A urinary tract infection ( UTI ) is a bacterial infection that affects any part of the urinary tract. The main etiologic agent is Escherichia coli. Although urine contains a variety of fluids, salts, and waste products, it does not usually have bacteria in it. When bacteria get into the bladder or kidney and multiply in the urine, they may cause a UTI.

The most common type of UTI is acute cystitis often referred to as a bladder infection. An infection of the upper urinary tract or kidney is known as pyelonephritis, and is potentially more serious. Although they cause discomfort, urinary tract infections can usually be easily treated with a short course of antibiotics. Symptoms include frequent feeling and/or need to urinate, pain during urination, and cloudy urine.

The most common symptoms of a bladder infection are burning with urination ( dysuria), frequency of urination, an urge to urinate, without vaginal discharge or significant pain.

The symptoms of urinary tract infections may vary with age and the part of the urinary system that was affected. In young children, urinary tract infection symptoms may include diarrhea, loss of appetite, nausea and vomiting, fever and excessive crying that cannot be resolved by typical measures. Older children on the other hand may experience abdominal pain, or incontinence. Lower urinary tract infections in adults may manifest with symptoms including hematuria (blood in the urine), inability to urinate despite the urge and malaise.

Other signs of urinary tract infections include foul smelling urine and urine that appears cloudy.

Depending on the site of infection, urinary tract infections may cause different symptoms. Urethritis, meaning only the urethra has been affected, does not usually cause any other symptoms besides dysuria. If the bladder is however affected (cystitis), the patient is likely to experience more symptoms including lower abdomen discomfort, low-grade fever, pelvic pressure and frequent urination all together with dysuria. Infection of the kidneys (acute pyelonephritis) typically causes more serious symptoms such as chills, nausea, vomiting and high fever.

Whereas in newborns the condition may cause jaundice and hypothermia, in the elderly, symptoms of urinary tract infections may even include lethargy and a change in the mental status, signs that are otherwise nonspecific.

Sexual activity

In young sexually active women, sex is the cause of 75???90% of bladder infections, with the risk of infection related to the frequency of sex. The term "honeymoon cystitis" has been applied to this phenomenon of frequent UTIs during early marriage. In post menopausal women sexual activity does not affect the risk of developing a UTI.

Gender

Women are more prone to UTIs than men because in females, the urethra is much closer to the anus than in males and they lack the bacteriostatic properties of prostatic secretions. UTI's more commonly progress to bladder infections in females due to the much shorter length of the female urethra. Among the elderly, UTI frequency is roughly equal proportions in women and men. This is due, in part, to an enlarged prostate in older men. As the gland grows, it obstructs the urethra, leading to increased difficulty in micturition. Because there is less urine flushing the urethra, there is a higher incidence of colonization.

Urinary catheters

Urinary catheters are a risk factor for urinary tract infections. The risk of an associated infection can be decreased by only catheterizing when necessary, using aseptic technique for insertion, and maintaining unobstructed closed drainage of the catheter.

Genetics

A predisposition for bladder infections may run in families.

Others

Other risk factors include diabetes , sickle-cell disease, or anatomical malformations of the urinary tract such as prostate enlargement.

While ascending infections are generally the rule for lower urinary tract infections and cystitis, the same is not necessarily true for upper urinary tract infections like pyelonephritis which may originate from a blood born infection .

The most common organism implicated in UTIs (80???85%) is E. Coli,

The bladder wall is coated with various mannosylated proteins, such as Tamm-Horsfall proteins (THP), which interfere with the binding of bacteria to the uroepithelium. As binding is an important factor in establishing pathogenicity for these organisms, its disruption results in reduced capacity for invasion of the tissues. Moreover, the unbound bacteria are more easily removed when voiding. The use of urinary catheters (or other physical trauma) may physically disturb this protective lining, thereby allowing bacteria to invade the exposed epithelium.

During cystitis, uropathogenic Escherichia coli (UPEC) subvert innate defenses by invading superficial umbrella cells and rapidly increasing in numbers to form intracellular bacterial communities (IBCs). By working together, 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 This is often the cause of chronic urinary tract infections.

The following are measures that studies suggest may reduce the incidence of urinary tract infections.

• A prolonged course (six months to a year) of low-dose antibiotics (usually nitrofurantoin or TMP/SMX) is effective in reducing the frequency of UTIs in those with recurrent UTIs.

• Cranberry (juice or capsules) may decrease the incidence of UTI in those with frequent infections. Long term tolerance however is an issue.

• For post-menopausal women intravaginal application of topical estrogen cream can prevent recurrent cystitis. This however is not as useful as low dose antibiotics.

• Studies have shown that breastfeeding can reduce the risk of UTIs in infants.

A number of measures have not been found to affect UTI frequency including: the use of birth control pills or condoms, voiding after sex, the type of underwear used, personal

hygiene methods used after voiding or defecating, and whether one takes a bath or shower.

In straight forward cases a diagnosis may be made and treatment given based on symptoms alone without further laboratory confirmation.

Urine culture showing a quantitative count of greater than or equal to 10³ colony forming units (CFU) per mL of a typical urinary tract organism along with antibiotic sensitives is useful to guide antibiotic choice.

Most cases of lower urinary tract infections in females are benign and do not need exhaustive laboratory work-ups. However, UTI in young infants may receive some imaging study, typically a retrograde urethrogram, to ascertain the presence/absence of congenital urinary tract anomalies. All males with a confirmed UTI should be investigated further. Specific methods of investigation include x-ray, nuclear medicine, MRI , DMSA and CAT scans.

Differential

If the urine culture is negative:

• symptoms of urethritis may point at Chlamydia trachomatis or Neisseria gonorrheae infection.

• symptoms of cystitis may point at interstitial cystitis.

• in men, prostatitis may present with dysuria.

The presence of bacteria in the urinary tract of older adults, without symptoms or signs of infection, is a well recognized phenomenon which may not require antibiotics. This is usually referred to as asymptomatic bacteriuria. The overuse of antibiotics in the context of bacteriuria among the elderly is a concerning issue.

Uncomplicated

Uncomplicated UTIs can be diagnosed and treated based on symptoms alone.

A three-days treatment with trimethoprim, TMP/SMX, or a fluoroquinolone is usually sufficient while nitrofurantoin requires 7 days. Trimethoprim is often recommended to be taken at night to ensure maximal urinary concentrations to increase its effectiveness. While trimethoprim/sulfamethoxazole was previously internationally used (and continues to be used in the U.S. and Canada); the addition of the sulfonamide gives little additional benefit compared to the trimethoprim component alone. It is responsible however for a high incidence of mild allergic reactions and rare but potentially serious complications. For simple UTIs children often respond well to a three-day course of antibiotics.

Pyelonephritis

Pyelonephritis is treated more aggressively than a simple bladder infection using either a longer course of oral antibiotics or intravenous antibiotics. Regimens vary, and include SMX/TMP and fluorquinolones. In the past, they have included aminoglycosides (such as gentamicin) used in combination with a beta-lactam, such as ampicillin or ceftriaxone. These are continued for 48 hours after fever subsides.

If there is a poor response to IV antibiotics (marked by persistent fever, worsening renal function), then imaging is indicated to rule out formation of an abscess either within or around the kidney, or the presence of an obstructing lesion such as a stone or tumor.

Recurrent

Women with recurrent simple UTIs may benefit from self-treatment upon occurrence of symptoms with medical follow up only if the initial treatment fails.

Bladder infections are most common in young women with 10% of women getting an infection yearly and 60% having an infection at some point in their life.

According to the 1997 National Ambulatory Medical Care Survey and National Hospital Ambulatory Medical Care Survey, urinary tract infection accounted for nearly 7 million office visits and 1 million emergency department visits, resulting in 100,000 hospitalizations.

Nearly 1 in 3 women will have had at least 1 episode of urinary tract infections requiring antimicrobial therapy by the age of 24 years. The risk of urinary tract infection increases with increasing duration of catheterization. In non-institutionalized elderly populations, urinary tract infections are the second most common form of infection, accounting for nearly 25% of all infections.

The condition rarely occurs in men who are younger than 50 years old and who did not undergo any genitourinary procedure. However, the incidence of urinary tract infections in men tends to rise after the age of 50.

According to statistics from 1990, the prevalence of urinary tract infections in pre-school and school girls was 1% to 3%, nearly 30-fold higher than that in boys. Also, the statistics from the same year show that approximately 5% of girls will develop at least one urinary tract infection in their school years.

In what concerns the symptoms of the condition, bacteriuria appears to increase in prevalence with age in women, still being 50 times greater than the one in males. It is estimated that bacteriuria will be experienced by 20 to 50% of older women and 5 to 20% of older men.

Children with recurrent UTIs maybe treated with preventative antibiotics which decrease the rate of microbiological recurrence but not symptomatic recurrence. These conclusion must be viewed in light of the poor quality of evidence available.

• NIH articles on Urinary Tract Infections in Adults and in Children .

• Urinary Tract Infection Video