Urinary tract infections are the most common outpatient infections, but predicting the probability of urinary tract infections through symptoms and test results can be complex. The most diagnostic symptoms of urinary tract infections include change in frequency, dysuria, urgency, and presence or absence of vaginal discharge, but urinary tract infections may present differently in older women. Dipstick urinalysis is popular for its availability and usefulness, but results must be interpreted in context of the patient's pretest probability based on symptoms and characteristics. In patients with a high probability of urinary tract infection based on symptoms, negative dipstick urinalysis does not rule out urinary tract infection. Nitrites are likely more sensitive and specific than other dipstick components for urinary tract infection, particularly in the elderly. Positive dipstick testing is likely specific for asymptomatic bacteriuria in pregnancy, but urine culture is still the test of choice. Microscopic urinalysis is likely comparable to dipstick urinalysis as a screening test. Bacteriuria is more specific and sensitive than pyuria for detecting urinary tract infection, even in older women and during pregnancy. Pyuria is commonly found in the absence of infection, particularly in older adults with lower urinary tract symptoms such as incontinence. Positive testing may increase the probability of urinary tract infection, but initiation of treatment should take into account risk of urinary tract infection based on symptoms as well. In cases in which the probability of urinary tract infection is moderate or unclear, urine culture should be performed. Urine culture is the gold standard for detection of urinary tract infection. However, asymptomatic bacteriuria is common, particularly in older women, and should not be treated with antibiotics. Conversely, in symptomatic women, even growth as low as 102 colony-forming unit/mL could reflect infection. Resistance is increasing to fluoroquinolones, beta-lactams, and trimethoprim-sulfamethoxazole. Most uropathogens still display good sensitivity to nitrofurantoin. First-line treatments for urinary tract infection include nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole (when resistance levels are <20%). These antibiotics have minimal collateral damage and resistance. In pregnancy, beta-lactams, nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole can be appropriate treatments. Interpreting the probability of urinary tract infection based on symptoms and testing allows for greater accuracy in diagnosis of urinary tract infection, decreasing overtreatment and encouraging antimicrobial stewardship.
Keywords: antibiotic resistance; asymptomatic bacteriuria; diagnostic performance; dipstick urinalysis; likelihood ratio; microscopic urinalysis; symptoms; urinary tract infection; urine culture; women.
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