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Emergency and Acute Medicine: Urinary Tract Infections (Adult)
Urinary tract infections (UTIs) are caused by colonization of urine with uropathogens and subsequent invasion of the genitourinary tract. They are defined by the presence of urinary symptoms along with significant bacterial counts (typically ≥10²–10⁵ CFU/mL) and pyuria. UTIs are extremely common, particularly in women, with a lifetime risk exceeding 50%. They are broadly classified into uncomplicated and complicated infections, as well as lower tract infections (cystitis) and upper tract infections (pyelonephritis).
Uncomplicated cystitis typically occurs in otherwise healthy, nonpregnant women aged 13–50 years who present with short-duration symptoms such as dysuria, urinary frequency, and urgency, without systemic features like fever or flank pain. In contrast, complicated cystitis includes infections in men, pregnant women, immunocompromised individuals, or those with structural or functional abnormalities of the urinary tract, recent instrumentation, or resistant organisms. Pyelonephritis represents infection of the renal parenchyma and presents with systemic symptoms such as fever, chills, flank pain, nausea, and vomiting, often accompanied by costovertebral angle tenderness. Severe cases may involve urosepsis or septic shock.
The pathogenesis usually involves ascending infection, where organisms colonize the periurethral area and ascend into the bladder and possibly the kidneys. The most common pathogen is Escherichia coli, responsible for 80–85% of infections. Other organisms include Staphylococcus saprophyticus, as well as Klebsiella, Proteus, Enterobacter, and Pseudomonas aeruginosa. Risk factors include sexual activity, use of spermicides or diaphragms, postmenopausal changes, incomplete bladder emptying, urinary incontinence, and instrumentation such as catheterization.
Clinically, lower urinary tract infections present with dysuria, urgency, frequency, hesitancy, suprapubic pain, and sometimes hematuria. Upper tract infections add systemic features such as fever, chills, flank pain, nausea, vomiting, and leukocytosis. Elderly patients may present atypically with altered mental status, anorexia, or functional decline rather than classic urinary symptoms.
Diagnosis relies primarily on urinalysis. Dipstick testing for leukocyte esterase and nitrites is a rapid and useful screening tool, with nitrites having high specificity for bacterial infection. Microscopy showing ≥10 white blood cells per mm³ supports the diagnosis. Urine culture is not always necessary in uncomplicated cases but is indicated in complicated infections, pyelonephritis, recurrent infections, treatment failure, or suspected resistant organisms.
The differential diagnosis includes appendicitis, diverticulitis, nephrolithiasis, pelvic inflammatory disease, prostatitis, urethritis, epididymitis, and vulvovaginitis. These should be considered particularly when symptoms are atypical or when patients do not respond to standard therapy.
Management depends on severity and classification. Stable patients with uncomplicated cystitis are typically treated with short-course oral antibiotics, usually for 3 days. First-line agents include nitrofurantoin, trimethoprim–sulfamethoxazole, and fluoroquinolones, although resistance patterns must be considered. Nitrofurantoin is often preferred due to lower resistance rates. Symptomatic relief can be provided with agents such as phenazopyridine for dysuria. For pyelonephritis, initial management may include intravenous fluids, analgesia, and parenteral antibiotics such as ceftriaxone or gentamicin, followed by oral therapy if the patient improves.
Pregnancy requires special consideration. Asymptomatic bacteriuria should be treated due to the high risk of progression to pyelonephritis and adverse pregnancy outcomes. Safe options include nitrofurantoin (avoiding first trimester if possible), amoxicillin, and fosfomycin. Trimethoprim–sulfamethoxazole should be avoided in early and late pregnancy, and fluoroquinolones are contraindicated.
Disposition depends on clinical stability. Patients who are well-appearing, able to tolerate oral therapy, and have no significant comorbidities may be discharged with follow-up. Admission is indicated for those with severe illness, inability to tolerate oral medications, unstable vital signs, immunosuppression, urinary obstruction, or failure of outpatient therapy.
Important clinical pearls include recognizing that asymptomatic bacteriuria is common in elderly patients and usually should not be treated unless symptomatic, except in specific populations such as pregnant women or those undergoing urologic procedures. Recurrent UTIs may require prophylactic strategies. Additionally, antibiotic resistance is increasing, making local resistance patterns important in guiding therapy.
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