Urinary tract infection (UTI): causes, symptoms, diagnosis and treatment

Causes and risk factors

Most community-acquired UTIs are due to bacteria from the gut that enter the urinary system. The species Escherichia coli is the predominant pathogen in uncomplicated infections (E. coli). Other bacterial species can also cause infection; medical devices such as urinary catheters increase the chance of additional organisms. Certain behaviors and conditions raise the risk of infection, including sexual activity (sexual intercourse), being female (shorter urethra), pregnancy, urinary retention, anatomic abnormalities, and a family history of recurrent infections. Older adults and people with weakened immune systems are at higher risk for complicated courses.

Typical signs and symptoms

Symptoms depend on which part of the tract is infected. Lower tract infections commonly cause urinary urgency and frequency, a burning sensation when urinating (dysuria), and cloudy or strong-smelling urine. Upper tract or kidney involvement often produces fever, chills and flank or back pain (side and back pain) and may be accompanied by nausea. Young children and older adults may present atypically, with irritability, decreased appetite, confusion or nonspecific decline rather than the classic urinary complaints.

Diagnosis

Diagnosis is based on clinical features and urine testing. In many healthy, nonpregnant women with typical symptoms, clinicians may diagnose a UTI by history alone. When testing is used, a urinalysis can detect white blood cells, red blood cells and nitrites suggestive of bacterial infection; a urine culture identifies the specific organism and its antibiotic sensitivities. Recurrent, complicated or severe cases may prompt imaging or specialist referral.

Treatment and management

Antibiotics are the mainstay of treatment for bacterial UTIs. Choice of agent and duration depend on whether the infection is uncomplicated or complicated, the suspected organism and local patterns of antimicrobial resistance. Mild lower tract infections are often treated with short courses of oral antibiotics; kidney infections or patients who appear systemically unwell may require longer therapy or hospitalization and intravenous antibiotics. Supportive measures—fluid intake, analgesics and urinary adjuncts—can ease symptoms. For people with frequent recurrent infections, preventive strategies include behavioral measures, targeted prophylactic antibiotics or other medical approaches tailored by a clinician.

Prevention and important distinctions

Preventive advice commonly includes staying well hydrated, urinating after sexual activity, avoiding irritating feminine products and managing underlying urinary retention. Evidence for some popular measures, such as cranberry products, is mixed and should be discussed with a healthcare provider. Distinguishing an uncomplicated bladder infection from a complicated infection involving the kidneys or factors such as pregnancy, diabetes or structural urinary problems is important because management differs.

Complications and epidemiology

If untreated, a lower UTI can ascend to the kidneys and, rarely, spread into the bloodstream causing sepsis. Catheter-associated UTIs are a major cause of healthcare-associated infection. UTIs are especially common in women—about half of women experience a UTI at some point in life and roughly ten percent may develop one each year—while men are affected less frequently but more likely to have complicating factors when infected. Growing antimicrobial resistance has made appropriate diagnosis and targeted therapy increasingly important to preserve effective treatment options.

• When to seek care: high fever, severe flank pain, persistent vomiting, inability to tolerate fluids, signs of sepsis or symptoms that do not improve within 48–72 hours of initial therapy.
• Further reading: general clinical guidance and patient resources are available from health organizations and clinical societies (bacterial causes, kidney infection, symptom details, fungal causes).