In healthy people, urine is sterile bladder; no bacteria or other infectious microorganisms. The tube that carries urine from the bladder to outside the body (urethra) does not have bacteria or contains very little, so it is not possible to cause infection. However, any part of the urinary tract can be infected by various causes, and then a UTI occurs.

The importance of urinary tract infections lies not only in frequency but also on the risk posed to cause other disorders such as spread of infection, progressive and irreversible renal injury and relapse, the treatment and prevention are often difficult.

We can distinguish different types of urinary tract infections:

• Bacteriuria:  Bacteria in the urine, which may be asymptomatic, if two consecutive urine cultures are positive in a patient without symptoms.
• Lower urinary tract infections (UTI) include cystitis (bladder infection), urethritis (infection of the urethra), prostatitis (prostate infection) and orchitis (infection of the ducts responsible for the formation and excretion semen).
• Infections of the upper urinary tract  includes, among other conditions, acute pyelonephritis; in these cases the infection is at one or both kidneys.
• Uncomplicated urinary tract infections:  in patients with a structurally and functionally normal urinary tract. Includes cystitis and uncomplicated pyelonephritis in young women without other pathologies.
• Complicated urinary tract infections:  on urinary tract anatomical abnormalities or functioning, individuals with metabolic disorders, immunosuppression, or involving unusual or resistant pathogens. Urinary tract infections in children, boys and pregnant should be considered complicated.
• Recurrent urinary tract infections: it  may be relapses (same causative agent) or reinfection (different causative agent).
• Chronic urinary infection:  persistence of the same microorganism for months or years, with recurrence after treatment.

Over 95% of urinary tract infections are monomicrobial (one organism), and 5% of cases the infection is polymicrobial.  Escherichia coli  is the most common pathogen (80% of outpatient and 50% of those produced in the hospital environment).  S. saprophyticus  is the second agent in order of frequency (5-15%) in women 15-25 years, especially during the summer; followed other Enterobacteriaceae (Proteus, Klebsiella …).

In most urinary tract infections, the bacteria reach the bladder through the urethra. And from the bladder can ascend to the kidneys, producing calls pielonefriti s.

Among women prone to cystitis, microorganisms residing in the intestine colonize the genital area and the distal urethra before and during episodes of infection.

This genital colonization may be due to alteration of normal vaginal microflora due to the intake of antibiotics, other genital infections, or use of certain contraceptives such as spermicides, as well as to friction in the urethra during sexual intercourse. These are, in short, some of the  most common causes of urinary tract infections:

• Gender and sex:  the female urethra seems particularly prone to bacterial colonization by its proximity to the anus, its short length (about 4 cm) and its mouth on the lips. Intercourse promotes the introduction of bacteria into the bladder and temporarily associated with the onset of cystitis. It should also be noted that voiding after intercourse reduces the risk of cystitis because it can enhance the elimination of bacteria introduced during intercourse. Also, the use of composite spermicides with a diaphragm or spermicide-coated condoms, modifies the normal bacterial flora of the genitourinary tract, and has been associated with an increase in urinary tract infections.
• Pregnancy:  UTI are detected in 2-8% of pregnant women. In addition, pregnant women are more susceptible to upper urinary infections because the ureters are more relaxed and move less, among other things. Probing, during or after birth, it also increases the number of infections.
• Obstruction:  any obstacle that interferes with urine flow (tumor, narrowing, enlargement of the prostate, kidney …) increases the frequency of infections.
• Changes in innervation  (nerves arrival) of the bladder.
• Vesicoureteral reflux:  is defined as the passage of urine from the bladder into the ureters and sometimes into the kidney, and occurs with urination or bladder pressure rises. Reflux is common in children with anatomic abnormalities of the urinary tract or in those with normal but infected system.
• Genetic factors  have been shown that women who have suffered recurrent infections are more cases of maternal history of UTI than women who have not suffered.

These are the most common urinary tract infections and their symptoms:

Cystitis

The basic clinical cystitis is the sudden sensation of having to urinate urgently, pain-burning when urinating, laincontinencia, and pain in the pubic area. However, it is not often you have a fever.

The urine loses its light color and can become smelly and bloody.

Urethritis

One should think of her when it comes to a young patient with painful urination, overlapping appearance, or more than one week, if there is a history of recent change of sexual partner, the couple had a urethritis, or is it of promiscuous. In women presents with increased vaginal discharge, and exudative men with urethral discharge.

Vaginitis

Vaginitis is characterized by abnormal vaginal discharge characteristics, pain during sex and genital itching. Usually there is no bacteria in the urine.

Acute Bacterial Prostatitis

High fever, chills and malaise. This type of prostatitis may be associated with symptoms of cystitis, symptoms of urethral obstruction (difficulty initiating urination, intermittent stream, postvoid dribbling), and pain or discomfort in the perineal region. On rectal examination the prostate is enlarged and painful.

Chronic Bacterial Prostatitis

Recurrent infection with the same organism. The initial event may be related to a history of urological manipulation (such as with diagnostic tests). Between episodes of infection may be discomfort in pelvis or perineum, painful urination, or asymptomatic bacteriuria. Not usually have previous episodes of acute prostatitis and rectal examination is normal.

Prostatodynia (chronic pelvic pain)

Pain or discomfort in the perineal region more than three months duration, which sometimes goes to the back of the pelvis, the rectum, the suprapubic area and the external genitalia. You may also have pain when urinating, frequent urination, and sometimes urgently, decreased urine flow, or the output of blood with semen. The DRE is also normal.

Pyelonephritis

The typical clinical fever, back pain and symptoms of acute urinary tract infection occurs in 60% of cases. It may also be accompanied by nausea, vomiting and even diarrhea. The pain may spread to other abdominal inguinal areas and up. Sometimes, symptoms of lower tract infection and fever precede the rest of the box pyelonephritis in one or two days.