Urinary Tract Infection
last authored: Feb 2010, David LaPierre
last reviewed:
Introduction
Urinary tract infections (UTIs) are inflammatory response to bacterial invasion of the urothelium. UTIs are thought to be the most common bacterial infections, accounting for 1.2% of female visits to a GP and 0.6% of male visits. This amounts to almost 700,000 dictor visits/year in Canada. Perhaps 50% of women will have at least 1 UTI during their lifetime.
UTIs are more common in women due to their shorter urethras, and can occur from infancy through old age. Cystitis describes infection of the bladder, while the more serious pyelonephritis represents ascending infection of the kidneys.
The urethra contains many commensal organisms, including lactobacilli, streptococci, and coagulase-negative staphylococci. By age 1 y, almost 3% of males and 1% of females have bacteuria.
The Case of...
A 34 year-old woman comes to you with two days of painful urination. She thinks she might have a UTI.
- how would you diagnose UTI?
- what treatment, if any, would you use?
Causes and Risk Factors
Uncomplicated (in young women)
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Complicated
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Complicating factors change the types of infecting organisms and faciliatate persistence within the urinary tract. Other risk factors for complicated UTIs include:
- urinary tract surgery or instrumentation (ie nephrostomy tubes)
- functional or anatomic abnormality of the urinary tract
- chronic renal disease
- kidney stones
- diabetes (UTI with renal complications)
- immunosuppression
- incontinence
- funtional or neurological impariment
- postmenopausal changes
Common Risk Factors
Children: males have a higher risk than females, likely due to the presence of foreskin.
Vesico-ureteral reflux represents retrograde flow, provides access to the kidneys and increases the risk of renal involvement and scarring. It is present in 25% of children with UTI.
Obstructions increase UTI susceptibility, due to dysfunctional voiding, neurogenic problems, anatomic blocks, or foreign bodies.
Catheter-associated UTIs account for about 40% of nosocomial infections, primarily due to indwelling catheters. Risk increases duration of catheterization. Risk in closed systems is 5-10% per day. Organisms can originate from periurethral area, from the collecting bag, or through breaks in the closed system.
Genotypic traits seem to cause some epithelial cells to be more susceptible to bacterial adhesion: HLA-A3. Components of vaginal fluid also affect adherence, potentially mediated by IgA.
Pathophysiology
Ascending routes are the most common, with fecal bacteria entering the urethra. Hematogenous or lymphatic spread is rare, though UTI can follow endocarditis, bactermia, tuberculosis, or disseminated infection.
Most UTIs are caused by single-pathogen facultative anaerobes originating for the bowel flora. E coli is by far the most common pathogen, accounting for 85% of community-acquired and 50% of nosocomial infections. Uropathogens are successful due to their ability to survive and grow in an acidic, aerobic environment, resist phagocytosis, and resist flushing of urinary tract through adherence factors.
Community-Acquiredmost common (KEEPS)
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Noscomial (acute)
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Nosocomial (chronic)
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Proteus, Morganella, Provincia are all urease-producing organisms. Increases in pH lead to crystal formation. Biofilm formation protects bacteria and allows catheter colonization.
Normal flora of the periurethral and urethral regions include lactobacilli, coagulase-negative staphylococci, corynebacteria, and streptococci.
Bacteria are inhibited by highly dilute or high osmolarity urine.
Bacteria enter epithelial cells and form intracellular bacterial communities.
Signs and Symptoms
Diagnosis is made primarily by history.
- history
- physical exam
History
Cystitis describes dysuria, frequency, urgency, and occasionally suprapubic pain.
Acute pyelonephritis is accompanied by
Infants and young children
fever above 38C, irritability, poor feeding, vomiting, diarrhea
First UTIs can be discriminated from recurrent UTIs.
Physical Exam
Percuss the back to assess for costovertebral angle (CVA) tenderness, suggesting possible kidney involvement.
Do back exam to look for scars, dimples, assymetric gluteal muscles, or a hairy patch as signs of neural tube defects.
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
As most community acquired UTIs are caused by E coli, diagnosis can be made clinically, with the help of urine dipsticks.
Dipsticks are easy to do at point-of care and reveal much good information, including:
- leukocyte esterase - released from broken-down leukocytes
- nitrites - produced by gram negatives, especially E coli, Klebsiella, and Proteus
Urine culture is indicated in complicated or hospital-induced infections. 100,000 CFU/ml (void) and 50,000 CFU/ml (catheter) are the traditional cut-offs for diagnosis.
Urine culture is usually positive for bacteria. Bacteriuria is a prerequisite, but does not necessarily represent clinical disease. The same can be said for pyuria. Significant bactiuria is usually defined as greater than 105 bacterial/ml, though lower number may be more important in children or catheter-collected specimens.
Serum tests are not the most reliable means of diagnosing infection, but do appear to represent host response to
Quantitative culture
- significant counts
- good quality specimens
- nitrate dip slide
Diagnostic Imaging
Differential Diagnosis
Treatments
Emperic therapy is often used, based on most probable pathogens, local rates of resistance, acute vs chronic infection, reinfection vs relapse, catheters, or others.
The treatment of choice for uncomplicated UTIs is a 3-day course of TMP-SMX.
Second-line treatments include:
- nitrofurantoin
- fluoroquinolones (contraindicated in pregnancy)
- amoxicillin
- first-generation cephalosporin
Pyelonephritis requires 2 weeks of treatment, while complicated infections or prostatitis require 6 weeks of treatment with a fluoroquinolone such as ciprofloxacin.
Under 3 months
Ampicillin and gentamycin are used to cover possible Listeria monocytogenes. IV treatment is generally continued 2-4 days after fever is gone, PO drug intake can be started, and C & S demonstrates antibiotic susceptibility.
Preventing UTIs
Maintain good hydration and urine output.
300ml cranberry (especially cranberry juice)
wipe urethra from front to back to avoid fecal contamination
avoid feminine hygeine sprays and douches
empty bladder immediately before and after intercourse
Consequences and Course
UTIs represent a wide range of clinical conditions, and signs and symptoms are often innacurate in identifying actual site of infection.
Uncomplicated infections occur in healthy people with structurally and functionally normal urinary tract, while complicated infections are associated with factors decreasing the chance of acquiring bacteria and decreasing the efficacy of therapy.
Asymptomatic bactiuria
Asymptomatic bactiuria need not necessarily be classified as a UTI, especially in older patients.
Asymptomatic bactiuria is always a concern in pregnant women or in patients undergoing invasive procedures of the urinary tract.
Cystitis
Cystitis is the most common UTI and represents infection confined to the bladder. While cyctitis Symptoms include:
- pain or burning during urination
- urgency or frequency
- no other signs or symptoms suggesting more widespread infection
Pyelonephritis
pyelonephritis is a diagnosis of more invasive infection. Involvement of the kindey and renal pelvis is associated with flank pain or tenderness. Fever, chills, nausea, malaise, headache may also be present
Prostatitis
Prostatitis is inflammation of the prostate gland and may be acute, chronic, or acute on chronic.
Intrarenal/perinephric abcess
A collection of pus in the kidney or surrounding tissue
Additional Resources
any good free online resources for further reading.
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