Protocol for diagnosis of urinary tract infection: reconsidering the criterion for significant bacteriuria

The traditional criterion of 10(5) colony-forming units (CFU) per milliliter of urine to diagnose urinary tract infection was based on studies of pregnant and nonpregnant women with asymptomatic bacteriuria or acute pyelonephritis. Recent studies of symptomatic women revealed that urine cultures in approximately one third of those with confirmed urinary tract infections grew only 10(2) to 10(4) CFU/mL. The major causes of acute dysuria among such women are urinary tract infection, sexually transmitted disease, and vaginitis. In most instances, it is possible to make the diagnosis based on clinical features. The major features of urinary tract infection are internal dysuria; frequency, urgency, and voiding of small volumes; abrupt onset; suprapubic pain; presence of pyuria. Presence of hematuria which occurs in about 50 percent of patients strongly suggests bacterial cystitis. Three to seven days of empiric antimicrobial therapy is indicated for these patients, with selection of a first-line antimicrobial agent that offers efficacy against Escherichia coli or Staphylococcus saprophyticus; reasonable cost; few side effects. Ampicillin is not recommended. Indications for culture include uncertain clinical features; history of previous infection within the past three weeks; duration of symptoms of more than seven days; recent hospitalization or catheterization; pregnancy; diabetes. To maximize the sensitivity and specificity of the urine culture in acutely symptomatic women, it is necessary to request the laboratory to report 10(2) to 10(4) CFU/mL.