Urinary Tract Infection

Urinary tract infection (UTI) occurs when pathogenic bacteria enter the urethra and cause infection and inflammation. The urethra alone may be affected (urethritis), but more commonly the infection reaches the bladder (cystitis). The kidneys may also be involved (pyelonephritis), sometimes leading to complicated UTI, stone formation, and/or sepsis. The remainder of this chapter focuses primarily on acute, uncomplicated cystitis.

UTIs occur in all age groups. The bacterial pathogens predominantly originate from fecal flora. Escherichia coli (E coli) are the most common (≈ 85%). Staphylococcus saprophyticus, Klebsiella, Proteus, Enterococcus, Pseudomonas, and methicillin-resistant Staphylococcus aureus (MRSA) may also cause infection.

It has been noted that in some E coli-related urinary tract infections, the pathogenic bacteria appear to be foodborne. Using genetic matching techniques, researchers from several countries have found that pathogenic E coli in women with UTIs often originate in retail chicken products.[1],[2] The poultry counter appears to act as a reservoir for pathogenic E coli, a problem that may be aggravated by drug resistance related to the use of antibiotics on farms.

Cystitis is generally a clinical diagnosis, and radiologic investigation is not usually required except in certain cases involving children (e.g., when febrile, when known risk factors are present) or in males. The most common symptoms of cystitis are dysuria, frequency, and urgency and suprapubic discomfort. Urinary tract infections are frequently asymptomatic, however, particularly in the elderly. Pain in the suprapubic region may be reported, and hematuria and cloudy urine may occur as well. Patients with pyelonephritis typically present with fever spikes, nausea/vomiting, and costovertebral or flank pain.

In elderly persons, confusion and other mental status changes may be the only signs of a urinary tract infection. Among children, symptoms typically include irritability, changes in eating habits, incontinence, and diarrhea. Vomiting or sensation of incomplete voiding may be the only symptom in young girls.

Risk Factors

Gender. Females have UTIs more frequently than males because of a shorter urethra that is in closer proximity to the perineum. More than 50% of women will have a UTI during their lifetime, with 20% of these women experiencing 2 or more infections.[3] In men, UTIs are rare (less than 0.1%), except in cases of anatomic abnormalities.

Sexual intercourse. Recent intercourse raises the risk of UTI in women. Risk is increased with a new sexual partner, as well as with the use of spermicide.

Bladder catheterization.

Urinary tract obstruction. Prostatic enlargement (benign prostatic hyperplasia or cancer) or inflammation, nephrolithiasis, and other obstructions raise UTI risk.

Anatomic abnormalities. These may include ureterovesicular reflux.

Diabetes mellitus. Hyperglycemia and neurogenic bladder predispose to infection.

Postmenopausal. Atrophic urogenital changes after menopause increase risk.

Eating animal products. E. coli strains consumed through chicken, turkey, and pork have been matched to and likely cause some UTIs.[4]


The diagnosis of acute cystitis can usually be made by history alone. Acute onset of dysuria, urinary frequency, and absence of vaginal symptoms usually warrant empiric treatment. A urine dip or urinalysis (of a sample collected midstream) is an inexpensive way to help confirm suspicion, where leukocytes, red blood cells, and/or nitrites may be noted. False-positive and false-negative tests are frequent.

Urine culture is not indicated in an uncomplicated bladder infection unless resistance to standard antibiotic therapies is likely. In complicated and recurrent infections, a urine culture and sensitivity should be done. Standard urine cultures may be negative in urethritis caused by chlamydia. Blood cultures should be performed if complicated pyelonephritis is suspected, as bacteremia is present in about a third of cases.

Persons with recurrent or refractory infections may need diagnostic testing for anatomic abnormalities. This may require ultrasound, a spiral CT scan for kidney stones, intravenous pyelogram, cystogram, and cystoscopy.

Cigarette smokers with UTI, hematuria, and irritation during voiding should be evaluated for malignancy (transitional cell carcinoma) with CT intravenous pyelogram, cystoscopy, and urine cytology.


Asymptomatic bacteriuria does not necessarily require treatment; however, therapy is advisable for pregnant women, renal transplant recipients, and patients undergoing urological surgery.[5],[6]

Uncomplicated cases of urinary tract infection usually require a 3- to 7-day course of antibiotic therapy. A longer course may be necessary for patients with a history of UTI, immunocompromise, diabetes, or prolonged symptoms. For recurrent UTI, defined as 3 episodes of UTI in the preceding 12 months or 2 episodes in the preceding 6 months, longer treatment courses may be required. If recurrent UTI is linked to sexual intercourse, a single dose of antibiotic can be administered after sexual encounter.

Empiric Treatment for Uncomplicated UTI

Nitrofurantoin-macrocrystals, used twice a day for 5 days, are an effective treatment, and bacterial resistance is rare.

Trimethoprim/sulfamethoxazole (TMP/SMX), used twice a day for 3 days, is appropriate for empiric therapy if local resistance rates are < 20%, but prevalence of resistant bacteria is increasing.[7]

Fosfomycin trometamol is an option but is typically reserved for multi-drug resistant infections or when other first line options cannot be used.

Fluoroquinolones are less appropriate for empiric therapy because of their broad spectrum of bacterial coverage. In TMP/SMX-resistant bacteria, resistance to fluoroquinolones occurs more frequently than to nitrofurantoin.[8]

Uncomplicated UTI

Treatment based on culture and sensitivity will likely include one of the above drug classes. Cost-effective therapy with the narrowest-spectrum agent should be used.

Other possible antibiotics include sulfonamides, trimethoprim, and cephalosporins.

Complicated UTI

Fluoroquinolones (except for moxifloxacin) are first-line empiric agents. Nitrofurantoin and TMP/SMX are not appropriate empiric therapies due to high resistance rates.

Treatment usually is needed for at least 5-10 days and may require hospitalization and pathogen-focused drugs.


Fluoroquinolone antibiotics for 5-7 days are first-line options for outpatients with uncomplicated pyelonephritis in areas where local resistance is known to be < 10%.[7] When this class of antibiotics is contraindicated, a single dose of a parental antibiotic (e.g., 1g IM ceftriaxone) followed by an oral regimen of TMP/SMX, amoxicillin-clavulanate or a cephalosporin for 7-14 days is acceptable. Treatment should be narrowed or altered based on urine culture sensitivities.

Complicated pyelonephritis will require hospitalization and pathogen-focused intravenous antibiotics. These include ampicillin and gentamicin, TMP/SMX, fluoroquinolones, and third generation cephalosporins.


Various antimicrobial prophylactic regimens (continuous, intermittent, and post-coital) may help reduce or prevent recurrent UTIs. Voiding immediately after intercourse has not been proven helpful in reducing the risk of recurrent UTIs.

Phenazopyridine (Pyridium) is an analgesic that can be used for dysuria. It may turn the urine orange or red and give a false-positive nitrite test because of the discolored urine.

Nutritional Considerations

The role of diet in the prevention and treatment of urinary tract infection remains unsettled. As noted above, pathogenic bacteria originating in chicken products can pass through the intestinal tract before arriving at the urethra. It remains to be established whether avoiding contact with chicken could reduce UTI incidence.

Some nutritional strategies with anecdotal support (e.g., vitamin C, high intake of fluids) have not demonstrated clinical effectiveness. Others, such as cranberry juice, have proven effective in some clinical trials.[9] Still others, such as probiotic treatment and high-fiber diets, await further evaluation. In epidemiologic or clinical studies, the following factors are associated with reduced risk:

Breastfeeding. Secretory immunoglobulin A (sIgA) in breast milk prevents the translocation of intestinal bacteria across the gut mucosa by blocking interactions between bacteria and the epithelial lining of the gut. Breastfeeding also alters the colonization of the gut, achieving a reduced presence of the P-fimbriated type of E coli associated with higher risk for UTI.[10] Non-breastfed babies have been shown to have, on average, twice the risk for UTI compared with infants who were breastfed for at least 7 months. The benefit of breastfeeding is particularly large in girls. It may reduce the risk of UTI even after weaning.[9]

Flavonoid-containing juices. Certain classes of flavonoids (e.g., epicatechin) block adhesion of E coli fimbria to uroepithelial cells. They may also prevent UTI by other mechanisms, such as the downregulation of genes in E coli responsible for fimbrial expression. Epidemiologic and clinical studies show that women who consume cranberry or cranberry-lingonberry juices have a 20% lower risk for UTI compared with those not drinking juice, a finding comparable to that of continuous low-dose antimicrobial prophylaxis.[9],[11] The optimal dosage has not yet been standardized, nor is it clear which populations are most likely to benefit.[12],[13] Further research is therefore warranted.[14]

Lactobacilli. Limited evidence suggests that women who consume over the counter probiotic Lactobacilli have a significantly decreased risk (80% lower) for UTI.[15] Further research is needed to establish the most effective strains.[16]

High-fiber diets. Constipation is a risk factor for UTI and recurrent UTI, although the reasons are unclear.[17],[18] Clinical trials have not yet established the usefulness of dietary fiber for UTI prevention but increasing high-fiber foods in persons with low-fiber diets is a potentially beneficial strategy.


See Basic Diet Orders chapter.

Breastfeeding for at least 6 months, and longer if possible, is recommended.

For adults wishing to use flavonoid-containing juices as a preventive measure, cranberry juice consumed 3 times daily with meals would be appropriate.

What to Tell the Family

Urinary tract infection is often a combined result of a decreased ability to prevent opportunistic infection and the presence of a common (E coli) bacterial strain that travels from the gastrointestinal tract into the urethral opening. Infections are generally treated by antibiotics to prevent kidney damage.


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Last updated: April 14, 2023