Urinary Tract Infection



  • Outpatient UTI Accounts for 7 Million Office Visits Per Year in US

Sex and Age-Related Factors Associated with Urinary Tract Infection

  • Female UTI
    • Incidence of UTI Increases Markedly After Onset of Sexual Actvity in Adolescence
    • Incidence of Symptomatic UTI in Sexually Active Females (In a University Population): 0.5-0.7 cases per person-year
      • Risk Factors
        • Sexual Intercourse
        • Recent Spermicide Use
        • History of UTI
    • Incidence of Cystitis in Post-Menopausal Female: 0.07 cases per person-year
    • Incidence of Pyelonephritis: 12-13 cases per 10k females per year (lower incidence than that for cystitis)
  • Male UTI
    • Incidence: 5-8 UTI per 10k young adult males per year
    • Most Male UTI’s Occur in Infants and Elderly (Usually Associated with Urologic Abnormalities or Instrumentation)
      • However, UTI May Occur in Males age 15-50 y/o (with Risk Factors Being Anal Insertive Intercourse and Lack of Circumcision)
  • Factors Related to Lower Incidence of Symptomatic Bacteruria/Symptomatic UTI in Males than Females
    • Longer Urethral Length
    • Drier Peri-Urethral Environment: with less frequent peri-urethral colonization
    • Antibacterial Substances Contained in Prostatic Fluid

Factors Suggesting “Complicated” Urinary Tract Infection

  • Demographic Features
    • Advanced Age
    • Male Sex
    • Pregnancy (see Pregnancy)
  • Comorbid Conditions
  • Infection-Related Characteristics
    • Hospital-Acquired Urinary Tract Infection
    • Recent Antibiotic Use
    • Recent Urinary Tract Instrumentation
    • Resistant Urinary Pathogen
    • Symptoms For At Least 7 Days Before Seeking Medical Attention
  • Urinary Tract Functional/Anatomic Abnormalities



Route/Mechanism of Urinary Tract Infection

  • Ascending Infection: in female, colonization of vaginal introitus with pathogens from fecal flora -> ascension via urethra into bladder (and ultimately to kidneys, via ureters)
  • Bacteremic Seeding of Kidney: causes some cases of pyelonephritis
  • Seeding of Kidneys from Bacteria Within Lymphatics: may play a role in some cases of pyelonephritis


Urinalysis (see Urinalysis)

  • General Comments
    • Dipstick positivity for leukocyte esterase or nitrite has 75% sensitivity/82% specificity for detection of UTI: test is not helpful to rule out UTI if symptoms are consistent with UTI and dipstick is negative for both (due to low sensitivity)
  • Nitrite
    • Assay: dietary nitrate (normally present in the urine) is converted to nitrite by the nitrate reductase enzyme in certain Gram-negative bacteria -> results in pink color change on dipstick
      • Specific Gram-negative bacteria (E Coli, Citrobacter, Klebsiella, Proteus, Serratia) possess nitrate reductase and are capable of this conversion
        • Pseudomonas and Gram-positive bacteria (Enterococcus, etc) do not possess the nitrate reductase enzyme
      • False-Positive: use of phenazopyridine, beet ingestion
    • Interpretation: positive nitrite indicates presence of the specific Gram-negative bacteria noted above
  • Leukocyte Esterase
    • Assay: granulocyte leukocyte esterase catalyzes the hydrolysis of an amino acid ester to liberate 3-hydroxy-5-phenyl pyrrole! which reacts with a diazonium salt -> results in purple color change on dipstick
      • Sensitivity: 75-96%/Specificity: 94-98% for >10 WBC per hpf
    • Interpretation: positive nitrite indicates presence of pyuria
  • Protein: xxx
  • Ketone: may be mildly positive in cases with associated dehydration and starvation ketoacidosis or with concomitant diabetic ketoacidosis
  • RBC (on Microscopy): elevated RBC (microscopic or gross hematuria) may be seen
    • Hematuria is Common in UTI, But Not in Urethritis or Vaginitis
  • WBC (on Microscopy): >10 WBC/uL (pyuria) indicates UTI (cystitis or pyelonephritis)
    • Pyuria May Be Absent in Some Cases of Pyelonephritis with Urinary Tract Obstruction
  • Casts
    • WBC Casts: indicate pyelonephritis

Urine Gram Stain (see Urine Culture)

  • Assay: performed on spun urine
  • Interpretation: should be positive if there are >100k colonies in culture (which is performed on unspun urine)

Urine Culture (see Urine Culture)

  • Assay: clean-catch (in female: after cleansing of external urethra prior to collection) or via Foley catheter
  • Interpretation: historically considered positive if there are >100k CFU/mL in culture (this originated from literature in pregnant females with first void morning urine samples)
    • However, urinary tract infection may occur with colony counts <100k CFU/mL
      • Male: colony count >10k CFU/mL is considered positive
    • Lower colony counts of coliforms (E Coli, etc) are likely to represent significant bacteriuria
    • In some female cases with infection due to Chlamydia Trachomatis/Neisseria Gonorrhoeae/HSV, culture may be negative
  • Isolation of Other Organisms: lactobacillus, Enterococcus, Staphylococcus Epidermidis and group B Streptococcus isolated from a voided urine culture in female may suggest contamination
    • However, presence of organism in midstream voided urine at high colony count and with pure growth may suggest that organism is etiologic

Abdominal/Pelvic Computed Tomography (CT) (see Abdominal-Pelvic Computed Tomography)

  • Diagnostic of nephrolithiasis and hydronephrosis
  • May demonstrate emphysematous pyelonephritis or emphysematous cystitis

KUB (see Kidneys-Ureters-Bladder X-Ray)

  • May occasionally detect nephrolithiasis

Renal Ultrasound (see Renal Ultrasound)

  • May be required to rule out hydronephrosis (due to obstruction), anatomic abnormailities, nephrolithiasis, etc

Clinical Presentations

Asymptomatic Bacteriuria

  • Definition: positive urine culture in the absence of symptoms
    • Male: defined as single clean-catch voided urine with single bacterial species isolated in count >100k CFU/mL in absence of symptoms
    • Female: xxxx
  • Epidemiology
    • Prevalence of Male Asymptomatic Bacteriuria
      • Young Male: rare
      • Elderly Male: prevalence of 6%
    • Prevalence of Female Asymptomatic Bacteriuria
      • Young Female: xxx
      • Elderly Female: prevalence of 18%
  • Indications to Preoperatively Screen for Asymptomatic Bacteriuria: other than urologic procedures, the risk of surgical site infection for other surgical procedures (including procedures with high risk of infection, like joint arthroplasty) with pre-operative asymptomatic bacteriuria probably does not warrant screening
    • Pre-Trans-Urethral Resection of Prostate (TURP): due to risk of bacteremia/sepsis
    • Pre-Urologic Procedures Where Mucosal Bleeding is Anticipated: due to risk of bacteremia/sepsis

Asymptomatic Candiduria (see Candida)

  • xxx

Acute Cystitis

  • Definition: infection of urinary bladder (lower urinary tract)
    • May occur alone or in conjunction with pyelonephritis or prostatitis
  • General Comments
    • Males with Recurrent Cystitis: should undergo evaluation for prostatitis
  • Cloudy Urine
  • Dysuria (see Dysuria)
  • Gross Hematuria (see Hematuria)
  • Suprapubic or Low Abdominal Pain (see Abdominal Pain)
  • Urinary Frequency
  • Urinary Urgency

Emphysematous Cystitis

  • Epidemiology: rare
  • Risk Factors
    • Diabetes Mellitus (see Diabetes Mellitus)
    • Female Sex
    • Immunocompromised State
    • Neurogenic Bladder
    • Prior Urinary Tract Infection
    • Renal Transplant (see Renal Transplant)
    • Urinary Stasis
  • Specific Microbial Etiologies
  • Mechanism: gas may appear in the wall of the bladder by either transluminal dissection of gas or true infection of the bladder wall with pathogens
  • Diagnosis: abdominal/pelvic CT scan
  • Clinical Manifestations
    • Abdominal Pain (see Abdominal Pain)
    • Gas In Bladder Wall (Seen on CT Scan): due to bacterial or fungal fermentation
    • Pneumaturia (see Pneumaturia): highly suggestive (although not usually noted by the patient)
  • Prognosis: delayed diagnosis and treatment may result in overwhelming infection, extension to ureters and renal parenchyma, bladder rupture, and death

Acute Pyelonephritis

  • Definition: infection of kidney (upper urinary tract)
    • May occur alone or in conjunction with cystitis
  • General Comments
    • Symptoms may co-exist with those of acute cystitis
  • Abdominal Pain (see Abdominal Pain)
  • Costovertebral Angle Tenderness
  • Fever/Chills (see Fever)
  • Flank Pain (see Flank Pain): present in cases with pyelonephritis
  • Diarrhea (see Diarrhea)
  • Nausea and Vomiting (see Nausea and Vomiting)

Emphysematous Pyelonephritis

  • Risk Factors
  • Staging (Huang and Tseng, 2000)
    • Class 1: gas confined to the collecting system
    • Class 2: gas confined to the renal parenchyma alone
    • Class 3A: perinephric extension of gas or abscess
    • Class 3B: extension of gas beyond the Gerota fascia
    • Class 4: bilateral emphysematous pyelonephritis or pyelonephritis in a solitary kidney
  • Diagnosis : abdominal/pelvic CT scan
  • Clinical Manifestations
  • Prognosis: may be fatal, if not rapidly treated



Measures Which Do Not Have Demonstrated Clinical Efficacy

  • Chlorhexidine Gluconate Skin Decontamination (see Chlorhexidine Gluconate)
    • Clinical Efficacy
      • Randomized Trial of Daily Chlorhexidine Bathing to Prevent Healthcare-Associated Infections ( JAMA, 2015) [MEDLINE]
        • Daily Chlorhexidine Gluconate Bathing Did Not Decrease the Incidence of Healthcare-Associated Infections (Central Line-Associated Bloodstream Infections, Catheter-Related Urinary Tract Infection, Ventilator-Associated Pneumonia, or Clostridium Difficile)


Acute Cystitis

Oral (PO) Antibiotics

Intravenous (IV) Antibiotics (usually not required for acute cystitis, unless concomitant acute pyelonephritis is present)

Clinical Guidelines for Short-Course Antibiotics in Common Infections (Annals of Internal Medicine, 2021) [MEDLINE]

Emphysematous Cystitis

Acute Pyelonephritis

Oral (PO) Antibiotics

Intravenous (IV) Antibiotics

Emphysematous Pylelonephritis

Treatment Duration

Urinary Tract Analgesic

Treatment of Pre-Operative Asymptomatic Bacteriuria

Treatment of Pre-Operative Symptomatic Urinary Tract Infection

Management of Staphylococcus Aureus Bacteriuria

Management of Candiduria