Fernando L. Soldano

Urinary tract infections are a common cause of morbidity and can cause significant mortality. Careful diagnosis and treatment lead to a favorable resolution in most cases.

They comprise a wide variety of clinical entities whose common denominator is bacterial invasion of the renal parenchyma and / or its excretion routes.


Urinary infection : It is an inflammatory response of the urinary tract to bacterial invasion, which is usually associated with bacteriuria and pyuria.

Bacteriuria : It is the presence of bacteria in the urine, which is normally free of them, and they are not contaminating the skin, vagina or foreskin. Significant bacteriuria has a clinical connotation and is used to describe the number of bacteria in a suprapubic aspirate or catheterization sample. It can be symptomatic or asymptomatic.

Pyuria : It is the presence of leukocytes in the urine and generally indicates inflammation of the urinary epithelium secondary to infections, tuberculosis, stones or cancer.

Acute pyelonephritis : A clinical syndrome that presents with chills, fever, and low back pain, accompanied by bacteriuria and pyuria.

Chronic pyelonephritis : retracted kidney with scars, diagnosed by morphological, radiological or functional evidence of kidney disease, which may be postinfectious.

Cystitis : It is the inflammation of the bladder. It applies to a clinical syndrome that is usually associated with dysuria, frequency, urgency, and suprapubic pain of sudden onset.

Urethritis : It is the inflammation of the urethra. Difficult to diagnose in women. It is divided into uncomplicated, when it occurs in patients with structurally and functionally normal urinary tract. Complicated, it is an infection in a patient with a structural or functional abnormality that increases the probability of infections or reduces the effectiveness of treatment.

Reinfection : It is a recurrent infection with different bacteria from outside the urinary system.

Recurrence or relapse : It is a recurrent UTI caused by the same bacteria originated by a focus that is within the urinary system, for example, infected stone or prostate.

Antibacterial prophylaxis : It is the prevention of urinary reinfections through the administration of antibiotics.

Outpatient UTIs: These are urinary infections in non-hospitalized patients, generally their causative agents are common fecal bacteria (eg, Enterobacteriaceae, enterococcus faecalis or Staphylococcus epidermidis).

Nosocomial UTI : The one that occurs in hospitalized patients and is caused by pseudomonas and other multiresistant antimicrobial strains.


Urinary tract infections are divided into four categories: 1. Isolated infections, 2. Unresolved infections, 3. Recurrent infections or reinfections, and 4. Bacterial persistence.

  1. Primary infections or infections separated by at least 6 months from each other occur in 25 to 30% of women between 30 and 40 years old, but are rare in men with a normal urinary system.
  2. The term unresolved indicates that the initial treatment has been inadequate. The most common cause of this is because the infecting microorganisms are resistant to the antimicrobial selected to treat the infection. Other less common causes: development of bacterial resistance, more than one knowledge, rapid reinfection to a resistant germ, uremia, papillary necrosis x abuse of analgesics, staghorn calculus, poor taking of the indicated drugs, etc.
  3. The term recurrent urinary tract infections applies both to reinfections that come from outside the urinary system and to bacterial persistence in an intraurinary focus. The term reinfections occurs in more than 95% of infections in women.
  4. Bacterial persistence is when the germ persists after a time after having completed the appropriate therapeutic scheme. Causes: stones, chronic prostatitis, atrophic kidney, ureteral duplication, foreign bodies, papillary necrosis, etc.


Urinary tract infections are the result of uropathogen-host interactions.

Route of infection:

  1. Ascending: Most bacteria enter the urinary system from the fecal reservoir ascending through the urethra to the bladder, and from there it can ascend to the kidney.
  2. Hematogenous: It is rare, but it can occur in patients with bacteremia.
  3. Lymphatic: Rare, but can occur in intestinal infections or retroperitoneal abscess.

Urinary pathogens

Escherichia coli is the most common cause of UI, causing 85% of community-acquired infections and 50% of hospital UIs. Less frequent proteus, klebsiela, enterobacter, citrobacter, serratia, pseudomonas, s. epidermidis, etc. All this influenced by age, presence of DBT, catheters, individual immune status, congenital anomalies, etc.


A thorough interrogation directed to the urinary system and related symptoms, such as fever, burning and urinary urgency, dysuria, tenesmus, lumbar pain or in any part of the urinary system, general malaise, decay, changes in the smell of urine, presence of hematuria, etc., antecedents such as DBT, lithiasis, surgeries, malformations, previous infectious episodes, HIV, etc. should also be ruled out.

After the same, the physical examination should not be omitted, since it guides us about whether it is a high or low urinary infection, through the fist-percussion and other renal palpation maneuvers, the examination of the ureteral points, palpation and percussion of the bladder, digital rectal examination in prostatitis; like the rest of the abdominal examination that rules out any other process that can be interpreted as a non-urinary origin.

Complementary study methods are essential when a urinary tract infection is suspected, in order to complete the adequate investigation of the aforementioned infectious process, not only to know the causative agent, but to rule out anatomical or functional problems capable of hindering the favorable evolution of a certain process.

Perform in every patient before starting a therapeutic scheme, an adequate collection of urine sample capable of isolating the germ. A comprehensive ultrasound study of the urinary system is necessary in every patient with suspected infection in any part of the urinary system, as it is a simple, safe, inexpensive method with a high diagnostic yield. When the picture indicates so, radiological studies such as direct renovesical X-ray and / or an excretion program with post-voiding plaque or possibly a CT of the abdomen and pelvis should be carried out, all this if they are not allergic to penicillins. Or a magnetic nuclear uro-resonance, if you are allergic to iodine or because of a special diagnosis.

A voiding cystourethrogram if urethral reflux or stricture is suspected. An actual scan should be used for evaluation of individual kidney function.

Forms of presentation

Acute cystitis in women : They are a frequent reason for consultation. Approximately 25 to 35% of women between the ages of 20 and 40 have had an episode of UI in their lifetime. Most occur in women with a normal functional and urinary tract. During the first year of life, women and men have a similar risk of developing UI. The difference between both sexes increases especially between 16 and 35 years, when the risk is 40 times higher in women. After age 60, the risk is balanced for both sexes, due to prostatic hyperplasia.

Dysuria and / or frequency without fever in sexually active women is the most common form; the clinical examination is not usually positive.

Predisposing factors:

  • Frequent sexual intercourse
  • Previous UI
  • Absence of urination after sexual intercourse
  • Use of diaphragm and spermicides for changes in vaginal flora

The presence of vaginal symptoms (discharge, burning, itching, etc.) reduces the possibility of urinary infection. Low back pain, new-onset urinary incontinence, suprapubic pain, and a history of prior UI increase the possibility. Installation is usually abrupt <3 days.

In the presence of “classic” urinary symptoms, the possibility of UI is greater than 80% and exceeds the predictive value of the test strips and urine sediment.

For this reason, given an adequate anamnesis and the presence of a classic picture, antibiotic treatment could be started without carrying out a sediment study.

Dysuria may also correspond to Chlamydia trachomatis infection or less frequently Gonococco. When the patient has had a new sexual partner in recent weeks with urethral symptoms and a history of sexually transmitted infection, the diagnosis of urethritis is more likely.

Although cystitis are not serious infections, they generate significant morbidity. Forman et al. found that each episode of UI causes an average of 2.4 days of absence from work and 0.4 days of bed rest.

It is mandatory to study the patient with a urine culture and an ultrasound, in order to rule out lithiasis, anatomical and functional abnormalities; and determine the causal agent.

Pyelonephritis in women: It generally occurs in women between 18 and 40 years of age, and is considered uncomplicated when there is no obstruction to urinary flow or that may lead to therapeutic failure. It can manifest clinically with a picture that ranges from mild with mild low back pain and dysuria to a picture of sepsis due to gram negative bacilli. Characteristics of this condition are fever with or without chills, lumbar pain and costovertebral angle pain, abdominal pain, nausea, and vomiting. 80% have a bacterial count greater than 100,000 cfu / ml. In more than 95% of cases a single microorganism is found.

Diagnosis is based on a mid-stream urine culture sample, ultrasound, routine laboratory, and in some cases requires serial blood cultures (in 97.6% the results are consistent with urine cultures) and tomography.

Urinary infection in pregnant women: It has an incidence of 8%, being one of the most frequent complications during pregnancy. The greatest risk begins during the 6th gestational week and peaks between the 22nd to the 24th week. 90% develop ureteral dilation, physiological hydronephrosis of pregnancy, which, together with increased voiding volume and decreased bladder and ureter tone, predisposes to greater urinary stasis and increased vesicoureteral reflux. About 70% have glycosuria and proteinuria contributing to an increased risk of UI.

UTIs not treated during pregnancy are associated with higher fetal mortality, prematurity, and low weight.

The most common microorganism is E Coli, followed by Klebsiella, Enterobacter, and Protheus mirabilis. Less frequently, gram-positive cocci such as Staphylococcus saprophiticus and Streptococcus agalactiae are isolated.

Forms of clinical manifestations:

  • Asymptomatic bacteriuria
  • Cystitis
  • Pyelonephritis

Urinary tract infections in postmenopausal women: the incidence varies between 10 and 30% in women. In this population there is greater vaginal colonization with gram-negative bacilli and a higher incidence of bacteriuria, which are correlated with the changes that the vaginal environment undergoes when previously preponderant bacilli disappear, the increase in pH, and in some patients, urinary incontinence. cystocele, post-voiding residue and belonging to the non-secreting ABO group, increases predisposition significantly.

Urinary infections in elderly women or residents of geriatric institutions: They constitute between 20 and 30% of all infections. In these types of institutions, between 4 and 7 ATB courses are prescribed per 1000 residents per day for all indications. It is estimated that between 25 and 75% of these prescriptions are inappropriate. As risk factors, catheterizations, urinary incontinence, exposure to antibiotics and functional alterations can be mentioned.

Infections in patients with stones: Stones may be present in patients with recurrent UTI. Bacteria colonize the interstices, and manipulation during lithotripsy or persistent obstruction can lead to severe infections. UTIs caused by urease-producing organisms (Proteus, Staphylococcus aureus, Klebsialla, Providencia, Pseudominas, Ureaplasma urealyticum, Corynebecterium urealyticum, etc.) are inducers of struvite stone formation. These stones are fast growing.

Urinary Infection in Men: In young men up to 50 years of age, it is rare and is always considered complicated, constituting 5 infections per 10,000 people per year. From that age there is an increase secondary to prostate enlargement, prostatitis, instrumentation of the urinary tract, etc.

Although cystitis and pyelonephritis are common diagnoses in both sexes, various forms of UI are associated with risk factors exclusive to men, such as urinary obstruction of prostate origin, or cystourological procedures frequently used in the evaluation of urinary symptoms.

Sexual history must be taken into account since the bacteria producing UI in men are correlated with those found in vaginal flora. Anal intercourse increases the risk of UI, as does the practice of inserting objects into the urethra. Uncircumcised patients are at higher risk for UI. Also increases the frequency of UI, the presence of HIV.

Significant bacteriuria is considered to be the presence of> 30,000 CFU / ml of a single and predominant flora. Like women, gram-negative bacteria such as E coli predominate, responsible for between 40 and 50% of the episodes. Also Proteus, providencia, enterococcus, staphylococus, etc.

Urinary infection in diabetic patient: Regardless of other factors, diabetes triples the risk of asymptomatic bacteriuria and UI, regardless of the clinical form of diabetes. UI should be considered complicated in itself in this type of patient. The development of the clinical picture in women is preceded by the colonization of the vaginal epithelium and the perineum by the causative agent (gram negative bacilli). From there they ascend to the bladder. Patients with acute pyelonephritis have a worse prognosis. Diabetes is associated with more severe forms of clinical presentation of UI such as xanthogranulomatous pyelonephritis and renal and perirenal abscesses. Pyelonephritis and emphysematous cystitis is a necrotizing infection that involves the renal parenchyma and perirenal tissue. More than 90% occur in diabetics.

Urinary infection in catheterized patient: It is usually the most frequent cause of nosocomial infection (40%) and in 80% they are related to the placement of catheters for bladder drainage. They are difficult to prevent. The incidence of bacteriuria varies between 3% and 10% per day. Of the patients with bacteriuria, 10-20% have symptoms developing a UI, and between 1 and 4% develop bacteriuria.

The presence of significant bacteriuria, accompanied by pyuria and symptoms, should be considered as a UI.

They are divided into two subtypes: Patients with a short catheterization duration (less than 30 days) have a prevalence of bacteriuria of 15% and a duration of catheterization averaging 2 to 4 days. The most frequent isolated germs are: E coli, Klebsiella pneumoniae, P miravilis, Pseudomonas aeruginosa, staphylococcus a, and epidermidis, enterococcus and candida.

Patients with long-term catheterization (more than 30 days) in patients with chronic diseases. The prevalence of bacteriuria is 90 to 100% and the duration of probing varies from months to years. The isolated germs are similar, but add Providencia Stuartii, Morganella Morgagni, Enterococcus and Candida. Polymicrobial infections are common.