Urinary Tract Infection

Article Author:
Michael Bono
Article Editor:
Wanda Reygaert
Updated:
11/15/2018 10:32:26 PM
PubMed Link:
Urinary Tract Infection

Introduction

Uncomplicated urinary tract infection (UTI) is a bacterial infection of the bladder and associated structures. These are patients with no structural abnormality and no comorbidities, such as diabetes, immunocompromised, or pregnant. Uncomplicated UTI is also known as cystitis or lower UTI. Forty percent of women in the United States will develop a UTI during their lifetime, making it one of the most common infections in women. UTI is uncommon in circumcised males, and by definition, any male UTI is considered complicated. Many cases of uncomplicated UTI will resolve spontaneously, without treatment, but many patients seek treatment for symptoms. Treatment is aimed at preventing spread to the kidneys or developing into upper tract disease/pyelonephritis, which can cause the destruction of the delicate structures in the nephrons and lead to hypertension.[1][2][3]

Etiology

Pathogenic bacteria ascend from the perineum, causing UTI. Women have shorter urethras than men and therefore are more susceptible to UTI. Very few uncomplicated UTIs are caused by blood-borne bacteria. Escherichia coli is the most common organism in uncomplicated UTI by a large margin.[4]

Epidemiology

Urinary tract infections are very frequent bacterial infection in women. They usually occur between the ages of 16 and 35 years, with 10% of women getting an infection yearly and more than 40% to 60% having an infection at least once in their lives. Recurrences are common, with nearly half getting a second infection within a year. Urinary tract infections occur four times more frequently in females than males.[5][6]

Pathophysiology

An uncomplicated UTI usually only involves the bladder. When the bacteria invade the bladder mucosal wall, cystitis is produced. The majority of organisms causing a UTI are enteric coliforms that usually inhabit the periurethral vaginal introitus. These organisms ascend into the bladder and cause a UTI. Sexual intercourse is a common cause of a UTI as it promotes the migration of bacteria into the bladder. People who frequently void and empty the bladder have a much lower risk of a UTI.[7]

History and Physical

Symptoms of uncomplicated UTI are a pain on urination (dysuria), frequent urination (frequency), inability to start the urine stream (hesitation), sudden onset of the need to urinate (urgency), and blood in the urine (hematuria). Usually, patients with uncomplicated UTI do not have fever, chills, nausea, vomiting, or back pain, which are signs of kidney involvement or upper tract disease/pyelonephritis. Clinical symptoms can overlap, and in some cases, it is hard to distinguish uncomplicated UTI from a kidney infection. When in doubt, treat aggressively for possible upper renal tract disease. Diagnosis is a combination of signs, symptoms, and urinalysis. Be careful of literature that is based on the results of urinalysis of asymptomatic patients.

Evaluation

A good, clean, urinalysis (UA) specimen is vital to the workup. A clean-catch specimen in nonobese women is preferred. Most obese women cannot give a clean specimen, and epithelial cells in the UA means the urine sample was exposed to the genital surface and did not come directly out of the urethra. Get a clean sample, with very few epithelial cells. In-and-out catheterization of the bladder will cause UTI in uninfected women 1% of the time. Men should start the urine stream to clean the urethra and then obtain a midstream sample. Urine should be sent to the lab immediately or refrigerated because bacteria grow rapidly when a sample is left at room temperature, causing an overestimate of the infection's severity.[8][9]

Do not base the diagnosis upon visual inspection of the urine. Cloudy urine can be aseptic; the cloudiness can come from protein in the sample, not necessarily infection. Crystal clear urine can be grossly infected. All urines undergo dipstick testing, which can be done at the bedside. Helpful values are pH, nitrites, leukocyte esterase, and blood. Remember that in patients with symptoms of UTI, a negative dipstick does not rule out UTI, but positive findings can help make the diagnosis. Look for the presence of bacteria and/or white blood cells (WBC) in the urine.

Normal urine pH is slightly acidic, with usual values of 6.0 to 7.5, but the normal range is 4.5 to 8.0. A urine pH of 8.5 or 9.0 is indicative of a urea-splitting organism, such as Proteus, Klebsiella, or Ureaplasma urealyticum; therefore, an asymptomatic patient with a high pH means UTI regardless of the other urine test results. Alkaline pH also can signify struvite kidney stones, which are also known as “infection stones.”

The most accurate dipstick test is the nitrite test because bacteria must be present in the urine to convert nitrates to nitrites. This takes 6 hours. This is why urologists request the first-morning urine, particularly in males. The specificity of this test is greater than 90%. This is direct confirmation of bacteria in the urine, which is UTI by definition in patients with symptoms. Several bacteria do not convert the nitrates to nitrites, but those are usually involved in complicated UTIs, such as those involving Enterococcus, Pseudomonas, and Acinetobacter.

Leukocyte esterase (LE) identifies the presence of WBCs in the urine. The WBCs release the LE, presumably in response to bacteria in the urine. This is why LE is a subsequent test with a specificity of only 55% for UTI. LE is good at detecting WBCs in the urine, but WBCs can be in the bladder for other reasons, like inflammatory disorders.

Hematuria can be helpful because bacterial infection of the transitional cell lining of the bladder can cause bleeding. This helps distinguish UTI from vaginitis and urethritis which do not cause blood in the urine.

In many labs, the presence of nitrites or leukocyte esterase will automatically trigger a microscopic evaluation of the urine for bacteria, WBCs, and RBCs. On microscopy, there should be no bacteria in uninfected urine, so any bacteria on a gram-stained urine under microscopy is highly correlated to UTI. A good urine sample with greater than 5 to 10 WBC/HPF is abnormal and highly suggestive of UTI in symptomatic patients.

Urine cultures are not needed in uncomplicated UTI. Urine should be cultured in all men and patients with diabetes mellitus, who are immunosuppressed, and women who are pregnant. Classic teaching on urine culture sets the gold standard for infected urine at greater than 10 colony forming units (CFU). Recent literature states that a patient who presents with symptoms and greater than 10 CFU is diagnostic of infection. Urine cultures rarely help in the emergency department, except with recurrent UTI.

Treatment / Management

Treatment has varied historically from 3 days to 6 weeks. There are excellent rates with “mini-dose therapy” which involves three days of treatment. E. coli resistance to common antimicrobials varies in different areas of the country, and if the resistance rate is greater than 50% choose another drug.

Trimethoprim/Sulfamethoxazole for 3 days is good mini-dose therapy, but resistance rates are high in many areas. First generation cephalosporins are good choices for mini-dose therapy. Nitrofurantoin is a good choice for uncomplicated UTI, but it is bacteriostatic, not bacteriocidal, and must be used for 5 to 7 days. Fluoroquinolones have high resistance but are a favorite of urologists for some reason. Recent precautions from the FDA about fluoroquinolone side effects should be heeded.[10][11][12]

Differential Diagnosis

  • Pyelonephritis
  • Renal stone
  • Vaginitis
  • PID
  • Herpes simplex

Pearls and Other Issues

Although there is no proof of prevention, women should urinate after sexual intercourse because bacteria in the bladder can increase by ten-fold after intercourse. After urination, women should wipe from front to back, not from the anal area forward, which seems to drag pathogenic organisms nearer to the urethra. Vigorous urine flow is helpful to prevention.

Enhancing Healthcare Team Outcomes

UTI is best managed in a multidisciplinary fashion, and besides physicians, most nurses will encounter a patient with a UTI. The key to preventing recurrences is the education of the patient. Once a UTI has been diagnosed the patient should drink more fluids. Sexually active women should try to void right after sexual intercourse as this can help flush the bacteria out of the bladder. Some women with recurrent UTIs may benefit from prophylactic use of antibiotics. Several other non-medical remedies may help some women with UTI. Anecdotal reports indicate that the use of cranberry juice and probiotics may help reduce the severity and frequency of UTI in some women.[13][14] (Level V)

Outcomes

The majority of women with a UTI have an excellent outcome. Following treatment with an antibiotic, the duration of symptoms is 2-4 days. Unfortunately, nearly 30% of women will have a recurrence of the infection. Morbidity is usually seen in older debilitated patients, those with renal calculi and in patients. Other factors linked to recurrence include the presence of diabetes, underlying malignancy, chemotherapy and chronic catheterization of the bladder. The mortality after a UTI is close to zero, but the infection does have a significant impact on finance. Women often have to miss work, see the physician and purchase the antibiotic. [15][16](Level V)