Urinary tract infection (UTI) is the infection of urinary tract. Anatomically, it can be divided into upper and lower urinary tract infection. Most common symptoms are fever, chills and rigor, foul smelling urine and other constitutional symptoms. Different risk factors include vesico-ureteric reflux, neurogenic bladder, calculi in urinary tract, strictures etc. Culture and sensitivity test is the gold standard for diagnosis of UTI. Antibiotics are the treatment of choice depending on the causative organisms, drug resistance, pharmacokinetic of the drug etc.


Image: “Bacteriuria pyuria 4” by Steven Fruitsmaak License: CC BY-SA 3.0

Definition of Urinary Tract Infection

The occurrence of UTI is quite common. It is defined as a condition in which bacteria invades, persist, and multiply within the urinary tract. Most commonly it is caused by gram negative organisms.

Epidemiology of Urinary Tract Infection

  • Incidence of UTI is 0.5–0.7 episodes per person per year.
  • Females are most commonly affected.
  • Recurrence is also more common in female patient (25 %).
  • The host defence factor plays an important role in preventing urinary tract infections.

Urinary tract infections (UTI) can be anatomically subdivided into lower tract infection (including urethritis, prostatitis and cystitis) and upper tract infections (pyelonephritis and perinephric abscess).

UTI is associated with multiplication of micro-organisms in the urinary tract by the presence of more than 105 organisms per ml of midstream sample of urine. This is defined as “significant bacteriuria”.

According to clinical pictures it can be classified as

  1. Asymptomatic bacteriuria: it is the presence of bacteriuria, i.e., more than 105 organisms per ml on two occasions in women and one occasion in men. It indicates UTI without the symptoms. It is commonly seen during pregnancy.

  2. Symptomatic bacteriuria: it includes acute urethritis, acute cystitis, acute prostatitis, acute pyelonephritis and septicaemia with septic shock

Etiology of Urinary Tract Infection

  • More than 80 % of UTI is due to bacteria Escherichia Coli.
  • Other bacteria involved in UTI are Proteus, Klebsiella, Enterobacter, Pseudomonas, Serratia, chlamydia trachomatis, and Neisseria gonorrhoea.
  • More than one third of females with dysuria and frequency have either insignificant bacteriuria in the mid-stream urine sample or completely sterile culture. This subset of patients has been defined as having acute urethral syndrome. This infection is due to either usual organism described above but their number are less than 105 micro-organisms per ml of urine. But some time non-specific organism like chlamydia trachomatis, and Neisseria gonorrhoea may be found.

Risk factors associated with UTI

The following are the host factors aggravating the UTI or helps in accentuating the symptoms of UTI

Anatomical factors

  • Posterior urethral valve
  • Vesico-ureteric reflux
  • Urethral stricture
  • Benign prostatic hypertrophy

Functional factors like neurogenic bladder

Familial susceptibility

Disease conditions

  • Diabetes
  • Immunosuppression
  • Calculi
  • Congenital abnormality
  • Foreign bodies like stent or catheter

Factors associated with females

  • Voiding habits
  • Post-menopausal state
  • Perineal hygiene
  • Spermicidal jelly use
  • Vaginal douching

Factors associated with males

  • Phimosis
  • Chronic prostatitis
  • Seminal vesiculitis
  • Epididymorchitis

Causes of sterile pyuria

  • Partially treated UTI
  • Bladder tumors
  • Chemical cystitis
  • Interstitial nephritis
  • Appendicitis
  • Urinary tuberculosis
  • Infection of other organisms like chlamydia or Corynebacterium

Pathogenesis of Urinary Tract Infection

Bacteria gain access to the bladder via urethra in the vast majority of cases. Bacteria then rise from the bladder to other areas to form parenchymal infection

Females are more prone to development of UTI. The reasons are a shorter urethra compared to male counterparts, gram negative bacteria residing near the anal region may colonise in the periurethral region, absence of bactericidal prostatic secretion and sexual intercourse facilitates entry of intercoital bacteria into the bladder.

Epithelium of urethra of female patients has more surface area so more organisms can attache to the surface.

Whether bladder infection ensures depends on certain factors like flushing and dilutional effect of micturition and voiding, direct antibacterial property of urine and bladder mucosa, size of inoculum, and bacterial virulence factor.

Pregnancy is associated with increased risk of UTI. During pregnancy, ureteral tone is decreased because of progesterone effect, ureteral peristalsis is decreased, and there is a transient incompetence of the vesicoureteral valves. All these factor favors the development of UTI.

Any impediments to the flow of urine as with tumours, strictures, calculi, prostatic hypertrophy in male, posterior urethral valve may favor the development of UTI.

Vesico-ureteric reflux is the condition defined as the reflux of urine from the bladder cavity up into the ureter. It occurs during the voiding or with elevated bladder pressure. As a fluid connection exists between the bladder and kidney, there is retrograde bacterial spread resulting in acute pyelonephritis. Vesico-ureteric reflux can be confirmed radiographically when retrograde movement of radio-opaque material can be demonstrated. The procedure is called micturating cystourethrography or MCU.

Instrumentation of urinary tract like catheterisation, urethral dilatation and cystoscopy can increase the chance of urinary tract infection.

Impaired defence mechanism of the body like in immunosuppression, diabetes etc. can increase the risk of UTI.

Neurogenic bladder which is the dysfunction of nervous system that regulates bladder function can increase the risk of UTI. This condition occurs in tabes dorsalis, spinal cord injury and multiple sclerosis.

Clinical Features of Urinary Tract Infection

The common symptoms of UTI are

  1. Fever with chills and rigor
  2. Increased frequency of micturition
  3. Dysuria
  4. Urgency
  5. Haematuria
  6. Suprapubic pain resulting from cystitis
  7. Strangury resulting from cystitis. After the bladder, has been emptied there may be an intense desire to pass more urine due to detrusor spasm.
  8. Urine is cloudy
  9. Foul smelling urine

Clinical features depend on the site of infection of the urinary tract. For example, symptoms pertaining to voiding are more common in lower urinary tract while pain and constitutional symptoms are more common in upper urinary tract. The following are the description of infection according to site.

Cystitis and Urethritis

Cystitis or urethritis patients may be asymptomatic or may present with urgency, dysuria, frequency, nocturia, incontinence, pain in the supra-pubic region etc. Offensive smell of the urine may be a major sign. 30 % of cases present with haematuria. Negative culture in patients presenting with dysuria, pyuria may be due to infection with chlamydia or Neisseria or herpes simplex infection. The condition called “interstitial cystitis” is of unknown etiology with symptoms like bacterial cystitis but negative urine culture. The diagnosis is confirmed by biopsy and cystoscopy.

Prostatitis and seminal Vesiculitis

These conditions mainly present with dysuria, perineal pain, frequency, voiding difficulties and painful ejaculations. Fever with chill and rigor and other constitutional symptoms are major presenting symptoms in acute bacterial prostatitis. In these cases, per-rectal digital examination should be avoided due to chance of blood stream infections. Chronic bacterial prostatitis may be asymptomatic. These conditions are important causes of recurrent UTI in male patients. Culture result of expressed prostatic secretion may confirm the diagnosis in this case.


It is the infection of renal parenchyma. Myalgia, nausea, vomiting, pain in the loin region, fever with chills and rigor are the presenting features in acute pyelonephritis. Renal angle tenderness during physical examination is a prominent finding. Significant leucocytosis with leukocyte casts may be found in the urine. Micro- or macroscopic haematuria may be found. Blood culture may be positive in a quarter of a patients. Fulminant emphysematous pyelonephritis can be seen as an acute condition in diabetic patients. In this condition, there is accumulation of fermentative gases in collecting tubles, kidney and parenchyma.

Chronic pyelonephritis is difficult to diagnose. It is mostly diagnosed by clubbed calyces with focal and diffuse renal scarring on radiograph. This usually develops in patients with vesico-ureteric reflux in early childhood.

Renal Abscess

Staphylococcus aureus is the most common bacteria causing renal abscess. It is mostly due to spread of infection from another site through blood stream. Since it is a systemic infection in majority of cases, fever, constitutional symptoms, loin pain are the presenting symptoms. Renal cortex show hypoechoic lesions on radiograph. The symptoms resemble acute pyelonephritis. Diagnosis is confirmed by aspiration and culture from the suspected area under ultrasound guidance.

A perinephric abscess is the abscess formation in peri-nephric space. It is insidious in origin as compared to renal abscess, so it remains undiagnosed for a long period of time. Flank or abdominal mass may be initial presentation.

Investigations of Urinary Tract Infection

  • Dip stick tests are often used to detect nitrite which is a metabolic product of typical pathogens of urinary tract.
  • Leucocyte esterase which is marker of inflammation can be found in dip stick test. Presence of nitrite and leucocyte esterase increases the possibilities of UTIs.
  • Clean catch technique is used to collect the clean freshly voided midstream specimen of urine. It should be examined for leukocytes, leukocyte casts, red cells etc. If these cells are found it increases the suspicion of UTI.
  • Suprapubic aspiration of urine from bladder can be used to collect uncontaminated urine sample. But now it is rarely required.
  • Gram staining and bacterial colony count can be done to identify the causative organism.
  • Culture and sensitivity testing can confirm the diagnosis.
  • Prostatic massage followed by urine culture is done if prostatitis is suspected.
  • Bladder lesion can be diagnosed by cystoscopy.
  • Obstruction, stricture, cysts and calculi can be diagnosed by ultrasonography.
  • Intravenous urography (IVU) with post void film of bladder can be a diagnostic modality for physiological and anatomical abnormalities of urinary tract.
  • Micturating cysto-urethrography (MCU) is useful in diagnosing vesicoureteric reflux and disturbed bladder emptying.
  • Pyelonephritis can be diagnosed by DMSA scan.
  • Rectal examination can be done in prostatitis but with antibiotic cover.
  • In female, with recurrent UTI, pelvic examination is mandatory to exclude cystocele, rectocele and uterovaginal prolapse.

Treatment of Urinary Tract Infection

Antibiotics are the treatment of choice in case of UTI. Choice of antibiotic depends on the culture sensitivity testing, pharmacokinetics of the drug, pH of urine etc. Uncomplicated and symptomatic UTI can be treated with a 3–5 day course of antibiotics. Clotrimazole or fluoroquinolones are treatment of choice in these cases.

Such short course treatment also eradicates the vaginal colonisation. Azithromycine or doxycycline is used in case of acute urethritis due to chlamydia infection. If a patient presents with uncomplicated UTI with upper gastrointestinal symptoms, then a single dose of parenteral antibiotics on the first day followed by oral antibiotic is preferred (single dose of 2 gm ceftriaxone or 80 mg of gentamycine or 750 mg of amikacin can be given in this case).

Prostatitis is usually treated with a 6-week course of antibiotics like quinolones and cotrimoxazole. Macrolide antibiotics or doxycycline is the second line of drug in case of prostatitis. Sometimes 12-week course is needed for prostatitis.

Antibiotic treatment is not necessary in asymptomatic individuals with catheter, stones or obstruction even if urine culture is positive. Recurrence of UTI can be either due to relapse or re-infection can be due to associated risk factors. Further investigation is required to elicit the risk factor and corrective measure can be taken. In sexually active women antibiotic prophylaxis with a single dose of cotrimoxazole can be tried. The following table shows the specific antibiotic use in certain conditions.


Common pathogens

Associated condition

Treatment schedule


Uncomplicated acute cystitis in women E coli, Staphylococcus aureus, Proteus mirabilis, Klebsiella pneumoniae Nil Trimethoprime plus sulphamethoxazole or flouroquinolones 3 days
Uncomplicated acute pyelonephritis in women E coli, Klebsiella pneumoniae, Staphylococcus Nil Amoxycillin, nitrofurantoin, cephalosporin 7 days
Complicated acute cystitis in women E coli, Staphylococcus aureus, Proteus mirabilis, Klebsiella pneumoniae Diabetes mellietus, Symptoms more than 7 days, recuurent form of UTI Trimethoprime plus sulphamethoxazole or flouroquinolones 7 days
Complicated acute cystitis in pregnant women E coli, Staphylococcus aureus, Proteus mirabilis, Klebsiella pneumoniae Pregnancy Amoxycillin, nitrofurantoin, cephalosporin 7 days

Complicated UTI

E coli, Proteus mirabilis, Pseudomonas Amoxycillin, nitrofurantoin, cephalosporin 14 days

Complicated UTI

E coli, Proteus mirabilis, Pseudomonas Severe infection in pregnancy Amoxycillin, nitrofurantoin, cephalosporin 14 days

Acute urethral syndrome

Urea plasma urealyticum, Mycoplasmhominis Sexual activity, dysuria, pyuria, Non-gonococcal urethritis Doxycycline 5 days
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