G35. Urinary Tract Infections

I. Definition and Classification

Definition

• Urinary tract infection: microbial infection of urinary tract with symptoms and usually pyuria/bacteriuria.
• Asymptomatic bacteriuria: significant bacteriuria without urinary symptoms; important in pregnancy and before selected urologic procedures.

Anatomic Classification

1. Lower UTI: urethritis, cystitis.
2. Upper UTI: pyelonephritis ± renal/perinephric abscess.
3. Catheter-associated UTI: UTI related to urinary catheter or recent catheterization.

Clinical Classification

• Uncomplicated cystitis: lower UTI in immunocompetent, non-pregnant woman without relevant structural/neurologic urinary tract disease.
• Complicated UTI: pregnancy, obstruction/stone/catheter, immunosuppression, significant comorbidity, renal disease, resistant organism or systemic infection.
• Systemic UTI: fever, chills, flank pain, malaise, sepsis signs → think pyelonephritis or complicated infection.

Sterile Pyuria / Differential Diagnosis

• Pyuria without typical bacteriuria: vaginal contamination/discharge, urethritis, stones, tumor, interstitial nephritis, renal tuberculosis, foreign body.
• Dysuria with vaginal discharge/irritation: consider vaginitis, cervicitis or STI rather than simple cystitis.

II. Risk Factors and Pathogenesis

Risk Factors for Complicated Course

• Pregnancy, symptoms > 7 days or recurrent infection.
• Older age/frailty, diabetes, immunosuppression, renal disease or significant comorbidity.
• Stone, obstruction, urinary retention, vesicoureteral reflux or structural/functional abnormality.
• Recent hospitalization, urinary instrumentation/catheter or previous resistant organism.

Pathogenesis

• Most common route: ascending infection from periurethral/perineal flora.
• Female risk: short urethra + proximity to vagina/anus → easier ascent.
• Mechanism: bacterial adhesion → proliferation → epithelial invasion/inflammation → symptoms.

III. Microbiology and Clinical Features

Microbiology

• Uncomplicated cystitis: Escherichia coli most common, often > 80%.
• Other pathogens: Staphylococcus saprophyticus, Proteus, Klebsiella.
• Complicated UTI: E. coli, other Gram-negative rods, Enterococcus, Pseudomonas, resistant organisms.
• Catheter-associated UTI: Gram-negative rods, Enterococcus, Staphylococcus epidermidis, Candida/yeast.
• Urethritis/STI: Chlamydia trachomatis, Neisseria gonorrhoeae, Mycoplasma genitalium, Trichomonas.

Cystitis

• Symptoms: dysuria, frequency, urgency, suprapubic pain.
• May occur: hematuria, cloudy/foul-smelling urine.
• Fever/flank pain generally absent; if present → upper/systemic UTI.

Urethritis

• Symptoms: dysuria and frequency may mimic cystitis.
• Clues: urethral/cervical discharge, new sexual partner, pelvic symptoms, negative routine urine culture.

Pyelonephritis and Abscess

• Pyelonephritis: fever, chills, flank/back pain, costovertebral angle tenderness.
• Systemic symptoms: nausea, vomiting, malaise; may progress to sepsis.
• Renal/perinephric abscess: pyelonephritis-like picture + persistent fever despite appropriate antibiotics.

IV. Diagnosis

Simple Cystitis

• Clinical diagnosis: typical dysuria/frequency/urgency/suprapubic pain + no vaginal discharge/irritation + no systemic signs.
• Dipstick/urinalysis: leukocyte esterase or pyuria, nitrite, bacteriuria ± hematuria.
• Urine culture not always needed in classic uncomplicated cystitis.

When to Culture

• Pregnancy or suspected pyelonephritis/systemic UTI.
• Atypical symptoms, uncertain diagnosis, recurrent UTI, treatment failure or early recurrence.
• High resistance risk, complicated UTI, catheter-associated UTI or urinary tract abnormality.

Additional Tests

• NAAT/PCR: suspected chlamydia/gonorrhea or STI urethritis/cervicitis.
• Blood cultures: febrile patient, sepsis, complicated pyelonephritis.
• Ultrasound: obstruction, hydronephrosis, stone, pregnancy, recurrent infection, severe pyelonephritis.
• CT abdomen/pelvis: suspected abscess, obstruction/stone, severe disease or no response after about 72 hours.
• Urologic work-up: recurrent UTI with suspected stone, retention, reflux, fistula or anatomic abnormality.

V. Management

General Principles

• Symptomatic bacterial UTI: antimicrobial therapy according to site, severity, risk factors and local resistance.
• Hydration and analgesia/antipyretics as supportive care.
• Adjust antibiotics to culture and susceptibility when available.
• Do not use cystitis-only drugs such as nitrofurantoin/fosfomycin for pyelonephritis because renal tissue levels are inadequate.

Uncomplicated Cystitis in Non-Pregnant Women

• First-line examples: fosfomycin single dose, nitrofurantoin short course, pivmecillinam where available.
• Alternatives if susceptible/local resistance acceptable: trimethoprim/TMP-SMX or selected oral cephalosporin.
• Avoid routine fluoroquinolones for simple cystitis.
• Follow-up culture: not needed if symptoms resolve.

Pregnancy

• UTI in pregnancy is clinically important because cystitis/asymptomatic bacteriuria can progress to pyelonephritis and increase obstetric risk.
• Screen and treat asymptomatic bacteriuria according to local pregnancy protocol.
• Pregnancy-compatible options may include beta-lactams/cephalosporins, fosfomycin or nitrofurantoin depending on gestational age and contraindications.
• Pyelonephritis in pregnancy: usually hospital assessment, IV antibiotics, fluids, fetal/maternal monitoring.

Complicated / Catheter-Associated UTI

• Obtain urine culture before antibiotics if possible.
• Empiric therapy must cover likely resistant organisms and be adjusted to culture.
• Catheter-associated UTI: remove or replace catheter if still needed.
• Search for obstruction, stone, abscess or retention if severe or not improving.

Pyelonephritis

• Outpatient only if stable, non-pregnant, tolerates oral intake, no sepsis and reliable follow-up.
• Oral or IV antibiotic choice depends on severity, resistance risk and culture; severe disease needs IV therapy.
• Switch IV → PO after clinical improvement and afebrile state; complete appropriate total course.
• Renal/perinephric abscess: drainage + antibiotics as for complicated pyelonephritis.

Urethritis / STI Coverage

• Test with NAAT for Chlamydia trachomatis and Neisseria gonorrhoeae when suspected.
• Treat according to organism: gonorrhea → ceftriaxone-based regimen; chlamydia → doxycycline or pregnancy-compatible alternative.
• Treat/notify sexual partners and advise abstinence until treatment is completed and symptoms resolve.