A urinary tract infection (UTI) is the presence of urinary microorganisms that cannot be accounted for by contamination. UTIs occur in all individuals, but age, sex, pregnancy, diabetes, urinary catheter, and vaginal intercourse increase the risk of development. UTIs are divided into cystitis (lower tract and bladder) and pyelonephritis (upper tract and kidneys). Cystitis symptoms include dysuria, frequency, urgency, and occasionally suprapubic tenderness. Pyelonephritis is characterized as cystitis symptoms plus fever, flank pain, nausea, and vomiting. Elderly patients frequently do not experience specific urinary symptoms, but may present with altered mental status, change in eating habits, or gastrointestinal symptoms. In addition, patients with indwelling catheters or neurologic disorders commonly will not have lower tract symptoms. Instead, they may present with flank pain and fever.
Uncomplicated UTIs are infections occurring in women of childbearing age with structurally and neurologically normal urinary tracts. Complicated UTIs occur in patients with functional or structural abnormalities. In general, UTIs in men, pregnant women, children, and patients in health care-associated settings are considered complicated.
Symptoms are unreliable for the diagnosis of bacterial UTIs. A UTI diagnosis requires a patient with a positive urinalysis and urine culture. A urinalysis will identify pyuria, which is defined as greater than or equal to 10 leukocytes/mm3 of urine. Pyuria is nonspecific, and patients with pyuria may not have an infection (note the urine in the bladder is normally sterile). Patients with a UTI usually have greater than or equal to 105 bacteria/mL identified by culture. Any organism colonizing the urinary tract can cause a UTI, but most are caused by bacteria. The majority of uncomplicated UTIs are caused by gram-negative bacteria, with Escherichia coli being isolated in 70% to 95% of cultures. The most common gram-positive bacteria isolated are Staphylococcus saprophyticus and enterococci (Table 24-1).
TABLE 24-1Bacterial Causes of UTIs |Favorite Table|Download (.pdf) TABLE 24-1Bacterial Causes of UTIs
| ||Uncomplicated (%) ||Complicated (%) |
|Escherichia coli ||70-95 ||21-54 |
|Proteus mirabilis ||1-2 ||1-10 |
|Klebsiella spp ||1-2 ||2-17 |
|Citrobacter spp ||<1 ||5 |
|Enterobacter spp ||<1 ||2-10 |
|Pseudomonas aeruginosa ||<1 ||2-19 |
|Other ||<1 ||6-20 |
|Staphylococcus saprophyticus ||5-10 ||1-4 |
|Enterococci ||1-2 ||1-23 |
|Group B streptococci ||<1 ||1-4 |
|Staphylococcus aureus ||<1 ||1-2 |
|Other ||<1 ||2 |
Asymptomatic bacteriuria is the isolation of bacteria in an appropriately collected urine specimen obtained from a person without symptoms. The diagnosis of asymptomatic bacteriuria should be based on results of a urine culture. Pyuria accompanying asymptomatic bacteriuria is not an indication for therapy. Pregnant women should be screened for bacteriuria by urine culture at least once during early pregnancy (12-16 weeks gestation) or at their first prenatal visit. All positive urine cultures, including asymptomatic bacteriuria, should be treated in pregnant women. Screening for and treatment of asymptomatic bacteriuria before transurethral resection of the prostate is recommended.
The following regimens may be considered for prophylaxis ...