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Urinary tract infection

A urinary tract infection (UTI) generally refers to any infection at any location of the urinary tract and is almost always bacterial. We distinguish upper UTI and lower UTI depending on the location of the infection.

Lower UTI is much more common and includes cystitis (most common) and possibly prostatitis. Cystitis is often technically accompanied by urethritis but we generally just call lower UTI "cystitis". Urethritis in isolation is usually a sexually transmitted infection and is not considered a UTI. Cystitis is causes dysuria, urinary urgency, and urinary frequency.

Upper UTI affects the renal pelvis and is called pyelonephritis. This is usually due to a lower UTI which has ascended. Pyelonephritis causes fever, chills, flank pain, nausea/vomiting, and tenderness at the costovertebral angle. Symptoms of cystitis may be absent.

Another important distinction is whether the UTI is uncomplicated or complicated. This classification is a bit different between guidelines and studies. The European Association of Urology classification is probably the most relevant for us:

  • Asymptomatic bacteriuria
    • Presence of bacteria in the urine without evidence (signs or symptoms) of infection
  • Uncomplicated UTI
    • A UTI (lower or upper) which is acute, sporadic, or recurrent and occurs in a non-pregnant woman with no known anatomical or functional abnormalities in the urinary tract
  • Complicated UTI
    • (All UTIs not considered uncomplicated according to the criteria above)
    • UTI in a male (it is controversial whether all UTIs in males are complicated)
    • UTI in a pregnant female
    • UTI in a person with an indwelling urinary catheter (catheter-associated UTI)
    • UTI in a person with anatomical or functional abnormalities in the urinary tract
    • UTI in a person with renal disease like kidney transplant or polycystic kidney disease
    • UTI in a person with immunocompromising disease such as uncontrolled diabetes mellitus

The above classification is intended to identify those cases where eradication of the infection will be more difficult; these are the "complicated UTIs". This warrants use of different antibiotics and management.

Asymptomatic bacteriuria refers to commensal colonisation of the urine. This may protect against superinfection with other microbes that cause UTI, and so asymptomatic bacteriuria should not be routinely treated except in certain subgroups. These include patients who are going to undergo urologic surgery of the urinary tract and pregnant women (controversial).

Urosepsis refers to sepsis originating from the urinary tract.

Recurrent UTI refers to ≥ 3 episodes of UTI within a year or ≥ 2 episodes within 6 months.

Epidemiology

Uncomplicated cystitis is a very common condition, and almost half of all women will experience at least one episode.

Etiology

Risk factors of UTI include:

  • Previous UTI
  • Female gender (due to their shorter urethra and the urethras proximity to the vagina)
  • Sexual activity (irritates the urethral meatus and may spread bacteria into the urethra)
  • Indwelling urinary catheter or ureteral stent
  • Structural or functional abnormality of the urinary tract which cause urinary stasis (stone, BPH, vesicoureteral reflux)
  • Postmenopause

Typical microbes include:

Clinical features

Lower UTI causes lower urinary tract symptoms like dysuria, urinary frequency, and urinary urgency. There may be suprapubic tenderness (as the bladder is tender). Fever and chills are not symptoms of lower UTI and are signs that the infection has ascended.

Upper UTI (pyelonephritis) causes fever, pain in the flank, chills, and tenderness at the costovertebral angle. There may be nausea/vomiting. Lower UTI symptoms may be absent.

In elderly, the presenting symptom may be delirium alone.

Diagnosis and evaluation

Uncomplicated lower UTI can be diagnosed clinically and does not require urine analysis or culture. In all other cases, a urine analysis should be performed. Evidence of leukocyturia and nitrite positivity on the urine dipstick is proof of bacteriuria, but nitrite is only positive in case of bacteria which convert nitrates to nitrites, which not all causative bacteria do. Urine should be sendt for bacterial culture. Blood culture is indicated in upper UTI.

If the UTI is complicated, an underlying disease should be sought and treated if necessary. CT or ultrasound of the urinary tract can show structural abnormalities or hydronephrosis, which is a sign of a complicating obstruction.

Management

Uncomplicated lower UTI is often self-limiting and antibiotics are therefore not obligatory. However, they do shorten the duration of the disease and improve symptoms earlier, so many opt for antibiotics rather than wait-and-see.

For complicated UTI or upper UTI, antibiotics are always indicated. Patients with severe UTI should be admitted for IV antibiotics, otherwise PO antibiotics are sufficient. Antibiotics should be chosen according to local guidelines depending on the local resistance patterns. In Norway for example, there is very little antibiotic resistance among common causative microbes, and so more narrow-spectrum antibiotics are used than elsewhere.

The European Association of Urology guidelines recommend nitrofurantoin, pivmecillinam, or fosfomycin for uncomplicated lower UTI and trimethoprim/sulfamethoxazol or third generation cephalosporins for uncomplicated upper UTI. For complicated UTI a combination of aminopenicillin with an aminoglycoside or a third generation cephalosporin intravenously is indicated.

If the patient worsens despite treatment, urinary obstruction should be ruled out. Pyelonephritis with obstruction (seen as hydronephrosis) is an urological emergency which can rapidly progress to urosepsis. Urgent urinary drainage with percutaneous nephrostomy or ureteral stent is indicated.

Prevention

Increased fluid intake, timely voiding, and voiding after sexual intercourse help reduce the recurrence rate. Not using urinary catheters more than necessary is also important to reduce UTIs.

For recurrent UTI, antibiotic prophylaxis with low-dose antibiotics may be used. In postmenopausal women, vaginal oestrogen replacement therapy may reduce recurrence.

Emphysematous pyelonephritis

Emphysematous pyelonephritis is a necrotising form of pyelonephritis where there is formation of gas in the kidney and perinephric tissue. It's very rare but is very severe with a 40-90% mortality. It almost exclusively occurs in people with uncontrolled diabetes mellitus. Wide spectrum antibiotics is indicated and percutaneous drainage should be considered.