Back
ditki Logo
medical & biological sciences

Urinary Tract Infections for the USMLE Step 2

Start your One-Week Free Trial
Already subscribed? Log in »
Urinary Tract Infections for the USMLE Step 2 Exam
  • Definition:
    • Urinary tract infections (UTIs) are microbial infections of the urinary tract, affecting the urethra, bladder, ureters, or kidneys. They are classified into:
    • Lower UTI (Cystitis): Infection confined to the bladder and urethra.
    • Upper UTI (Pyelonephritis): Infection that involves the kidneys.
  • Etiology:
    • The most common causative organism is Escherichia coli (75-95% of cases). Other pathogens include:
    • Staphylococcus saprophyticus (especially in sexually active women).
    • Proteus mirabilis, Klebsiella pneumoniae, and Enterococcus in complicated or healthcare-associated UTIs.
    • Fungal UTIs (primarily caused by Candida) are more frequent in immunocompromised patients or those with indwelling catheters.
  • Risk Factors:
    • Female Anatomy: The shorter female urethra increases the risk of UTI.
    • Sexual Activity: Increases the likelihood of bacteria entering the urethra.
    • Postmenopausal Women: Loss of estrogen leads to changes in vaginal flora, increasing susceptibility.
    • Urinary Stasis: Conditions like benign prostatic hyperplasia (BPH), kidney stones, or vesicoureteral reflux impair urinary drainage.
    • Diabetes: Hyperglycemia reduces immune function, increasing infection risk.
    • Indwelling Catheters: Provide a route for bacteria to enter the bladder.
  • Clinical Features:
    • Lower UTI (Cystitis):
    • Dysuria: Pain or burning during urination.
    • Urinary frequency and urgency: Frequent need to urinate with urgency but small urine volumes.
    • Suprapubic pain: Discomfort over the bladder.
    • Hematuria: Blood in the urine may be present.
Cystitis urine output
    • Upper UTI (Pyelonephritis):
    • Fever and chills: Indicating systemic infection.
    • Flank pain: Pain in the costovertebral angle.
    • Nausea and vomiting: Gastrointestinal symptoms are common.
    • Signs of sepsis: Severe cases may present with hypotension or confusion, particularly in older adults.
  • Diagnosis:
    • Urinalysis:
    • Nitrites: Positive in gram-negative infections (e.g., E. coli).
    • Leukocyte esterase: Indicates the presence of white blood cells in the urine (pyuria).
    • Microscopy: Confirms bacteriuria and pyuria.
    • Urine Culture:
    • The gold standard for diagnosing UTI, especially in complicated or recurrent cases. A bacterial count ≥10⁵ CFU/mL is diagnostic.
    • Imaging:
    • Not typically needed for uncomplicated UTIs. In recurrent or complicated cases, renal ultrasound or CT scan may be used to evaluate for kidney stones, abscesses, or anatomical abnormalities.
  • Management:
    • Uncomplicated UTI:
    • Antibiotics:
    • First-line treatments include nitrofurantoin (5 days), trimethoprim-sulfamethoxazole (TMP-SMX) (3 days), or fosfomycin (single dose).
    • Fluoroquinolones (e.g., ciprofloxacin) are reserved for resistant cases or contraindications to first-line agents.
    • Symptomatic Relief:
    • Phenazopyridine can be used short-term for dysuria relief but is not a treatment for infection.
    • Hydration: Encouraging increased fluid intake may help flush bacteria from the urinary tract.
    • Complicated UTI:
    • Requires a longer course of antibiotics (7-14 days), tailored to the pathogen identified by culture.
    • Hospitalization may be necessary for patients with severe pyelonephritis, immunocompromised patients, or those showing signs of sepsis. Intravenous (IV) antibiotics (e.g., ceftriaxone or fluoroquinolones) are commonly used in severe cases.
    • Recurrent UTI:
    • Behavioral Modifications: Increased fluid intake, post-coital voiding, and avoiding spermicides are recommended.
    • Prophylactic Antibiotics: Low-dose antibiotics or post-coital antibiotics can be used in patients with frequent UTIs.
    • Pyelonephritis:
    • Requires empiric broad-spectrum antibiotics (e.g., IV ceftriaxone or oral fluoroquinolones), later tailored based on urine culture results.
    • Hospitalization is necessary for patients with severe infection, dehydration, or systemic symptoms.
  • Complications:
    • Acute Kidney Injury: Severe pyelonephritis can cause renal parenchymal damage.
    • Sepsis: Pyelonephritis can lead to urosepsis and septic shock if not treated promptly.
    • Chronic Pyelonephritis: Recurrent upper UTIs can result in renal scarring and chronic kidney disease (CKD).
Key Points
  • UTIs are commonly caused by E. coli, with cystitis affecting the bladder and pyelonephritis involving the kidneys.
  • Lower UTI presents with dysuria, frequency, and suprapubic pain, while upper UTI (pyelonephritis) presents with fever, flank pain, and systemic symptoms.
  • Diagnosis is based on urinalysis (positive nitrites and leukocyte esterase) and confirmed by urine culture.
  • First-line treatment for uncomplicated UTI includes nitrofurantoin or TMP-SMX. Complicated UTI requires longer treatment and possibly hospitalization.
  • Prevention strategies for recurrent UTIs include increased hydration, behavioral changes, and prophylactic antibiotics in select patients.

Related Tutorials