Urinary tract infections (UTIs) are infections of the urinary tract system (bladder, urethra, kidneys) that are generally caused by bacteria, especially E. coli. Women are at high risk of contracting UTIs due to a shorter urethra and the proximity of the anal and genital regions. Other risk factors include sexual intercourse, indwelling urinary catheters, pregnancy, and abnormalities of the urinary tract. Clinical findings depend on which part of the urinary tract is affected. Lower UTIs manifest with dysuria, suprapubic pain, urinary urgency, and increased urinary frequency, whereas upper UTIs additionally manifest with fever and flank pain. Diagnosis is usually clinical and can be supported with findings of pyuria, bacteriuria, and positive leukocyte esterase and nitrites on urinalysis. Further evaluation with urine culture and/or imaging may be required for patients with complicated cystitis. Treatment likewise depends on which part of the urinary tract is affected. First-line empiric antibiotic therapy for uncomplicated UTIs includes outpatient therapy with oral trimethoprim-sulfamethoxazole, nitrofurantoin, or fosfomycin for up to 7 days. For complicated UTIs antibiotic therapy should be extended for 7–14 days. Pregnant women with cystitis should be screened and treated if positive for asymptomatic bacteriuria.
- Infection ascends from the urethra to the bladder
- Can ascend further to the ureters and the renal pelvises (see “ ”)
- Causative organisms
- : leading cause of UTI (approx. 80%) 
- Staphylococcus saprophyticus: 2nd leading cause of UTI in sexually active women
- Klebsiella pneumoniae: 3rd leading cause of UTI
- Proteus mirabilis
- Nosocomial bacteria: Serratia marcescens, Enterococci spp., and Pseudomonas aeruginosa are associated with increased drug resistance.
- Enterobacter species
- Ureaplasma urealyticum
- Immunocompromised patients and children are particularly susceptible to viral UTIs. 
- Adenovirus, cytomegalovirus, and BK virus are commonly involved in hemorrhagic cystitis. 
- Yeast: rare (usually Candida species)
- Abacterial: interstitial cystitis (see “Differential diagnosis” below)
- Structural or functional abnormalities of the urinary tract 
- Pregnancy: hormonal changes during pregnancy → urinary stasis and vesicoureteral reflux → increased risk of UTIs
- Postmenopause: ↓ estrogen → ↓ vaginal lactobacilli → ↑ vaginal pH → ↑ colonization by E. coli 
- Chronic constipation: common cause of UTIs in children
- Prior conditions
- Honeymoon cystitis; : a type of lower UTI that occurs in women after having sexual intercourse for the first time or after a prolonged period of abstinence.
- Diaphragm and spermicide use
Catheter-associated urinary tract infection (CAUTI)
- Caused by indwelling urinary catheters
- Most common cause of
According to anatomic location 
- Upper UTI: : upper urinary tract comprises kidneys and the ureters (pyelonephritis)
- Lower UTI: lower urinary tract comprises the bladder (cystitis, the most common location of UTI), urethra ( ), and prostate in males ( )
According to predisposing factors 
- Uncomplicated UTI: UTI in immunocompetent, premenopausal, nonpregnant women without conditions predisposing them to infection or therapy failure
Complicated UTI: UTIs in men, pregnant or postmenopausal women, children, and individuals with factors predisposing them to infection or therapy failure. Such factors include:
- Presence of any significant functional or anatomical abnormalities (e.g., BPH, obstruction, stricture)
- UTI that spreads beyond the bladder (e.g., sepsis, prostatitis)
- History of urological pathologies (e.g., neurogenic bladder, kidney cysts, stones)
- History of impaired renal function or renal transplantation
- Diabetes mellitus or other metabolic disorders
- Immunocompromise (e.g., transplant recipients, HIV/AIDS)
- Recent history of instrumentation (e.g., cystoscopy) or placement of medical devices (e.g., urinary catheter, nephrostomy tubes, stents)
- Infection with a resistant uropathogen or recent antibiotic use
- History of UTIs in childhood or at least one episode of pyelonephritis in the last year
According to source of infection
- Community-acquired: UTI acquired outside of the hospital setting that manifests within 48 hours of hospital admission. 
Healthcare-associated (nosocomial) UTI
- Most common nosocomial infection 
- Most commonly caused by indwelling urinary catheters (see in “Etiology”)
- Recurrent UTI: ≥ 3 infections in one year or ≥ 2 infections in 6 months
- Lower urinary tract infection 
- Upper urinary tract infection 
- Additional features (special patient groups) 
- Symptomatic, uncomplicated UTIs can be diagnosed clinically.
- The most important initial diagnostic test for UTI is urinalysis (can be performed by using a urine dipstick test or microscopy ).
- Presence of any organisms in bacterial culture confirms the diagnosis.
- Imaging can be performed to rule out less common causes (e.g., urinary tract obstruction) or complications (e.g., pyelonephritis) of UTI.
Laboratory tests 
- Best initial test
- Individuals with predisposing factors have an increased risk of infection or therapy failure (see “ ” in “Classification”).
Urinalysis collection method
- Clean-catch midstream sample: necessary to avoid contamination with vaginal or skin flora
- Straight catheterization of the bladder or suprapubic aspiration: performed if a clean catch cannot be obtained without contamination (e.g., in children who are not toilet trained)
- Urethral catheterization is contraindicated due to increased risk of bacteremia.
- Diagnostic criteria for UTI
Findings indicative of UTI 
- Positive leukocyte esterase; : an enzyme produced by WBC that indicates pyuria
- Positive nitrites: indicates presence of bacteria that convert nitrates to nitrites, which are most commonly (e.g., E.coli)
- Positive urease: indicates presence of (e.g., Proteus, Klebsiella, S. saprophyticus), which cause the urine to become more alkaline (pH > 7)
- Other findings
- Diagnostic criteria for UTI
- Typical colony findings
- Other pathogens
- CT scan without contrast 
Interstitial cystitis (painful bladder syndrome) 
- Description: chronic, noninfectious cystitis of unknown etiology associated with recurring suprapubic pain
- Uncommon condition (0.6– 2% of women in the US) 
- Sex: ♀ > ♂
- Peak age: ≥ 40 years
- Associated with history of previous UTIs and/or diagnosis of other pain syndromes (e.g., fibromyalgia, irritable bowel syndrome)
- Individuals diagnosed with this condition are more likely to suffer from depression and anxiety disorders. 
- Symptoms have a gradual onset and last ≥ 6 weeks (required for diagnosis).
- Pain relieved by voiding and worsened by bladder filling (most common feature)
- Suprapubic pain, pressure, or discomfort 
- Increased urinary urgency and frequency
- Other exacerbating factors: sexual intercourse, exercise, alcohol use, and prolonged sitting
Diagnosis: Interstitial cystitis is generally a clinical diagnosis.
- Medical history to rule out other diagnoses
- Physical examination: anterior vaginal wall and bladder base tenderness on bimanual pelvic exam
- Urinalysis with microscopy and urine culture to rule out bacterial cystitis
- Other tests: indicated only in individuals with complex presentation 
Behavioral modification (first-line): indicated for all diagnosed individuals 
- Avoidance of triggers (e.g., stress, alcohol, coffee)
- Fluid intake management based on symptoms
- Bladder training
- Stress management practices
- Multimodal pain management
- Invasive procedures: used as a last resort
- Behavioral modification (first-line): indicated for all diagnosed individuals 
Asymptomatic bacteriuria 
- Presence of ≥ 100,000 CFU/mL in at least two voided urine samples in patients with no symptoms of UTI; (e.g., dysuria, frequency, urgency, suprapubic pain)
- Bacteriuria typically resolves spontaneously in healthy, nonpregnant women without any side effects.
- Women with asymptomatic bacteriuria may progress to symptomatic UTI in the future; more often than women with no bacteriuria.
- Etiology: E. coli is the most common causative organism.
- Risk factors
- Diagnosis: urinalysis with microscopy
- Treatment is recommended in:
- Treatment is not recommended in:
Other differential diagnoses
- Urethritis with sexually transmitted infections (e.g., Neisseria gonorrhoeae, Chlamydia trachomatis), Candida, or irritants
- Tuberculous cystitis (see “ ”)
- Drug-induced cystitis (e.g., cyclophosphamide, NSAIDs) or radiation-induced cystitis
- Hemorrhagic cystitis
- Structural abnormalities of the urethra (e.g., diverticula, strictures)
- Other diseases of the bladder (e.g., urolithiasis, bladder cancer, foreign objects)
The differential diagnoses listed here are not exhaustive.
Antibiotic therapy for uncomplicated UTIs
Principles of therapy 
- Supportive treatment (increased fluid intake) may be sufficient, but antibiotic therapy should be recommended.
- Empiric treatment can be given for uncomplicated cystitis.
- Local resistance patterns should guide the choice of empiric therapy.
- Persistent symptoms after 48–72 hours of antibiotic therapy suggest possible complicated cystitis and/or indicate the need to change the empiric therapy.
- Phenazopyridine, a urinary analgesic, can be used for dysuria for 1–3 days.
- Urine cultures after treatment are not required if the patient's symptoms resolve. 
Treatment of acute uncomplicated lower UTIs
First-line treatment 
- Given orally as outpatient therapy 
- Fosfomycin (single dose): should be avoided in suspected pyelonephritis
- Nitrofurantoin for 5–7 days: should be avoided in patients with renal insufficiency or in suspected pyelonephritis
- Trimethoprim-sulfamethoxazole (TMP-SMX) for 3 days: should be avoided in areas with high resistance (> 20%) or in patients who have used it within the past 3 months
- Second-line treatment: should be used with caution due to increasing patterns of resistance
Treatment of uncomplicated upper UTIs
See “Treatment” section for “.”
Antibiotic therapy for complicated UTIs
Treatment is generally given for 7–14 days in complicated UTIs.
- Antibiotics of choice
- Considerations for treatment in men
Antibiotic therapy for recurrent infections 
- If the patient becomes symptomatic within 2 weeks after treatment of a UTI, the patient can be restarted on the same treatment for 2 additional weeks and a urine culture should be obtained.
- A single recurrent infection can be treated in the same way as an uncomplicated UTI.
- Chemoprophylaxis can be given to patients with recurrent UTIs.
In male individuals
- In pregnant women 
We list the most important complications. The selection is not exhaustive.
Behavioral modifications 
- Increased fluid intake
- Timely bladder voiding
- Postcoital voiding
- Adequate genital hygiene
- Intermittent straight catheterization
- Prophylaxis: indicated for recurrent urinary tract infections (see “Treatment of recurrent infections” above)
Special patient groups
UTI during pregnancy
- Pregnancy may increase the risk of recurrent bacteriuria and UTIs.
- Factors involved
Asymptomatic bacteriuria in pregnancy 
- Screening for asymptomatic bacteriuria is recommended for all pregnant women in the first trimester.
- Diagnostic criteria for asymptomatic bacteriuria on urine culture: two consecutive urine samples with the same pathogen with > 105CFU/mL or a urine sample obtained with catheterization with > 102CFU/mL
- Treatment is always required for asymptomatic bacteriuria in pregnancy (as it is more likely to lead to pyelonephritis in these patients) and should include: 
- Follow-up culture is required.
Treatment of UTIs in pregnant women 
- Lower UTI
- Empiric treatment: aminopenicillins; (e.g., amoxicillin-clavulanate), oral cephalosporins; (e.g., cefpodoxime) or fosfomycin
- Alternatives (especially during the 2nd and 3rd trimesters): TMP-SMX, nitrofurantoin
- Many antibiotics used to treat UTIs in nonpregnant patients are contraindicated during pregnancy (see “ ”).
- Upper UTI: hospitalization and administration of intravenous antibiotic (see “ ”) 
- Lower UTI
UTI in children and adolescents 
- UTIs are common in children.
- Approx. 8% of girls and 2% of boys will have had a UTI by the age of 7 years.
- Risk factors
Urinalysis and urine culture are indicated in patients with suspected UTI that fulfill one of the following criteria
- Any febrile infant or child with an abnormal urinary tract or family history of urinary tract disease
- Circumcised boys < 12 months of age with: fever or no obvious cause of infection
- Female and uncircumcised male children between 2–24 months of age with one of the following: history of previous UTI, fever of unknown source or duration > 24 hours, ill appearance, suprapubic tenderness
- Children > 24 months with a suspected UTI based on urinary symptoms (see “Clinical features” above)
- Criteria for diagnosis includes both a positive urinalysis (pyuria and/or bacteriuria) and urine culture (> 50,000 CFU/mL).
Renal and bladder ultrasound indicated in:
- Children aged 2–24 months with a febrile UTI
- Children with either treatment failure, abnormal voiding, abdominal mass, recurrent UTI, or poor likelihood of follow-up
- Voiding cystourethrography (VCUG) used in:
- Urinalysis and urine culture are indicated in patients with suspected UTI that fulfill one of the following criteria
- Treatment principles in children are similar to those in adults.
- Empiric therapy
- When associated with structural abnormalities, additional management of the underlying condition may be required.