A urinary tract infection (UTI) is an infection of any part of the urinary system, including the kidneys, ureters, bladder, and the urethra.
A UTI is defined as the presence of at least 100,000 organisms per mL of urine in an asymptomatic patient or more than 100 organisms per mL of urine with accompanying pyuria (greater than 7 WBCs/mL) in a symptomatic patient.
UTIs can be divided anatomically into upper and lower tract infections. UTIs affecting the kidneys or ureters are classified as upper tract infections and those affecting the bladder or urethra are classified as lower tract infections.
A complicated UTI is noted in a patient with a structural or functional urinary tract system or in a patient who is immunocompromised. Complicated UTIs may require parental therapy until afebrile.
The incidence of UTIs depends on age and gender.
Young males aged 15 to 50 years rarely develop UTIs.
The incidence of a UTI in geriatric males may be as high as in geriatric females (up to 15%).
The normal male urinary tract has many natural defenses to infection. The greater susceptibility of elderly males is related to problems with the prostate and other urologic disease.
More than 50% of women will have one UTI in their lifetime. Prevalence for females increases by 1% per decade and 2%-4% throughout childbearing years. The incidence of UTIs in pregnancy ranges from 4%-7%. In pregnancy, the increased incidence is related to both hormonal influence and anatomic changes that increase the risk of urinrary stasis and vesicoureteral reflex. With women, bacteria ascend from the perineum through the urethra. The greater susceptibility of younger women and girls is related to a shorter urethra. In older women, it is related to estrogen-mediated dilation of the urethra.
In children, the incidence also depends on age and gender. A UTI is the most common cause of fever of unknown origin in pediatrics.
Gram-negative bacilli are the most common pathogens; 80%-90% of cases are related to coliform bacteria (E. coli), which originates from fecal floras that colonize the periurethral area. Other gram-negative bacteria include Klebsiella penumoniae or Proteus mirabilis. Staphylococcus saprophyticus (gram-positive coccus) accounts for 10-15% of UTIs. Other pathogens include Enterobacter, Pseudomonas, Enterococci, and Staphylococci. The incubation period depends on the pathogen.
Risk factors for UTIs include the female gender (until elderly, then equal frequency in males and females), pregnancy, poor hygiene, trauma, instrumentation, sexual intercourse, oral contraceptive or diaphragm use, females with diabetes (no increased risk for male diabetics), anomalies of the genitourinary (GU) tract, neurologic factors, vesicourethral reflux, obstruction with stones, foreign bodies, bubble baths and hot tubs, douching, anal intercourse, HIV, uncircumcised penis, catheterization, nasocomial infection, and phimosis.
Common symptoms associated with UTIs include burning on urination, urinary frequency, cloudy or bloody urine, urinary urgency.
In UTIs seen in children, symptoms may be vague and may be with a fever or without a fever. Gastrointestinal symptoms may include vomiting and diarrhea. The child may have frequent voiding, incontinence, dysuria (pain on urination), and suprapubic, abdominal or lumbar pain.
In UTIs seen in the geriatric population, there may not be classic presentation of a UTI. The person may present with a fever, incontinence, and mental confusion.
It is important to remember during physical examination of a person with a UTI that the absence of a fever does not exclude a UTI.
The diagnosis of a UTI can often be made based on a focused history and the presenting symptoms.
One important diagnostic test is a urinalysis. A clean-catch urinalysis may be performed. If the patient is unable to collect a clean-catch specimen, catheterization or suprapubic aspiration may be necessary. The percutaneous bladder aspiration is used for young children and infants.
Urinalysis dipstick findings:
Appearance: The urine should be clear. Cloudy urine may indicate presence of pus, blood, cells, phosphate, or lymph fluid.
Odor: Usually faint aromatic odor. Ammonia odor indicates Proteus, related to food changes. Offensive odor indicates bacterial infection.
pH: The normal pH of urine is around 6 (acidic) and may vary from 4.6 to 7.5. Greater than 7.5 may indicate infection.
Specific gravity: Reflects the kidney's ability to concentrate urine and the body's hydration status. Normal range is 1.005 to 1.025.
Color: Shows concentration of urine and is usually yellow or amber.
Contents: Positive leukocyte esterase and nitrates indicate infection.
A negative urine dipstick does not rule out an infection.
Urine Culture & Sensitivity
Positive culture standard 10^5 CFU (colony-forming units), symptomatic female 10^2 CFU, and symptomatic males (10^3)
Screening for asymptomatic bacteria is recommended in pregnant women and for elderly males with documentated prostatic or urologic abnormalities, for patients with a recent catherization, and for patients with known stones or documented structural abnormalities.
Treatment of UTIs is aimed at identifying the underlying cause and initiating treatment as soon as possible.
If antibiotic therapy is initiated, stress the importance of taking all medication as directed, even if symptoms improve before the end of treatment.
Instruct the patient to increase fluids and to drink at least one large glass of liquid every hour.
Instruct the patient to avoid foods that irritate the bladder: caffeine, alcohol, tomatoes, citrus, and spicy foods.
Encourage the patient to drink cranberry juice to help fight bladder infections. If the patient dislikes the taste of pain cranberry juice, have him or her mix it 1:1 with another juice, such as orange juice.
The treatment for UTIs are antibiotics.
A 3-day course may be efficacious and is less expensive than the traditional 7- to 10-day course of therapy for uncomplicated infections.
The antibiotic of choice depends on the specific bacteria found on culture. Empiric antimicrobial therapy should cover all likely pathogens.
Nitrofurantoin monohydrate/macrocrystals (Macrobid) 100mg orally twice a day for 5 days
Trimethoprim/sulfamethoxazole 160mg/800mg (Bactrim DS, Septra DS) 1 tablet orally twice a day for 3 days (use when bacterial resistance is less than 20% and patient has no allergy)
Fosfomycin (Monurol) 3g orally ina single dose with 3 to 4 oz of water
Ciprofloxacin (Cipro) 250mg orally twice a day for 3 days
Ciprofloxacin extended-release (Cipro XR) 500mg orally twice a day for 3 days
Levofloxacin (Levaquin) 250mg orally twice a day for 3 days
Amoxicillin-clavulanate (Augmentin) 875mg/125mg orally twice a day for 7 days
Amoxicillin-clavulanate (Augmentin) 500mg/125mg orally three times a day for 7 days
Treatment in Children
Children younger than 2 years are usually treated for 7 to 14 days; children older than 2 years who are afebrile and without abnormalities of the urinary tract or have previous episodes of UTIs are usually treated for 5 days.
Amoxicillin-clavulanate (Augmentin): 20 to 45mg/kg orally per day every 12 hours
Sulfonamide-trimethoprim-sulfamethoxazole (Bactrim, Septra): 6 to 12 mg/kg trimethoprim and 30 to 60 mg/kg sulfamethoxazole per day orally in two doses
Cephalosporin-cefixime (Suprax): 8 mg/kg/d in one dose or in divided doses every 12 hours
Antibiotics that should not be used in pediatrics or pregnancy include the following:
Fluoroquinolones are not used in children because of potential concerns about sustained injury to developing joints.
Fluoroquinolones (Category Class C) are contraindicated during pregnancy because of auditory and vestibular toxicity in the fetus.
Tetracyclines should not be used in pregnancy (Category Class D) or in children because of tooth staining.
Nitrofurantoin is contraindicated in pregnant patients at term, during labor, and during delivery.
Glass, C. & Cash, J. (2017). Family practice guidelines 4th edition. New York: Springer Publishing Company.
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