Urinary Tract Infections Flashcards
Is urinary tract sterile?
Yes except distal 1/3 (from urethra)
Is any bacteria detected in voided urine significant?
Voided urine always has urethral flora
- Significant only if >10^5 CFU/mL in mid stream urine
Is there a threshold for significant bacteriuria in supra-pubic urine?
NO - any growth is significant!!
upper urinary tract is sterile
Prevalence of UTI: female vs male
Female: risk increases with age
Male: lower risk than female (longer urethra) except paediatrics (uncircumcised foreskin)
Lower UTI: Clinical features of urethritis, cystitis, prostatitis
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
Upper UTI: Clinical features of pyelonephritis
Ureter and kidney
- pyelonephritis = inflammation of renal parenchyma
Fever, loin pain, tender renal angle, bacteraemia
UTI in different populations: uncomplicated, complicated and paediatrics
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
Pathogenesis: Routes of infection
Ascending
- shorter urethra in female
- indwelling catheters
- vesicoureteric reflux
Haematogenous/ Descending
- pre-existing bacteraemia e.g. s. aureus, MTB
- -> pyelonephritis and renal abscess
Pathogenesis: Microbial factors
Uropathogenic E.coli
- production of K (capsular) antigen, adherence to uroepithelial cell by fimbriae/ adhesins
Many other organisms can also cause UTI
Pathogenesis: Host factors - normal defence, risk factors
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
Causative organisms (2 main classes, others)
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
Diagnosis: Specimen
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
Diagnosis: enzymatic methods
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
Diagnosis: microscopy
80 microL of urine in microtitre plate, inverted microscope
- unstained wet mount
- WBC, dysmorphic RBC, bacteria, yeast, cast
- gram stain not performed: contaminated
Diagnosis: culture
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
Diagnosis: identification and sensitivity
Biochemical methods mostly
Proteinomics and genomics if can’t identify
Antibiotic susceptibility testing
Interpretations of negative culture
Genuine absence of UTI Prior use of antibiotics Diuresis (dilution) Fastidious organisms e.g. STD TB infection (sterile pyuria -- repeat with early morning urine)
Treatment: non-pharmacological
Increase fluid intake
Good personal hygiene
Correct underlying disease
Treatment: pharmacological
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
Treatment: Cystitis
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)
Treatment: Acute Pyelonephritis
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
UTI in children: prognosis, management
Non-specific symptoms
Prognosis: renal scarring
Management: thorough Ix for structural abnormality, consider long term prophylactic antibiotics
UTI pregnancy: prognosis, management
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
