Urinary tract infection (overview)

Urinary tract infection (UTI) refers to microbial infection affecting any part of the urinary tract, including the urethra, bladder, ureters, kidneys, and surrounding structures. UTIs are among the most common bacterial infections encountered in clinical practice and may affect individuals of all ages. They may involve the lower urinary tract (cystitis) or the upper urinary tract (pyelonephritis). UTIs can be classified as uncomplicated or complicated depending on the presence of structural or functional abnormalities of the urinary tract and patient-specific risk factors.

An uncomplicated UTI typically occurs in a healthy, non-pregnant woman of reproductive age with a normal urinary tract. All other UTIs, including those occurring in men, pregnant women, children, elderly individuals, catheterized patients, and patients with urinary tract abnormalities, should be considered complicated.

The most common causative organisms in Tanzania include Escherichia coli, Klebsiella pneumoniae, Proteus species, and Staphylococcus aureus.

Epidemiology

UTIs are among the most frequently diagnosed bacterial infections worldwide. Women are more commonly affected than men due to anatomical factors such as a shorter urethra. The incidence is particularly high among sexually active women, pregnant women, young children, elderly individuals, and patients with urinary tract abnormalities or indwelling urinary catheters.

Recurrent UTIs are common and contribute significantly to healthcare utilization and antimicrobial use.

Risk factors

General risk factors

• Female sex

• Sexual activity

• Pregnancy

• Previous history of UTI

• Poor perineal hygiene

• Urinary tract obstruction

• Urinary stones

• Vesicoureteric reflux

• Neurogenic bladder

• Diabetes mellitus

• Immunosuppression

• Chronic kidney disease

• Indwelling urinary catheter

• Congenital urinary tract abnormalities

• Benign prostatic hyperplasia

• Advanced age

Pathophysiology

Most UTIs occur through ascending infection. Uropathogenic bacteria colonize the periurethral region and ascend through the urethra into the bladder. If untreated, infection may spread through the ureters to the kidneys, causing pyelonephritis.

Host defense mechanisms including urine flow, urinary pH, mucosal immunity, and bladder emptying normally prevent infection. Impairment of these mechanisms increases susceptibility to bacterial colonization and infection.

Clinical presentation

Clinical manifestations vary according to the site and severity of infection.

Lower urinary tract infection (cystitis)

Infection is confined primarily to the bladder and urethra.

Upper urinary tract infection (pyelonephritis)

Infection extends to the renal pelvis and renal parenchyma.

Catheter-associated urinary tract infection (CAUTI)

UTI occurring in a patient with a urinary catheter currently in place or removed within the preceding 48 hours.

Urosepsis

A severe systemic infection resulting from a urinary tract source accompanied by organ dysfunction.

Symptoms

Symptoms depend on the affected portion of the urinary tract and may include:

• Dysuria

• Urinary frequency

• Urinary urgency

• Suprapubic discomfort

• Flank pain

• Fever

• Chills

• Nausea

• Vomiting

• Haematuria

• Foul-smelling urine

• Confusion in elderly patients

Clinical signs

• Fever

• Suprapubic tenderness

• Costovertebral angle tenderness

• Tachycardia

• Hypotension in severe infection

• Dehydration

• Altered mental status in severe disease

• Signs of sepsis in advanced cases

Diagnostic criteria

The diagnosis of UTI is based on:

• Compatible clinical symptoms and signs

• Evidence of pyuria on urinalysis or urine microscopy

• Positive urine culture when available

A diagnosis is strongly supported by:

• Positive leukocyte esterase

• Positive nitrite test

• Urine microscopy showing more than 8–10 white blood cells per high-power field

• Significant bacterial growth on urine culture

Investigations

Urinalysis

• Leukocyte esterase

• Nitrite test

• Protein

• Glucose

• pH assessment

Urine microscopy

• White blood cells

• Red blood cells

• Bacteria

• Casts where indicated

Urine culture and antimicrobial susceptibility testing

Quantitative urine culture remains the gold standard for diagnosis.

Blood investigations

• Full blood count

• Serum creatinine

• Serum electrolytes

• Blood cultures in severe infection or suspected urosepsis

Imaging studies

• Ultrasound of kidneys and pelvis

• CT scan when indicated

• Additional urological investigations in recurrent or complicated infections

Special investigations

• Urinary lipoarabinomannan (LAM) testing in suspected genitourinary tuberculosis

Management

Management depends on the site, severity, and classification of infection.

Non-pharmacological treatment

• Ensure adequate hydration

• Encourage regular bladder emptying

• Encourage urination after sexual intercourse

• Maintain good perineal hygiene

• Remove unnecessary urinary catheters

• Correct underlying urinary tract abnormalities where possible

Pharmacological treatment

Treatment should be guided by:

• Severity of infection

• Patient characteristics

• Local antimicrobial susceptibility patterns

• Culture and sensitivity results where available

Specific treatment regimens are described in the following disease-specific chapters:

• Acute cystitis (lower urinary tract infection)

• Acute pyelonephritis (upper urinary tract infection)

• Catheter-associated urinary tract infection (CAUTI)

• Urosepsis

Management according to underlying cause

Urinary tract obstruction

• Relieve obstruction

• Treat infection

• Refer for definitive urological management

Urinary catheter

• Remove or replace catheter where appropriate

• Treat infection according to culture results

Urinary stones

• Treat infection

• Manage stones definitively

Vesicoureteric reflux

• Long-term follow-up

• Surgical correction where indicated

Diabetes mellitus

• Optimize glycaemic control

• Treat infection promptly

Referral

Refer patients who have:

• Suspected pyelonephritis

• Recurrent UTIs

• Urinary tract obstruction

• Urinary stones

• Structural urinary tract abnormalities

• Urosepsis

• Treatment failure

• Significant renal impairment

• Pregnancy with complicated UTI

• Severe infection requiring intravenous antibiotics

Complications

• Acute pyelonephritis

• Renal abscess

• Perinephric abscess

• Recurrent infection

• Renal scarring

• Chronic kidney disease

• Urosepsis

• Septic shock

• Pregnancy complications

• Death in severe untreated infection

Prognosis

The prognosis is generally excellent with early diagnosis and appropriate antimicrobial therapy. Delayed treatment, recurrent infections, structural abnormalities, or immunosuppression increase the risk of complications and long-term renal damage.

Prevention

• Adequate fluid intake

• Good perineal hygiene

• Prompt treatment of urinary symptoms

• Avoid unnecessary catheterization

• Early removal of urinary catheters

• Proper catheter care

• Control of diabetes mellitus

• Management of urinary tract abnormalities

• Urination after sexual intercourse

• Regular follow-up for patients with recurrent infections