Infeksi Saluran Kemih

01Pathophysiology

The vast majority of urinary tract infections develop via an ascending route of infection. Uropathogenic bacteria, most commonly E. coli, originate from the lower gastrointestinal tract and colonize the periurethral and distal urethral mucosa. From there, the organisms ascend through the urethra into the bladder, and in some cases continue upward into the ureters and renal parenchyma. This is why UTI is predominantly a disease of women: the female urethra is significantly shorter than the male urethra, and the urethral meatus sits in close anatomical proximity to the anus, which serves as the reservoir for enterogenic uropathogens (PNPK ISK 2025).

Uropathogenic E. coli (UPEC) carries critical virulence factors, most notably fimbriae (type 1 and P fimbriae), which allow the bacteria to adhere to uroepithelial cells, resist the flushing mechanism of voiding, and stimulate proinflammatory mediator release. This adherence-invasion-inflammation cascade is what produces the clinical symptoms of dysuria, frequency, and urgency. When bacteria ascend to the kidney, the intense inflammatory response in the renal parenchyma leads to tissue damage and, particularly in children, the formation of renal scarring (PNPK ISK 2025).

Several host defense mechanisms normally protect against UTI: intact mucosal barriers, the glycosaminoglycan layer coating the bladder epithelium, normal urinary flow that mechanically washes out bacteria, the acidic pH of urine, and both innate and adaptive immune responses. The vaginal flora in premenopausal women, maintained by estrogen, also inhibits colonization by uropathogens. When any of these defenses are compromised, the balance tips in favor of infection.

In complicated UTI, the pathogenic mechanism is augmented by factors that impair the host's ability to clear bacteria. Urinary obstruction (from stones, prostatic hypertrophy, or congenital anomalies) causes urinary stasis, allowing bacteria to multiply unimpeded. Indwelling catheters damage the glycosaminoglycan layer and provide a surface for biofilm formation, which shields organisms from both antibiotics and the immune system. In children with congenital anomalies of the kidney and urinary tract (CAKUT), vesicoureteral reflux allows infected urine to flow retrograde into the ureters and renal pelvis, markedly increasing the risk of pyelonephritis and subsequent scarring (PNPK ISK 2025).

Hematogenous spread to the urinary tract is uncommon in immunocompetent individuals but can occur with organisms like S. aureus, Candida spp, Salmonella spp, and Mycobacterium tuberculosis. In neonates, whose immune systems are immature, hematogenous seeding of the kidney is proportionally more common than in older children and adults (PNPK ISK 2025).

02Classification and Clinical Manifestation

Classification (PNPK ISK 2025)

Clinical Manifestations

Pediatric UTI Classification (PNPK ISK 2025)

03Diagnostic Workup

The best initial test for a patient presenting with lower urinary tract symptoms (dysuria, frequency, urgency) in the outpatient setting is the urine dipstick. A positive leukocyte esterase indicates pyuria, while a positive nitrite indicates the presence of nitrate-reducing bacteria, predominantly Enterobacterales such as E. coli. The dipstick is particularly useful for ruling in uncomplicated cystitis. Importantly, nitrite can be negative if the urine has not been in the bladder for at least 4-6 hours (the time bacteria need to convert nitrate to nitrite), if the causative organism does not produce nitrate reductase (e.g., Enterococcus, S. saprophyticus), or if the patient has very dilute urine. Therefore, a negative nitrite does NOT rule out UTI (PNPK ISK 2025).

The gold standard and most accurate test is the urine culture with antimicrobial susceptibility testing. However, not every case of UTI requires culture. According to the PNPK ISK 2025, uncomplicated cystitis in women with classic symptoms and a positive dipstick can be treated empirically without culture. Culture is indicated when:

1. Pyelonephritis is suspected

2. Symptoms persist or recur within 4 weeks after completing therapy

3. Atypical symptoms are present

4. The patient is pregnant

5. The patient is male

6. Complicated UTI or catheter-associated UTI is suspected

Quantitative culture thresholds vary by specimen collection method and clinical scenario (PNPK ISK 2025):

For imaging, renal ultrasound is the first-line modality for evaluating the upper urinary tract, recommended within 24 hours for pyelonephritis to detect obstruction requiring urgent drainage. CT scan is reserved for cases where the patient fails to improve after 48-72 hours of appropriate antibiotics, or when serious complications (abscess, emphysematous pyelonephritis) are suspected. In pregnant patients, ultrasound or MRI is preferred to avoid ionizing radiation (PNPK ISK 2025).

In children, the PNPK ISK 2025 recommends renal and bladder ultrasound for all febrile UTI episodes in infants <24 months and all cases of suspected upper tract UTI. VCUG is considered for all children <2 years with febrile first-episode UTI (particularly with severe initial infection) and for recurrent febrile UTI. DMSA scan is considered for children <2 years with febrile UTI and for older children with clinical evidence of pyelonephritis.

04Management and Treatment

Acute Uncomplicated Cystitis is the most common presentation and the simplest to manage. According to the PNPK ISK 2025, first-line agents are fosfomycin trometamol, pivmecillinam, or nitrofurantoin. These agents are preferred because they achieve high urinary concentrations, have favorable resistance profiles, and produce minimal collateral ecological damage. TMP-SMX and fluoroquinolones are alternative agents but should be used only when local resistance to TMP-SMX is <20%. Empiric treatment can begin after a positive dipstick in women with typical symptoms without requiring urine culture. If symptoms resolve after treatment, post-treatment culture is unnecessary.

A longer 7-day course is reserved for patients with factors predicting lower treatment success: symptoms lasting >7 days, age >65 years, or diaphragm use (PNPK ISK 2025).

Pyelonephritis requires a more aggressive approach. Outpatient management with oral fluoroquinolones or, if sensitivity is confirmed, TMP-SMX is appropriate for hemodynamically stable patients who can tolerate oral medications. Indications for hospitalization include inability to maintain hydration or tolerate oral antibiotics, severe illness or debilitation, failure of outpatient oral therapy, need for further investigation, pregnancy, and comorbidities such as diabetes or advanced age. Once hospitalized, patients receive IV antibiotics for a minimum of 48 hours, then step down to oral therapy once clinically improved and able to tolerate oral intake. If fever persists beyond 48-72 hours, re-evaluate for complications such as obstruction or abscess and consider repeat imaging with CT scan (PNPK ISK 2025).

Key Contraindications:

• Nitrofurantoin: contraindicated when eGFR <30 mL/min/1.73 m^2 (drug accumulation with increased adverse effects and treatment failure). Also avoid late in pregnancy and in G6PD deficiency.

• TMP-SMX: avoid in first trimester (teratogenic potential of trimethoprim) and third trimester (sulfonamide component).

• Fluoroquinolones in children: restricted to infections caused by Pseudomonas aeruginosa or multidrug-resistant Gram-negative organisms to prevent resistance.

• Fosfomycin and nitrofurantoin in pyelonephritis: must be avoided because they do not achieve adequate renal tissue concentrations (PNPK ISK 2025).

• Ceftriaxone in neonates: may affect bilirubin transport in the liver.

Urosepsis is a medical emergency. The PNPK ISK 2025 mandates broad-spectrum parenteral antibiotics within one hour of clinical suspicion, empirically targeting both Gram-positive and Gram-negative organisms, including resistant strains. Source control is equally critical: drainage of obstruction, removal of foreign bodies (stones, catheters), and abscess drainage are emergent interventions. Supportive care includes fluid resuscitation with crystalloids (or albumin if crystalloids are insufficient), norepinephrine as the first-line vasopressor (target MAP approximately 65 mmHg), hydrocortisone if vasopressors fail, and monitoring of serum lactate and procalcitonin.

Recurrent UTI prophylaxis options include post-coital single-dose prophylaxis (TMP-SMX 40-200 mg, nitrofurantoin 50-100 mg, or cephalexin 250 mg) for sexually-associated recurrences, or continuous low-dose prophylaxis at bedtime for 3-6 months when there are more than 3 episodes per year (PNPK ISK 2025).

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common trap on this topic is treating asymptomatic bacteriuria when you should not. Test-writers love to give you an elderly patient in a nursing home, a patient with a well-controlled diabetes, or a patient with a chronic indwelling catheter who has a positive urine culture but no symptoms, and then ask for the next best step. The answer is almost always "no treatment." According to the PNPK ISK 2025, screening for and treating asymptomatic bacteriuria is strongly recommended only in pregnant women and before endoscopic urological procedures that breach mucosa. All other groups (postmenopausal women, controlled diabetics, elderly institutionalized patients, spinal cord injury patients, renal transplant recipients, patients before arthroplasty) should NOT be screened or treated.

A second major pitfall is confusing the quantitative thresholds for culture positivity. A vignette describing a woman with acute dysuria and a midstream urine culture growing 10^3 CFU/mL of E. coli is diagnostic of uncomplicated cystitis, but students who memorize only the "10^5" threshold will incorrectly call this a contaminated specimen. The 10^5 threshold applies to asymptomatic bacteriuria. In symptomatic acute cystitis, 10^3 is the diagnostic cutoff, and in suprapubic aspiration, any growth at all is considered significant (PNPK ISK 2025).

Third, remember that nitrofurantoin and fosfomycin are only appropriate for lower tract infection (cystitis). These agents do not achieve adequate renal tissue levels and must never be used for pyelonephritis. A vignette describing flank pain, fever, and costovertebral angle tenderness in a patient being prescribed nitrofurantoin is testing whether you recognize this as an inappropriate drug choice for upper tract disease.

Fourth, in pediatrics, always think about underlying structural abnormalities (CAKUT, VUR) in any child presenting with a febrile UTI, especially in infants. The PNPK ISK 2025 mandates renal ultrasound for all febrile UTI in children <24 months and VCUG consideration in children <2 years old, particularly in severe presentations. Missing congenital anomalies leads to recurrent infection and renal scarring.

Finally, in urosepsis, the core competency being tested is timing and sequencing. Antibiotics must be given within one hour of clinical suspicion, cultures (urine and two sets of blood cultures) must be drawn before starting antibiotics, and source control (drainage of obstruction, removal of catheter or foreign body) must happen emergently. A vignette presenting obstructive pyelonephritis with sepsis is testing whether you know that antibiotics alone are insufficient: the obstructed system must be decompressed.