Discussion

Incidence, risk factors and symptoms:

It is critically important to distinguish between true UTI and presence of bacteria in the urine in the absence of clinical signs and symptoms of infection, or asymptomatic bacteriuria (ASB).[1] The exact incidence of UTIs in female patients is poorly defined in the United States and is impacted by age and sexual activity. Among young, healthy, sexually active women there are approximately 0.5 episodes per person per year.[2] The incidence increases substantially when presenting with genitourinary signs and symptoms.[3,4] Urinary tract infections in this patient population, are exceedingly common with a lifetime incidence of appropriately 50%.[2,5]

The primary risk factor for developing a UTI is having a previous diagnosis of UTI, or recurrent UTI. Recurrent UTIs are defined as three or more infections in the previous 12 months or two or more infections in the previous 6 months.[6] upwards of 25% of patients will have a recurrent UTI within 6 months.[2,5] Cystitis (lower tract UTI) has the following symptoms: dysuria with or without frequency, urgency, and suprapubic pain.[3,7,8,9] Urinary frequency tends to be the most common symptom, especially when presenting with a sudden or severe onset.

Test sensitivity & specificity

The sensitivity and specificity of urine cultures in the diagnosis has been reviewed elsewhere. These numbers are relatively reliable for uncomplicated cystitis.[10,11] Urine cultures have a high clinical sensitivity and specificity among female patients presenting to an outpatient facility urine cultures. Urine cultures had a sensitivity of ~90% for UTI in healthy outpatient women. Different parameters from urinalysis (UA) can also be evaluated to assist in diagnosis of UTI. No combination of parameters has been found to extensively improve sensitivity or specificity. When examining UA parameters, those that measure presence of pyuria tend to have a high negative predictive value.[10,11] Notably, all studies of the UA tend to use a laboratory gold standard of a positive culture, and not a clinical gold standard of UTI. To account for the role of missing asymptomatic bacteriuria, we adjusted the reported sensitivity of WBC and leukocyte esterase. Assuming approximately 5% of healthy women have asymptomatic bacteriuria, we adjusted sensitivity to 89% for WBC >10 and 87% for LE > 1+.