• 30% of females have symptomatic UTI by age 24 ^[4]
• 50% of females will have at least one UTI during their lifetime ^[4]
• UTI is the most common nosocomial infection worldwide, largely driven by catheter-associated UTI (CAUTI)
• In Hong Kong, UTI is a leading cause of bacteraemia in elderly patients, particularly in residential care homes

Demographics: F >>> M (rare in M except at extremes of age: 0–1 year or > 60 years with BPH). Bacteriuria is 30× more common in young females than males. Incidence increases with age, with a sharp increase after onset of sexual activity. ^[4]

• Ageing population: Hong Kong has one of the highest proportions of elderly globally → high burden of complicated UTI, CAUTI, and UTI-related bacteraemia
• Antimicrobial resistance: Hong Kong outpatient urinary E. coli isolates show high resistance to ampicillin (64–67%), levofloxacin (36–46%), and co-trimoxazole (31–32%), but low resistance to nitrofurantoin (1–2%) and fosfomycin (~2%). This is why empirical cystitis treatment locally favours nitrofurantoin or amoxicillin-clavulanate over fluoroquinolones/co-trimoxazole.
• DM prevalence: ~10% of HK adults have DM → increased UTI risk (impaired immunity, glycosuria, neurogenic bladder, diabetic cystopathy)

Why are females more susceptible? The shorter female urethra means bacteria need to travel a much shorter distance to reach the bladder. The close proximity of the urethral meatus to the vaginal introitus and anus creates a "highway" for faecal flora to colonise the periurethral area and ascend.

Bacterial virulence: characteristics of uropathogens that allow them to colonise and invade the urinary tract. ^[1]

Can be divided into:

• Factors against external agents, e.g. antimicrobial resistance ^[1]
• Factors against the host ^[1]

Virulence Factors Against the Host (Focus on UPEC)

This is the overwhelmingly commonest route:

1. Colonisation of periurethral area by uropathogenic enteric pathogen
   (usually from faecal flora, especially E. coli)
                    ↓
2. Bacterial ascent through the urethra into the bladder
   (facilitated by short female urethra, sexual intercourse, catheterisation)
                    ↓
3. Attachment to uroepithelial cells via active receptor-mediated process
   - Mediated by glycosphingolipid receptors on epithelial cell surface
   - Type 1 pili (FimH) bind to uroplakin Ia on umbrella cells
                    ↓
4. Toll-like receptor (TLR) activation
   - Bacterial attachment recruits TLRs (transmembrane co-receptors)
   - TLR4 recognises LPS → triggers cytokine cascade (IL-6, IL-8, TNF-α)
   - Generates local inflammatory response → PMN recruitment → pyuria
                    ↓
5. Bacterial proliferation in bladder → CYSTITIS
   (if host defences overwhelmed or impaired)
                    ↓
6. ± Ascent into ureters and kidney → PYELONEPHRITIS
   - Bacteria with P-pili adhere to upper tract urothelium
   - Facilitated by VUR, ureteral obstruction, or catheterisation
                    ↓
7. ± Invasion into bloodstream → UROSEPSIS
   (if renal parenchymal barrier breached)

Understanding why UTI produces specific symptoms connects directly to the inflammatory response:

• Dysuria (painful urination): Inflammation of the bladder/urethral mucosa → exposure of sensory nerve endings to inflammatory mediators + urine acidity
• Frequency and urgency: Inflamed bladder wall has ↓compliance and ↑irritability → the detrusor muscle contracts at lower volumes → premature sense of fullness
• Suprapubic pain: Peritoneal irritation from inflamed bladder dome (the dome is covered by peritoneum)
• Haematuria: Mucosal inflammation → capillary damage → blood in urine
• Fever: Systemic response to infection — more prominent in upper tract infection where bacteria have access to the bloodstream through the renal parenchyma's rich blood supply
• Loin/flank pain: Renal capsular distension from oedema and inflammation (pyelonephritis), or obstruction

• Uncommon for typical UTI organisms
• S. aureus is the classic organism that seeds the kidney via the bloodstream (e.g., from endocarditis or infected IV lines)
• Genitourinary TB: Mycobacterium tuberculosis spreads haematogenously from a primary pulmonary focus to the highly vascular renal cortex → caseous granulomas → "autonephrectomy" in severe cases

Uncomplicated UTI ^[1][2]:

• In anatomically, physiologically normal urinary tract with normal host defence mechanisms (i.e. otherwise normal individuals)
• Usual uropathogens such as E. coli (70–95%)
• Outpatient treatment
• Shorter duration of treatment
• No increased risk of failing standard therapy

Complicated UTI ^[1][2]:

• E.g. neuropathic bladder, urinary tract obstruction, bladder diverticulum, presence of stones
• ↑Risk of acquiring infection and failing treatment
• Broader spectrum of pathogens, often drug-resistant
• Admission may be required
• Longer duration of treatment
• Measures should be made to eradicate the complicating feature

Special groups: pregnancy, children ^[1]

Recurrent UTI is further subdivided:

Classification by clinical syndromes ^[4]:

1. Asymptomatic bacteriuria
2. Acute bacterial infections:
   • Upper tract: pyelonephritis, pyonephrosis, renal abscess
   • Lower tract: cystitis, prostatitis, epididymo-orchitis, urethritis and STDs
3. Other infections: mycobacterial, parasitic, fungal infections

The table from the lecture slides summarises the categories:

^[1]

Risk factors of UTI in children ^[1]:

• Age: neonates and infants have increased bacterial colonisation of the periurethral area and an immature immune system, especially first few weeks
• Vesicoureteric reflux
• Genitourinary abnormalities (pelviureteric or vesicoureteric obstruction; ureterocele; posterior urethral valves)
• Voiding dysfunction (abnormal bladder activity, compliance, or emptying)
• Foreskin: uncircumcised boys have a 10-fold higher risk of UTI in the first year due to bacterial colonisation of the glans and foreskin
• Constipation

Why is VUR important?

• VUR allows infected urine to travel retrogradely from the bladder to the kidney → reflux nephropathy → renal scarring → CKD and hypertension
• VUR is found in 30–50% of children presenting with UTI
• Most cases are primary (congenital short intramural ureter → incompetent flap valve mechanism at the ureterovesical junction)
• VUR is graded I–V (International Reflux Study):
  • I–II: into ureter only or non-dilated collecting system
  • III: moderate ureteral/pelvic dilation
  • IV–V: gross dilation with tortuous ureters and loss of papillary impression

• Most common cause of congenital bladder outlet obstruction in males
• Obstructing membrane in the posterior urethra → bilateral hydroureteronephrosis → renal dysplasia if severe
• Presents: antenatal hydronephrosis, poor urinary stream, UTI, failure to thrive, renal failure
• Diagnosis: MCUG (micturating cystourethrogram)
• Management: valve ablation (endoscopic) ± temporary vesicostomy if severe

Bladder and bowel dysfunction is characterised by: ^[2]

• Abnormal elimination pattern (frequent or infrequent voids, daytime wetting, urgency, infrequent stool)
• Bladder or bowel incontinence
• Withholding manoeuvre

Why does this matter for UTI?

• Incomplete bladder emptying → residual urine → bacterial proliferation
• Constipation → rectal distension compresses bladder → ↓bladder capacity and ↑residual volume
• BBD perpetuates UTI and VUR → must treat both to break the cycle

Dysuria = "dys" (difficult/painful) + "uria" (urination). It is the most common symptom that brings a patient to consider UTI. But dysuria has a differential that varies by sex ^[3][4]:

Clinical pointers to distinguish these ^[3][4]:

When a patient presents with classic lower UTI symptoms, the differential is narrower ^[4]:

D/dx of acute cystitis ^[4]:

• Vaginitis (e.g. STDs, BV) → vaginal pruritus, discharge
• Pyelonephritis → systemic upset, flank pain/renal angle tenderness, Murphy's kidney punch positive
• Non-infective lower urinary tract pathologies, e.g. interstitial cystitis, bladder stones

Key principle: If there is fever or flank pain, it is NOT just cystitis — you must consider pyelonephritis (upper tract infection). If there is vaginal discharge, you must consider a gynaecological/STD cause rather than true cystitis.

Haematuria is the most common presentation of UTI (60% of haematuria cases) but the most worrying cause is malignancy (until proven otherwise) ^[6].

When haematuria accompanies UTI symptoms, you must ensure it resolves after treatment. If it persists, the differential broadens significantly ^[3][7]:

Crucial anatomical localisation by timing of haematuria in the stream ^[7]:

• Initial stream → anterior urethra (distal to urogenital diaphragm)
• Terminal stream → bladder neck or posterior urethra
• Throughout → bladder and upper urinary tract

UTI presents with predominantly storage (irritative) symptoms. The full differential of LUTS includes ^[5]:

Why does BOO cause OAB? When the bladder has to contract against a chronically obstructed outlet (e.g. BPH), the detrusor muscle undergoes hypertrophy and develops unstable, involuntary contractions → secondary detrusor overactivity → storage symptoms superimposed on voiding symptoms.

This is an important concept. Pyuria does not equate infection. ^[1] When you find WBCs in the urine but the standard culture is negative, the differential is:

When a patient presents with the classic pyelonephritis triad (fever + loin pain + renal angle tenderness), the differential includes ^[2][4]:

Some abdominal and gynaecological conditions can mimic UTI or present alongside it ^[2]:

When a patient has recurrent UTI (≥ 2 in 6 months or ≥ 3 in 12 months), you must differentiate between ^[1][4][6]:

1. Bacterial reinfection (> 95% of cases): caused by different organisms or same organism but separated by documented periods of no growth in urine; source of organisms likely reservoir in faecal flora; indicates underlying susceptibility (e.g. genetic) to UTI ^[1]

2. Bacterial persistence/relapse: recurrent UTI caused by the same organism, frequently from a focus within the urinary tract (e.g. stones, urethral diverticulum) ^[1]

The approach to recurrent UTI ^[6]:

• Check documented culture: urine C/ST if not available
  • Culture negative: consider stones / TB / tumour
  • Rule out treatment failure: resistant strain / incorrect antibiotics / poor compliance to treatment
• True recurrent UTI: check culture pattern to differentiate reinfection from persistence

When a male presents with dysuria and discharge, the differential is specifically ^[9]:

Key distinguishing features ^[9]:

When gas is seen in the bladder on imaging, the DDx includes ^[1]:

• Instrumentation (recent cystoscopy, catheterisation)
• Fistula to hollow viscus (colovesical fistula from diverticulitis, Crohn's, colorectal cancer)
• Tissue infarct with necrosis
• Infection (emphysematous cystitis)

General approach ^[2]:

• Screening test: sent for microscopy for pyuria or bacteriuria, dipstick for leukocyte esterase, nitrite and ANY positive results should lead to confirmatory tests
  • Choice of urine collection: bag urine
• Confirmatory test: sent for microscopy (pyuria/bacteriuria), leukocyte esterase, nitrite and culture with sensitivity test
  • Choice of urine collection:
    • < 12 months: suprapubic aspiration / clean-catch urine / catheterised urine
    • > 12 months: midstream urine / clean-catch urine / catheterised urine

Workup of suspected UTI should include ^[1]:

• Associated gross haematuria?
• Previous antibiotic treatment
• Presence of "complicated" features
  • E.g. neuropathic bladder, renal stone, previous surgery to urinary tract
• Recurrent attack?
• Social & drug history: ?ketamine use

The specimen collection method critically determines the reliability of results. ↑Invasiveness = ↓contamination risk ^[4].

The urine dipstick is a rapid bedside screening tool. Two key markers are used for UTI:

Dipstick interpretation logic for UTI:

Practical approach: If either LE or nitrite is positive, send urine for culture and treat based on clinical picture. If both are negative, UTI is very unlikely and you should reconsider the diagnosis ^[2].

Microscopy provides direct visualisation of cellular elements and is more informative than dipstick alone.

This is the gold standard for confirming UTI and guiding antibiotic therapy.

When is urine C/ST indicated?

Interpreting culture results:

Imaging is not required in most UTI → to look for underlying factors amenable to non-medical means and diagnosis of focus of bacterial persistence ^[4]

After acute UTI in children, imaging is performed to detect VUR, obstruction, and renal scarring — because these are correctable/monitorable causes that can prevent long-term renal damage.

^[2]

NICE Definitions ^[2]:

• Recurrent UTI: ≥ 2 episodes of upper UTI; 1 episode of upper UTI + ≥ 1 episode of lower UTI; ≥ 3 episodes of lower UTI
• Atypical UTI: seriously ill; poor urine flow; abdominal or bladder mass; elevated serum creatinine; septicaemia; failure to respond to treatment with suitable antibiotics within 48 hours; infection with non-E. coli organisms

• Diagnosis is primarily clinical — classic triad of dysuria + frequency + urgency without systemic symptoms
• Dipstick is usually sufficient for confirmation (LE+ and/or Nitrite+)
• Urine C/ST not mandatory for first episode — can treat empirically ^[4]
• No imaging required

• Clinical diagnosis supported by fever ≥ 38°C + flank pain/CVA tenderness
• Urine C/ST always required ^[4]
• Blood culture should be obtained ^[4]
• Bloods: CBC, RFT, CRP/ESR
• USG kidney: mandatory for severe infection to rule out obstruction ^[4]
• Contrast CT A+P if no improvement > 72 hours → to rule out renal abscess and obstruction ^[4]

• Dx: clinical + urinalysis (WBC > 10/mm³) + culture (routine in males, > 10³ CFU/mL) ^[4]
• Need for further evaluation: 50% have underlying urological abnormalities ^[4]
• Indications for further evaluation (should focus on lower urinary tract): severe UTI (febrile UTI, pyelonephritis), recurrent UTI → to rule out chronic prostatitis, history of voiding difficulties and AROU, persistent microscopic haematuria ^[4]

• Always obtain urine C/ST to document organisms and sensitivities
• Check documented culture: urine C/ST if not available ^[5]
  • Culture negative: consider stones / TB / tumour ^[5]
  • Rule out treatment failure: resistant strain / incorrect antibiotics / poor compliance to treatment ^[5]
• Imaging (USG ± CT) if evidence of bacterial persistence, recurrent Proteus spp, history of stones, persistent haematuria ^[4]
• Cystoscopy if persistent haematuria or suspected lower tract pathology

Asymptomatic bacteriuria refers to ≥ 10³ CFU/mL in males and ≥ 10⁵ CFU/mL in females and requires screening and treatment ONLY in pregnancy or patients undergoing genitourinary procedure with risk of mucosal bleeding and sepsis ^[2].

Routine screening and treatment of asymptomatic bacteriuria in pregnant patients is due to higher risk of progression into UTI and its association with prematurity and low birth weight ^[2].

This is the bread-and-butter scenario: a young, otherwise healthy woman with dysuria, frequency, and urgency, no fever, no flank pain.

Treatment can be given empirically without urine C/ST for uncomplicated cases ^[4]

General measures:

• ↑Fluid intake ^[4] — why? Increased urine output "washes out" bacteria and dilutes bacterial concentration. Aim 2–3 L/day
• Pyridium (phenazopyridine) to ↓discomfort ^[4] — this is a urinary analgesic that acts directly on the bladder mucosa to reduce pain, burning, and urgency. It turns urine bright orange (warn the patient!)

Antibiotic regimen — current Hong Kong guidance / IMPACT 6th edition ^[4][8][9]:

Avoid empirical fluoroquinolones for uncomplicated cystitis unless other commonly prescribed options are inappropriate — local E. coli levofloxacin resistance is 36–46%, and fluoroquinolones have potentially disabling or long-lasting adverse effects ^[8]. Co-trimoxazole is not recommended first-line because local E. coli resistance is 31–32% ^[8].

Understanding each antibiotic from first principles:

Complicated cystitis: refer to cystitis in functionally/structurally abnormal urinary tracts ^[4]

Complicating features: pregnancy, DM, immunocompromised states, recent Abx use, recent urinary tract intervention, nosocomial infection ^[4]

Treatment differs in three important ways:

1. Generally require longer duration treatment, e.g. 10–14d culture-guided therapy; use fluoroquinolones only if susceptibility and patient factors support it ^[4]
2. Measures should be made to eradicate the complicating feature ^[4]
3. Urine C/ST is mandatory — broader pathogen spectrum, higher resistance rates

Management ^[4]:

• Hospitalisation if severe or suspicious of obstruction
• Prompt empirical Abx:
  • Choice: IV Augmentin → Tazocin if suspect P. aeruginosa → Imipenem or Meropenem if severe or rapidly deteriorating
  • Regimen: IV until afebrile 24–48h → complete 14-day course with oral drugs
• Contrast CT A+P if no improvement > 72h → to rule out renal abscess and obstruction

Step-by-step approach:

Antibiotic escalation ladder for pyelonephritis:

Mild (outpatient, selected stable patients):
  PO Augmentin or another culture-appropriate oral agent
  Avoid empirical fluoroquinolone unless other options are unsuitable
  and susceptibility/local resistance supports use
        ↓ (if worsening or not tolerating PO)
Moderate (inpatient):
  IV Augmentin (amoxicillin-clavulanate 1.2g TDS)
        ↓ (if P. aeruginosa suspected — catheter, instrumentation, nosocomial)
  IV Tazocin (piperacillin-tazobactam 4.5g TDS)
        ↓ (if severe / rapidly deteriorating / ESBL suspected)
  IV Meropenem (1g TDS) or Imipenem (500mg QDS)

Why these specific escalation choices?

• Augmentin: Good first-line IV; covers most community E. coli and Enterobacteriaceae; β-lactamase inhibitor extends spectrum
• Tazocin ("tazo" = tazobactam, a β-lactamase inhibitor; "cin" from piperacillin): Broader Gram-negative coverage including Pseudomonas aeruginosa; the go-to when Pseudomonas is suspected
• Meropenem/Imipenem: Carbapenems — the "big guns." Stable against ESBL enzymes. Reserved for severe/resistant cases because overuse drives carbapenem-resistant Enterobacteriaceae (CRE), which is a public health catastrophe

EPN management ^[1]:

• High index of suspicion in patient failing medical treatment for acute pyelonephritis
• Active resuscitation — ABC
• Medical management (MM):
  • O₂, IVF, acid-base balance, Abx, good glycaemic control
  • Keep SBP > 100 with IVF ± inotropes
  • Empirical Abx: aminoglycoside, β-lactamase inhibitor, cephalosporin, quinolones — until C/ST available
  • Renal support if ARF
  • ICU care if multiorgan support needed

Surgical / interventional management:

• Percutaneous drainage (PCD): CT-guided or USG-guided insertion of drain into gas-containing collection. First-line intervention in most EPN
• Nephrectomy: Reserved for patients failing PCD + medical management, or those with non-functioning kidney (destroyed by gas-forming infection)
• The traditional approach of immediate nephrectomy has shifted to a stepwise approach: medical → PCD → nephrectomy only if failing ^[1]

Male UTI: very uncommon, incidence only 5–8/10k/year ^[4]

Mx: generally need longer (7d) treatment for male cystitis ^[4]

Why longer? Males have a longer urethra and the prostate can harbour bacteria — a 3-day course may sterilise the urine but leave bacteria in the prostate → relapse. Seven days provides a better chance of eradicating the prostatic reservoir.

Mx: Empirical Abx — prefer quinolone (excellent prostatic penetration) for 2–6 weeks ^[4]

Why quinolones specifically for prostatitis?

• The prostate has a blood-prostate barrier (similar in concept to the blood-brain barrier) composed of prostatic epithelial cells with tight junctions
• Most antibiotics penetrate poorly into prostatic tissue
• Fluoroquinolones are small, lipophilic molecules with excellent penetration across this barrier (achieving prostatic concentrations 2–3× serum levels)
• Co-trimoxazole also penetrates well and is an alternative
• β-lactams and aminoglycosides penetrate poorly → NOT suitable for prostatitis

This was covered in the diagnostic section but the management implications are critical:

Recurrent cystitis: 20% of females with UTI will recur within 6 months → common, genetically determined ^[4]

Management follows a stepwise approach:

Step 1: Behavioural changes ^[4]

Step 2: Topical oestrogen for postmenopausal women

• Topical oestrogen for postmenopausal women: ↓75% incidence of cystitis in RCTs ^[4]
• Mechanism: Restores vaginal glycogen → ↑Lactobacilli → ↓vaginal pH → ↓periurethral colonisation by uropathogens
• Applied intravaginally (cream or pessary), NOT systemic HRT
• This is one of the most effective interventions for recurrent UTI in postmenopausal women

Step 3: Antimicrobial prophylaxis ^[4]

Indication: recurrent symptoms that are specific for UTI persists despite non-Rx measures ^[4]

Don't give Abx for non-specific symptoms, e.g. mental status changes without genitourinary symptoms in elderly ^[4]

Step 4: Investigate and correct bacterial persistence (if suspected)

When the same organism keeps recurring, consider:

• Source of bacterial persistence: infected urinary stones, infected atrophic kidneys, ureteral stump after nephrectomy, medullary sponge kidney, papillary necrosis, infected urachal cyst, urethral diverticulum and urinary fistula ^[2]
• Imaging (USG ± CT) to identify the focus
• Surgical correction of the focus

Antibiotic prophylaxis should NOT be routinely prescribed to young children with first episode of UTI ^[2]

Acute treatment:

Aminoglycosides (e.g. gentamicin, amikacin): should not be used as monotherapy (with 3rd generation cephalosporin). NOT effective in treating Enterococcus infection ^[2] Enterococcus is intrinsically resistant to cephalosporins and aminoglycosides and therefore should use Augmentin or nitrofurantoin ^[2]

Prophylaxis in children ^[2]:

Surgical intervention for VUR ^[1][2]:

Surgical intervention for: breakthrough infections, poor compliance with meds, renal scarring ^[1]

Indications for surgical referral ^[2]:

• Recurrence of UTI (2nd episode) + VUR > Grade 3 + significant scarring on DMSA
• Recurrence of UTI (3rd episode) despite antibiotic prophylaxis + VUR > Grade 3
• NOT suggested for patients with Grade 1 and 2 VUR since there is a high likelihood of spontaneous resolution and low risk of renal scarring

The most fundamental "complication" of lower UTI is its ascent into the upper tract. Uncomplicated cystitis in a healthy woman rarely progresses, but in the presence of complicating factors (VUR, obstruction, catheter, DM, immunosuppression), bacteria can ascend the ureters and invade the renal parenchyma.

Why does this matter? Because the kidney, unlike the bladder, has a rich blood supply that communicates directly with the systemic circulation. Once bacteria reach the renal parenchyma, they have a portal into the bloodstream → potential for bacteraemia and sepsis. The bladder mucosa, by contrast, is relatively avascular and acts as a barrier to systemic spread — which is why uncomplicated cystitis almost never causes fever or bacteraemia.

± Complications: especially if obstruction, recent instrumentation, prior urinary tract abnormalities, DM, immunocompromised ^[4]

Spread of infection: renal corticomedullary abscess, perinephric abscess ^[4]

Risk factors: DM, pregnancy, anatomical abnormalities (renal stones, PCKD, renal cyst, obstructive tumour), functional abnormalities (neurogenic bladder, VUR) ^[4]

Microbiology: E. coli (51.4%), S. aureus (10.0%), K. pneumoniae (8.6%) ^[4]

Why does DM keep appearing as a risk factor? Diabetes creates a "perfect storm" for complicated UTI:

1. Glycosuria = substrate for bacterial growth
2. Diabetic cystopathy = neurogenic bladder → incomplete emptying → stasis
3. Impaired neutrophil chemotaxis and phagocytosis → ↓bacterial clearance
4. Microangiopathy → impaired tissue perfusion → ↓antibiotic delivery to infected tissue

"Pyo" (Greek: πύον) = pus + "nephrosis" = kidney condition. This is pus under pressure in an obstructed collecting system — a urological emergency.

This is a life-threatening necrotising infection characterised by gas formation within the renal parenchyma and surrounding tissues. Covered in detail in the management section. Key complication points:

• Mortality historically 50–80% if treated medically alone; with modern approach (PCD + antibiotics ± nephrectomy), mortality ~20%
• EPN associated factors: DM — single most common factor; Female > Male; urinary tract obstruction; stones; immunocompromised ^[1]

Gas formation in the bladder wall. Less immediately dangerous than EPN but can progress:

Various S/S: asymptomatic, pneumaturia, irritative voiding, acute abdomen to severe sepsis ^[1]

A rare, chronic destructive granulomatous process of the kidney, almost always unilateral:

Urosepsis: systemic sepsis, shock, multi-organ failure ^[4]

Urosepsis is the most feared systemic complication of UTI. It occurs when bacteria and their products (especially Gram-negative LPS endotoxin) enter the bloodstream from an infected urinary tract → triggering the systemic inflammatory response syndrome (SIRS) → sepsis → septic shock → multi-organ dysfunction.

Risk factors for urosepsis:

• Obstruction (the single most important factor — pus under pressure)
• Recent urological instrumentation
• DM and immunosuppression
• Complicated UTI: ↑risk of progression into sepsis/death ^[4]
• Elderly and frail patients

Management: Sepsis bundles (SSC guidelines) — early recognition, blood cultures, empirical broad-spectrum antibiotics within 1 hour, aggressive fluid resuscitation, vasopressors if needed, source control (drainage of obstructed/infected system).

Acute renal failure ^[4] can complicate UTI through multiple mechanisms:

Prolonged pre-renal and post-renal disease will progress to become ATN and tubulointerstitial fibrosis respectively, i.e. intrinsic renal disease ^[6]

This is why early recognition and treatment matter — reversible pre-renal and post-renal AKI become irreversible intrinsic renal damage if left too long.

± Complications: bacteraemia and sepsis, endocarditis, epididymitis, chronic prostatitis, prostatic abscess ^[4]

UTI (and especially untreated asymptomatic bacteriuria) in pregnancy carries specific risks:

This is precisely why asymptomatic bacteriuria is screened for and treated in pregnancy — it's the only reliable way to prevent these complications.

This is the most important long-term complication in paediatric UTI:

Urinary tract TB: often diagnosed late with complications such as urethral or ureteric strictures, renal failure, infertility ^[1]

Recurrent UTI with urease-producing organisms (Proteus, Klebsiella, Pseudomonas, Staphylococcus) creates a vicious cycle:

Urease-producing bacteria colonise urinary tract
            ↓
Urease breaks down urea → ammonia + CO₂
            ↓
Ammonia alkalinises urine (pH > 7.5)
            ↓
Supersaturation with magnesium ammonium phosphate
            ↓
STRUVITE STONE formation (can grow rapidly into staghorn calculi)
            ↓
Stone acts as nidus for bacterial persistence → recurrent UTI
            ↓
Cycle perpetuates

Struvite crystal due to urease-positive bacterial infection ^[3]. This is why repeated Proteus spp isolation should prompt imaging to look for stones ^[4].

Repeated episodes of pyelonephritis (particularly with VUR or obstruction) → progressive tubulointerstitial fibrosis → cortical thinning and scarring → CKD → eventually end-stage renal disease in severe cases.

Chronic UTI and chronic indwelling catheter use (years) → chronic irritation → squamous metaplasia of the urothelium → squamous cell carcinoma (not the usual transitional cell carcinoma). This is:

• Seen in patients with long-term indwelling catheters (> 10 years)
• Associated with chronic UTI as a risk factor ^[8]
• Also associated with schistosomiasis (S. haematobium — not common in HK but important for travel history)