Urinary tract infections (UTIs) are the most common bacterial infections treated in the outpatient setting. More than 50% of women experience one in their lifetimes, and approximately 12% of women have a UTI annually. UTIs are divided into two major categories: lower tract infections and upper tract infections. Lower UTIs include urethritis, typically caused by sexually transmitted diseases and differentiated by the presence of discharge, and cystitis, an acute bacterial infection of the urinary bladder. Pyelonephritis is an infection of the upper urinary tract structures including the ureters and kidneys. Differentiation of upper and lower UTIs is based on history and physical exam.
Uncomplicated UTI occurs in young, healthy, nonpregnant women with structurally and functionally normal urinary tracts.
Complicated UTI occurs in patients who are older, healthy, nonpregnant women with normal urinary tracts: that is, all men, and women who have a structural or functional genitourinary abnormality or an underlying predisposing medical condition that increases the risk of infection and recurrence or reduces the effectiveness of antimicrobial therapy.
Asymptomatic bacteriuria (ABU) is the presence of significant bacteria in urine without signs or symptoms that are referable to a urinary tract infection; the usual cutoff is a single organism isolated in a quantity of at least 100,000 colony forming U/mL. Screening and treatment is not generally recommended, with the exception of women who are pregnant or men who are going to undergo a transurethral prostate resection.
More than 80% of UTIs are caused by Escherichia coli. Other causative organisms include Klebsiella, Proteus, Enterobacter, Pseudomonas, Chlamydia, and Staphylococcus saprophyticus.
Typical symptoms of cystitis include frequency, urgency, hesitancy, and suprapubic pain. Pyelonephritis is characterized by the addition of flank pain or costovertebral angle tenderness, particularly in conjunction with fever, chills, or nausea and vomiting. If vaginal or urethral discharge is present, urethritis, vaginitis, cervicitis, or PID are more likely than UTI. As in many diseases, diabetics and the elderly have a predilection for presenting atypically, and weakness, malaise, generalized abdominal pain, or altered mental status may be the only signs or symptoms noted.
Diagnosis and Differential
Diagnosis of UTI can be inferred from history and physical, and confirmed by urine dipstick or urinalysis and culture. Clean-catch midstream collection of urine is as accurate as urine obtained by catheterization if the patient follows instructions carefully. Catheterization should only be used in a patient that cannot void spontaneously, is too ill or immobilized, or is extremely obese. Note that 1% to 2% of patients develop a UTI after a single catheter insertion.
The two tests of interest on urine dipstick are nitrite reaction, a measure of bacteriuria, and leukocyte esterase, a measure of pyuria. Nitrite has a very high specificity (>90%), but a ...