Infectious DiseasesTier 1Approach to a presentation

Dysuria

Red flags

  • Fever, rigors, loin pain, vomiting -> pyelonephritis, not cystitis
  • Sepsis - hypotension, tachycardia, confusion, lactate; urosepsis is the commonest source of Gram-negative sepsis in older adults
  • Anuria or oliguria with pain -> obstructed infected kidney = a urological emergency requiring drainage, not antibiotics alone
  • Known stone, single kidney, transplant kidney, recent instrumentation, indwelling stent or catheter
  • Male sex - no UTI in a man is "uncomplicated"
  • Pregnancy - asymptomatic bacteriuria and cystitis both require treatment
  • Visible haematuria persisting after treatment, or non-visible haematuria with irritative symptoms in a smoker >50 -> urothelial malignancy
  • Immunosuppression, neutropenia, poorly controlled diabetes
  • Genital ulceration, urethral discharge, or a new sexual partner -> STI, not UTI
  • Scrotal/testicular pain -> torsion or epididymo-orchitis
  • Failure to respond to 48-72 h of appropriate therapy -> abscess, obstruction, resistance, or wrong diagnosis

Differential by mechanism

By mechanism

1. Infective - urinary tract

  • Uncomplicated cystitis - E. coli ~75-85%, Klebsiella, Proteus, Staphylococcus saprophyticus (young women), Enterococcus
  • Complicated UTI - structural/functional abnormality, male, pregnancy, catheter, immunosuppression, resistant organism
  • Acute pyelonephritis
  • Prostatitis - acute bacterial (septic, exquisitely tender prostate) or chronic
  • Renal or perinephric abscess, emphysematous pyelonephritis (diabetes)

2. Infective - sexually transmitted

  • Chlamydia, gonorrhoea, Mycoplasma genitalium -> urethritis
  • HSV - dysuria with vulval/penile ulceration; can cause urinary retention
  • Trichomonas - frothy discharge, strawberry cervix
  • Candida vulvovaginitis - external, "burning as urine passes over the skin", not internal dysuria

3. Non-infective inflammatory

  • Atrophic vaginitis / genitourinary syndrome of menopause - a very common and treatable cause in older women
  • Interstitial cystitis / bladder pain syndrome - pain filling, relief on voiding, sterile urine, no response to antibiotics
  • Radiation or chemical cystitis; cyclophosphamide (haemorrhagic cystitis)
  • Lichen sclerosus, lichen planus, contact dermatitis (soaps, spermicides)
  • Ketamine uropathy - young, recurrent severe symptoms, contracted bladder

4. Structural / obstructive

  • Urolithiasis (distal ureteric stone gives dysuria and frequency), BPH, urethral stricture, foreign body

5. Neoplastic

  • Bladder carcinoma, carcinoma in situ (CIS presents with irritative symptoms and sterile pyuria - the classic trap), prostate, vulval or urethral cancer

6. Other

  • Sterile pyuria -> think: prior antibiotics, STI, TB, stones, malignancy, interstitial nephritis, appendicitis/adjacent inflammation
  • Drugs - ketamine, cyclophosphamide, NSAIDs (AIN)

Focused history

  • Which symptoms?
    • Internal dysuria + frequency + urgency + suprapubic pain, no vaginal discharge or irritation -> probability of UTI >90%
    • External dysuria (burning on the skin) -> vulvovaginitis, HSV, dermatitis
  • Systemic features - fever, rigors, loin pain, vomiting -> upper tract
  • Haematuria - visible, timing in the stream, persistence after treatment
  • Vaginal discharge, itch, ulceration, dyspareunia - the presence of discharge markedly lowers the probability of UTI
  • Sexual history - ask everyone: new or multiple partners, condom use, sites of exposure, partner symptoms
  • Recurrence pattern: how many episodes in 6/12 months, relation to intercourse, cultures and antibiotics used, prior resistant organisms
  • Complicating factors: pregnancy, diabetes, stones, catheter, recent instrumentation, immunosuppression, renal transplant, neurogenic bladder
  • Voiding: stream, hesitancy, incomplete emptying, retention, constipation
  • Menopausal status and vaginal oestrogen use
  • Drugs - recent antibiotics, ketamine, cyclophosphamide
  • Travel and TB risk

Focused examination

  • Vital signs - fever, tachycardia, hypotension (sepsis)
  • Abdomen - suprapubic tenderness, palpable bladder (retention), loin/renal angle tenderness
  • Genital examination - do it
    • Women: vulval inspection for ulcers, atrophy, lichen sclerosus, discharge; speculum and bimanual if discharge, PID or cervical motion tenderness is suspected
    • Men: urethral meatus and discharge, foreskin, epididymis and testis, rectal examination for prostate (gentle - vigorous massage in acute prostatitis risks bacteraemia)
  • Skin - rash, lesions elsewhere (HSV, Behçet, reactive arthritis)
  • Joints and eyes if reactive arthritis is possible
  • In the frail older patient, look for the alternative source before attributing delirium to the urine

Investigation strategy

Uncomplicated cystitis in a non-pregnant woman
  • *No investigation is required* - typical symptoms alone justify empirical treatment
  • Dipstick adds little where the probability is already high
Urine dipstick - understand what it does
  • Nitrites: specific, insensitive (only nitrate-reducing Enterobacterales; needs bladder dwell time; negative in Enterococcus, Staph. saprophyticus, Pseudomonas)
  • Leucocyte esterase: sensitive, non-specific
  • Both negative in a low-probability patient makes UTI unlikely; both positive in an asymptomatic older person means nothing
Urine culture - send it when the result will change management
  • Pregnancy, men, children
  • Pyelonephritis or systemic illness
  • Recurrent or relapsing infection, failed therapy, recent antibiotics
  • Catheter-associated (collect from the port after changing the catheter, never from the bag)
  • Suspected resistance, recent hospitalisation, travel, immunosuppression
  • Collect before antibiotics; midstream, clean-catch
Interpreting the culture
  • >=10^8 CFU/L (10^5 CFU/mL) of a single uropathogen is the classic threshold
    • *Lower counts (10^5-10^7 CFU/L) with typical symptoms still represent infection* - do not dismiss a "low count" in a symptomatic woman
  • Mixed growth usually means contamination - repeat
  • *Asymptomatic bacteriuria is not a UTI - treat only in pregnancy and before urological procedures that breach the mucosa*
STI testing - where the history suggests it
  • First-void urine (or self-collected vaginal swab) NAAT for chlamydia and gonorrhoea; add M. genitalium in persistent urethritis
  • HSV PCR from any ulcer; syphilis and HIV serology
  • Wet mount / NAAT for trichomonas
Bloods and imaging
  • Pyelonephritis/sepsis: FBE, UEC, CRP, lactate, blood cultures
  • Imaging (CT-KUB or renal ultrasound) if:
    • Failure to improve at 48-72 h, suspected obstruction or stone
    • Male, recurrent pyelonephritis, known urological abnormality, diabetes, single/transplant kidney
  • PSA is unreliable during acute prostatitis - defer
Persistent unexplained symptoms with sterile pyuria
  • Early morning urine x3 for mycobacterial culture/PCR
  • Cystoscopy and upper tract imaging - bladder CIS, stones, interstitial cystitis

Management1 exam ›

A. Uncomplicated cystitis, non-pregnant woman
  • *The first-line agent changed in the 2025-2026 Therapeutic Guidelines revision - trimethoprim is no longer first-line because of E. coli resistance in Australian community isolates*
LineRegimen
FirstNitrofurantoin 100 mg orally, 6-hourly for 5 days
SecondFosfomycin 3 g orally, single dose
ThirdTrimethoprim 300 mg orally, daily for 3 days
  • Avoid fluoroquinolones for uncomplicated cystitis - reserve for resistant or complicated infection; tendinopathy, aortic aneurysm, neuropathy, C. difficile
  • Analgesia, hydration; alkalinising agents have no evidence and reduce nitrofurantoin efficacy
  • Nitrofurantoin caution: avoid if eGFR <45 mL/min (inadequate urinary levels, systemic toxicity), at term in pregnancy, and in G6PD deficiency
B. Pregnancy
  • Screen for and treat asymptomatic bacteriuria - untreated -> 20-30% progress to pyelonephritis, preterm birth, low birth weight
  • Nitrofurantoin (avoid at term) or cefalexin; avoid trimethoprim in the first trimester (folate antagonist)
  • Culture-guided, and send a test of cure
C. Male UTI
  • Treat as complicated; consider prostatic involvement
  • Trimethoprim or trimethoprim-sulfamethoxazole, or a fluoroquinolone - agents with prostatic penetration
  • Duration: 7-14 days for cystitis; 2-4 weeks for acute bacterial prostatitis; 4-6 weeks for chronic
  • Beta-lactams penetrate the prostate poorly
D. Acute pyelonephritis
  • Mild, able to take oral therapy, no sepsis: oral therapy for 7-10 days, culture-guided (higher beta-lactam doses are now specified - amoxicillin-clavulanate 875+125 mg 8-hourly, cefalexin 8-hourly)
  • Severe or septic: admit, IV therapy - gentamicin plus amoxicillin (or ampicillin), or ceftriaxone; blood and urine cultures first
  • Step down to oral once afebrile and improving; total 10-14 days
  • Image urgently if not improving at 48-72 h - drain an obstructed infected system (nephrostomy or stent); antibiotics alone will not work
E. Catheter-associated
  • *Do not treat asymptomatic bacteriuria or a positive dipstick in a catheterised patient*
  • Treat only with systemic features; change or remove the catheter before or at the start of treatment
  • Review the indication for the catheter at every opportunity
F. Recurrent UTI in women (>=2 in 6 months or >=3 in 12)

1. Confirm the diagnosis with cultures during symptomatic episodes - many "recurrent UTI" is not UTI

2. Behavioural: fluid intake +1.5 L/day (RCT evidence), post-coital voiding, avoid spermicides, treat constipation

3. Topical vaginal oestrogen in postmenopausal women - the single most effective non-antibiotic intervention

4. Methenamine hippurate - non-antibiotic prophylaxis; non-inferior to antibiotic prophylaxis in the ALTAR trial

5. Post-coital single-dose or continuous low-dose antibiotic prophylaxis - reserve for failure of the above; review at 6 months

6. Patient-initiated self-start therapy with a standby prescription in selected reliable patients

7. Investigate (imaging, cystoscopy) if haematuria, stones, obstruction, male, or persistent single-organism relapse

G. Non-infective causes
  • Atrophic vaginitis -> topical oestrogen
  • Candida -> topical or oral azole
  • Interstitial cystitis/bladder pain syndrome -> stop antibiotics, urology referral, bladder retraining, amitriptyline, intravesical therapy
  • STI -> treat per the Australian STI guidelines, partner notification, notify, retest at 3 months

Traps

  • *Treating asymptomatic bacteriuria. Prevalence reaches 20-50% in aged-care residents and ~100% in long-term catheters. Treatment causes harm and prevents nothing - except in pregnancy and pre-instrumentation*
  • *Diagnosing "UTI" as the cause of delirium in an older person on a dipstick alone.* Look for the real cause; a positive dipstick in a delirious 85-year-old is usually a coincidence
  • *Still reaching for trimethoprim first.* Resistance has moved it to third-line in the current Australian guidance
  • *Dismissing a "low colony count"* in a woman with classic symptoms
  • *Not taking a sexual history* - dysuria with sterile pyuria in a young adult is chlamydia until proven otherwise
  • *Missing external dysuria* - candida, HSV and atrophic vaginitis all get treated as UTI
  • *Nitrofurantoin in significant renal impairment* (eGFR <45) - it will not work and it may cause pulmonary or hepatic toxicity
  • *Treating a man's UTI for 3 days* - inadequate; consider the prostate
  • *Failing to image the non-responder* - an obstructed infected kidney is a surgical emergency
  • *Attributing persistent haematuria to the infection* - non-visible haematuria that persists after treatment needs urological assessment
  • *Forgetting ketamine uropathy* in a young person with severe refractory irritative symptoms
  • *Sterile pyuria dismissed* - TB, stones and bladder CIS all present this way

Talk track

1. Separate the anatomical compartments first

  • "Dysuria localises to the lower urinary tract, the urethra, or the vulva and vagina, and the three have different causes. Internal dysuria with frequency, urgency and suprapubic pain and no vaginal symptoms gives a probability of cystitis above ninety per cent; external dysuria points to a vulval or vaginal cause."

2. Decide whether it is complicated

  • "I then ask whether anything makes this a complicated infection - male sex, pregnancy, a catheter or stent, stones, a transplant or single kidney, immunosuppression, or recent instrumentation - because that changes the investigation, the duration and the threshold for imaging."

3. Be disciplined about investigation

  • "In an otherwise healthy non-pregnant woman with typical symptoms I treat empirically without a dipstick or a culture. I send a culture where the result will change management: pregnancy, men, children, pyelonephritis, recurrence, treatment failure, or suspected resistance."

4. Be explicit that the first-line agent has changed

  • "The current Therapeutic Guidelines make nitrofurantoin first-line for uncomplicated cystitis, with fosfomycin second and trimethoprim third, because community E. coli resistance to trimethoprim has risen to a level where it is no longer reliable empirically."

5. State the asymptomatic bacteriuria rule unprompted

  • "I would not treat asymptomatic bacteriuria. The only exceptions are pregnancy and before a urological procedure that breaches the mucosa. In an older or catheterised patient a positive urine without symptoms is colonisation, and treating it causes C. difficile, resistance and delirium without preventing anything."

6. Escalate on non-response

  • "If a patient is not improving by forty-eight to seventy-two hours I image, because the two things I must not miss are an obstructed infected system needing drainage and a renal or perinephric abscess."

7. Manage recurrence without reflex antibiotics

  • "For recurrent infection I first confirm it is actually infection with cultures during symptomatic episodes, then use increased fluid intake, topical vaginal oestrogen in postmenopausal women, and methenamine hippurate, before considering antibiotic prophylaxis - and I review any prophylaxis at six months."

8 of 8 sections written · drafted 2026-09-12