q

Diagnosis: enzymatic methods

A

Urine multistix

  • useful screening
  • can’t differentiate between contamination and infection
  • nitrite test: reductase from enterobacteriaceae convert nitrite to nitrate
  • leukocyte test: esterase from WBC
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14
Q

Diagnosis: microscopy

A

80 microL of urine in microtitre plate, inverted microscope

  • unstained wet mount
  • WBC, dysmorphic RBC, bacteria, yeast, cast
  • gram stain not performed: contaminated
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15
Q

Diagnosis: culture

A

Dip-slide

  • MacConkey on one side and CLED (cysteine-lactose-electrolyte- deficient) on another side
  • immediate inoculation and culture
  • can’t perform microscopy

Filter paper strip method (rare now)

  • standard volume of urine taken up by filter paper and impregnated onto agar plate with CLED medium
  • back calculation after overnight incubation (significant if >10^5 CFU/mL)

Standard (calibrated) loop method - MC

  • similar to filter paper strip but use 1 microL or 10 microL standard loop
  • spread between 4 quadrants
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16
Q

Diagnosis: identification and sensitivity

A

Biochemical methods mostly
Proteinomics and genomics if can’t identify

Antibiotic susceptibility testing

17
Q

Interpretations of negative culture

A 
Genuine absence of UTI
Prior use of antibiotics
Diuresis (dilution)
Fastidious organisms e.g. STD
TB infection (sterile pyuria -- repeat with early morning urine)
18
Q

Treatment: non-pharmacological

A

Increase fluid intake
Good personal hygiene
Correct underlying disease

19
Q

Treatment: pharmacological

A

Antibiotics that concentrate in the urine:
Urinary tract agents
- Nitrofurantoin
- Fosfomycin

Cephalosporins (resistance), Quinolones (side effects), BLBLI (augmentin empirically used), aminoglycosides

Duration:

  • 3 days in uncomplicated case
  • 5-7 days otherwise
  • up to 90% cure

recurrence/ failure of treatment prompts further investigation for underlying reason

20
Q

Treatment: Cystitis

A

PO: Nitrofurantoin, Augmentin
(also septrin, fosfomycin for ESBL)

Nitrofurantoin empirically used in uncomplicated cystitis
- caution in elderly: avoid if CrCl <30 ml/min

DO NOT use fluoroquinolone in uncomplicated cystitis unless no other options

  • serious side effects e.g. tendinopathy, aortic dissection, arrhythmia, CNS
  • only useful in prostatitis (high conc at prostate)
21
Q

Treatment: Acute Pyelonephritis

A

IV: Augmentin
IV Tazocin if suspect pseudomonas or carbapenem in severe/rapid deteriorating cases

Duration:
- IV until afebrile for 24-48 hrs then complete 14 days with oral drugs

22
Q

UTI in children: prognosis, management

A

Non-specific symptoms
Prognosis: renal scarring

Management: thorough Ix for structural abnormality, consider long term prophylactic antibiotics

23
Q

UTI pregnancy: prognosis, management

A

around 5% occurrence
- 25 % develop pyelonephritis if untreated
==> COMPLICATED PREGNANCY: low birth weight, prematurity if early infection; foetal loss, neonatal sepsis if late

Management:
- INDICATION form antibiotic treatment even if asymptomatic

Micbi (32 decks)

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