Urinary Tract Infection
Infectious diseases

Author: Fabrizio Mele
Date: 19/02/2010


Urinary tract infection (UTI) refers to the presence of clinical signs and symptoms arising from the genitourinary tract plus the presence of one or more micro-organisms in the urine exceeding a threshold value for significance (10^5 colony-forming units/mL).

It is caused expecially by bacteria, mainly Escherichia coli , that subvert innate defenses by invading superficial umbrella cells and rapidly increasing in numbers to form intracellular bacterial communities, so those bacteria in biofilms build themselves into structures that are more firmly anchored in infected cells and are more resistant to immune system assaults and antibiotic treatments.

UTIs can envelope bladder (the most common, also called cystitis), renal parenchyma (called pyelonephritis), ureters and urethra.


Urinary tract infections are caused by germs, usually bacteria, originate from the rectal microbiota that enter and colonizate the urethra and then the bladder, causing ascending infection. They can also spread to the kidneys.
There is also an hematogenous infection, during a sepsis.
Our body has some defense mechanism to contrast this bacteria. For example, bladder wall is coated with various mannosylated proteins, such as Tamm-Horsfall proteins (THP), which interfere with the binding of bacteria to the uroepithelium. Moreover, the unbound bacteria are more easily removed when voiding.
Some conditions can increase the risk of UTI, such as diabetes (that reduces immunitary defense), advanced age (more antibiotic therapy, often without symptoms), urinary retention (brain or nerve disorders, PBH, narrowed urethra), urinary catheter (physically disturb the protective lining, allowing bacteria to invade the exposed epithelium), kidney stones, sexual activity, oral contraception and pregnancy. Women are more prone to UTIs than men because in females, the urethra is much shorter and closer to the anus than in males.


The symptoms of a bladder infection are different from those of a kidney infection.
During a cystitis the patient can accuse:
* frequent urination,
* nocturia,
* dysuria,
* suprapubic pain,
* pyuria,
* hematuria,
* low-mild fever,
* cloudy urine,
* urinary incontinence.
But, it can also be asymptomatic.
For pyelonephritis, the main symptoms are:
* the bladder infection’s symptons,
* vomiting and general disorder,
* back pain,
* abdominal pain,
* shaking chills,
* high spiking fever and extreme fatigue.


Diagnosis is essentially clinical, but it can be confirmed by:
* urinalysis, to look for white blood cells, red blood cells, bacteria, and to test for certain chemicals, such as nitrites in the urine;
* urine culture - clean catch may be done to identify the bacteria in the urine to make sure the correct antibiotic is being used for treatment;
* blood panel and a blood culture may be done if sepsi;
* urea and creatinine measurements may be performed to assess whether renal function has been affected.
A negative urine test can also suggest the presence of unusual bacteria (Chlamydia trachomatis or Neisseria gonorrheae) or viruses causing symptoms of UTI.


Urinary tract infections need a mirate treatment, after urinocoltures and antibiograms, and it is suggested to correct risk factors.
UTIs can be separated into uncomplicated UTIs, uncomplicated pyelonephritis, and complicated UTIs.
Uncomplicated UTIs can be treated with oral antibiotics such as trimethoprim, cephalosporins, nitrofurantoin, or a fluoroquinolone (e.g., ciprofloxacin or levofloxacin). The guide lines recommend to take Trimethoprim/sulfamethoxazole for seven day, but a three-day treatment is usually all that is needed.
In pyelonephritis, intravenous antibiotics may be indicated in firsts days, and then oral antibiotics (quinolones, amynoglicosides and beta-lactam).
A urinary tract infection is uncomfortable, but treatment is usually successful. Symptoms of a cystitis usually disappear within 24 - 48 hours after treatment begins. If you have a kidney infection, it may take 1 week or longer for your symptoms to go away.
If the infection is complicated, it need more days of intravenous therapy, with quinolones, beta-lactam, amynoglicosides, and hospitalization.
Some complicated UTIs are recurrent (three or more episodes over one year). Patients with recurrent UTIs may need further investigation. This may include ultrasound scans of the kidneys and bladder or intravenous urography. It is also important to exclude interstitial cystitis.


People with recurrent UTIs can follow some measures to reduce the incidence of infections, for example:
* do not restrain urine;
* drink at least two liters;
* cleaning the urethral meatus with an antiseptic ointment;
* use of low-dose once-daily or post-coital antimicrobials;
* take cranberry juice or tablets ;
* intravaginal application of topical estrogen cream for post-menopausal women;
* acupuncture;
* Foley Catheter from clogging with biofilm to prevent stasis of urine in the bladder.


MedlinePlus Medical Encyclopedia: Urinary tract infection – adults

Wikipedia Encyclopedia: Urinary tract infection

Harrison’s Principles of Internal Medicine 17^ edition: Part 12. Disorders of the Kidney and Urinary Tract: Chapter 282 Urinary Tract Infections, Pyelonephritis, and Prostatitis

Martina Ferraresi
Fabrizio Mele

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