UTI

Term

Definition

UTI Classification by anatomical site

Lower UTIs (urethritis, cystitis, prostatitis) and Upper UTIs (ureteritis, pyelonephritis).

Urethritis

Inflammation of the urethra; lower UTI.

Cystitis

Bladder infection; most common lower UTI.

Prostatitis

Prostate inflammation/infection in males; lower UTI.

Pyelonephritis

Kidney infection; upper UTI; often more severe.

Most common cause of uncomplicated UTIs

Escherichia coli (E. coli) — responsible for 75-95% of cases.

Second most common cause of UTI in young sexually active women

Staphylococcus saprophyticus (gram-positive).

Proteus mirabilis

Gram-negative organism that produces urease → alkaline urine → formation of struvite stones.

Pseudomonas aeruginosa

Gram-negative organism common in catheterized and immunocompromised patients; notoriously multidrug resistant (MDR).

Enterococcus faecalis

Gram-positive organism associated with elderly patients and structural urinary abnormalities.

Key pathogens in lower UTI

E. coli, Staphylococcus saprophyticus, Klebsiella pneumoniae, Proteus mirabilis.

Key pathogens in pyelonephritis

Often E. coli; more Klebsiella, Enterococcus, or Pseudomonas in complicated cases.

Most common fungal UTI pathogen

Candida albicans.

Fungal UTI risk factors

Prolonged antibiotic use, diabetes mellitus, indwelling catheters.

Viral UTI pathogens

Adenovirus (hemorrhagic cystitis), BK virus (nephropathy in transplant recipients).

Parasitic UTI pathogen

Schistosoma haematobium — endemic in parts of Africa (Ghana); causes terminal hematuria, bladder fibrosis, increased risk of bladder cancer.

Primary mechanism of UTI infection

Ascending infection: colonization of periurethral area → ascension into bladder → cystitis → further ascent → pyelonephritis.

Bacterial virulence mechanisms

Adhesins (fimbriae) prevent washout by urine; biofilm formation protects bacteria from antibiotics; toxins damage uroepithelium.

Host defense mechanisms against UTIs

Continuous urine flow, low urine pH, immune responses, vaginal flora (Lactobacillus inhibits pathogen growth).

Complicated UTI factors

Obstruction, stones, catheters, vesicoureteral reflux, pregnancy, diabetes, immunosuppression.

Lifetime risk of UTI in women

50-60%.

Lifetime risk of UTI in men

Significantly lower (until older age).

High-risk UTI groups

Females (short urethra), pregnant women, diabetics, elderly patients, catheterized individuals.

CAUTI

Catheter-associated UTI; leading cause of secondary bacteremia in hospitalized patients.

Cystitis symptoms

Dysuria (painful urination), urinary urgency and frequency, suprapubic discomfort, occasional hematuria.

Pyelonephritis symptoms

Fever (>38°C), flank pain, nausea/vomiting, costovertebral angle tenderness, possible sepsis.

Asymptomatic bacteriuria

Positive urine culture (>10⁵ CFU/mL) without symptoms. Treat only in pregnancy or before urologic procedure.

Urinalysis findings in UTI

Leukocyte esterase (indicates WBCs), nitrites (suggest gram-negative bacteria).

Microscopy findings in UTI

Pyuria (>5-10 WBC/HPF), bacteriuria.

Gold standard for UTI diagnosis

Urine culture. Significant bacteriuria = ≥10⁵ CFU/mL.

Imaging indications in UTI

Recurrent infections, suspected obstruction, complicated UTIs.

General principles of UTI therapy

Initiate empiric therapy based on local resistance patterns; de-escalate after culture results; consider patient age, pregnancy status, renal function, allergy history.

Fluoroquinolone caution

Avoid for uncomplicated cystitis unless no alternatives due to side effects and resistance.

First-line agent for uncomplicated cystitis

Nitrofurantoin 100 mg BID x 5 days. Advantages: low resistance, concentrates in urine.

Nitrofurantoin mechanism

Inhibits bacterial ribosomes and multiple enzymes (bacteriostatic).

Nitrofurantoin adverse effects

GI upset, pulmonary fibrosis (chronic use), peripheral neuropathy, hemolysis (G6PD deficiency).

Nitrofurantoin interactions

Antacids (↓ absorption); probenecid (↓ renal excretion).

Nitrofurantoin counselling

Take with food to reduce nausea; urine may turn brown (harmless).

TMP-SMX dose for cystitis

160/800 mg BID x 3 days. Use only if local resistance <20%.

TMP-SMX mechanism

Sequential folate synthesis block (bactericidal).

TMP-SMX adverse effects

Rash, hyperkalemia (TMP blocks amiloride-sensitive Na channels), Stevens-Johnson syndrome, myelosuppression.

TMP-SMX interactions

Warfarin (↑ INR), phenytoin, sulfonylureas (hypoglycemia), ACEi/ARB (↑ K+).

TMP-SMX counselling

Hydrate well; report rash or mouth sores.

Fosfomycin dose for cystitis

3 g single dose. Useful for multidrug-resistant organisms.

Fosfomycin mechanism

Inhibits enolpyruvyl transferase (cell wall synthesis).

Fosfomycin adverse effects

Diarrhea, headache, vaginitis.

Fosfomycin interaction

Metoclopramide (↓ absorption); no major CYP interactions.

Second-line options for cystitis

Beta-lactams: amoxicillin-clavulanate, cephalexin 500 mg BID x 7 days. Less effective → longer duration required.

Cephalexin mechanism

PBP binding → cell wall lysis.

Cephalexin adverse effects

Diarrhea, rash, hypersensitivity (cross-react with penicillin ~10%).

Cephalexin interaction

Probenecid (↑ levels).

Complicated UTI/pyelonephritis outpatient treatment (mild/moderate)

Ciprofloxacin 500 mg BID x 7 days OR Levofloxacin 750 mg daily x 5-7 days. Alternatives: TMP-SMX 160/800 mg BID x 14 days, or cephalosporins (cefdinir, cefpodoxime).

Complicated UTI/pyelonephritis inpatient treatment (severe)

IV antibiotics: Ceftriaxone 1 g q24h, Piperacillin-tazobactam 3.375 g q6h, or Ertapenem 1 g q24h. Step-down to oral after fever resolution (48-72h).

Ciprofloxacin mechanism

DNA gyrase/topo IV inhibitor (bactericidal).

Ciprofloxacin adverse effects

Tendinitis/rupture, QT prolongation, C. diff, photosensitivity.

Ciprofloxacin interactions

Theophylline (↑ toxicity), warfarin, Mg/Al/Fe/Zn (chelation).

Ciprofloxacin counselling

Stop immediately if tendon pain/swelling; avoid exercise.

When to treat asymptomatic bacteriuria

Pregnant women, before urologic surgery (e.g., TURP), renal transplant recipients (first month).

When NOT to treat asymptomatic bacteriuria

Elderly, diabetics, spinal cord injury (no benefit, increases resistance).

UTI in pregnancy: safe antibiotics

Nitrofurantoin (avoid near term — hemolysis risk in G6PD-deficient newborn), cephalexin, amoxicillin-clavulanate, fosfomycin.

UTI in pregnancy: avoid

TMP-SMX (1st & 3rd trimester — folate antagonist, kernicterus risk), fluoroquinolones (cartilage toxicity).

CAUTI treatment

Remove/replace catheter before antibiotics. Treat based on culture. Duration: 7 days (if prompt removal) or 10-14 days (if catheter remains).

Patient counselling: complete course

Complete full course (even if symptoms resolve) — except fosfomycin (single dose).

Prevention: hydration

2-3 L water/day (reduces recurrence).

Prevention: voiding habits

Void after intercourse; avoid delaying urination.

Cranberry products mechanism

Proanthocyanidins prevent bacterial adhesion. Modest benefit in premenopausal women. NOT a replacement for antibiotics.

Post-coital prophylaxis indication

Single dose TMP-SMX, nitrofurantoin, or cephalexin if ≥3 UTIs/year related to intercourse.

Continuous prophylaxis indication

≥3 symptomatic UTIs/6 months or ≥4/year. Regimen: Nitrofurantoin 50-100 mg daily or TMP-SMX half-strength daily for 6 months.

Vaginal estrogen in postmenopausal women

Restores lactobacilli; prevents UTIs.

Therapeutic monitoring

Symptom resolution (dysuria improves by 48h). Test of cure only in pregnancy, recurrent, or persistent symptoms.

Nitrofurantoin safety monitoring (>6 months)

Pulmonary function tests, LFTs.

TMP-SMX safety monitoring (>2 weeks)

CBC, serum creatinine, potassium.

Fluoroquinolone safety monitoring

Monitor for neuropsychiatric effects (confusion, agitation).

When to seek immediate care

Worsening symptoms or no improvement by 48-72h (need culture); fever, flank pain, vomiting (pyelonephritis); signs of adverse reaction (severe diarrhea, rash, tendon pain).

Beta-lactam IV adverse effects (prolonged)

Diarrhea, neutropenia, interstitial nephritis.

Beta-lactam IV interaction

Methotrexate (↓ excretion).

TMP-SMX hyperkalemia mechanism

TMP blocks amiloride-sensitive sodium channels in collecting duct → reduces potassium excretion.

Nitrofurantoin pulmonary fibrosis risk

With chronic use (>6 months) — monitor pulmonary function.

Leukocyte esterase

Urinalysis marker indicating presence of white blood cells (pyuria).

Nitrites on urinalysis

Suggest gram-negative bacteria (convert nitrates to nitrites).