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Community-onset urinary tract infections (UTIs) caused by extended-spectrum β-lactamase (ESBL)–producing Enterobacteriaceae, which are resistant to ceftriaxone and usually coresistant to fluoroquinolones, are increasing worldwide. We investigate and describe in detail UTIs caused by ESBL-producing Enterobacteriaceae in our emergency department (ED), and determine the proportion that occurred in patients without health care–associated risk factors and who received discordant initial antibiotic therapy.At an urban public hospital in Northern California, microbiology staff prospectively reviewed ED urine culture results weekly for 1 year and presumptively identified ESBL-producing isolates by ceftriaxone plus ceftazidime resistance. For isolates associated with a clinical UTI, patient demographic and case clinical features were abstracted retrospectively. Health care–associated infections were defined by standard risk factors plus aged 65 years or older, bladder catheter, urologic procedure, functional dependence, or antibiotics in the previous 90 days. Community-associated infections were defined by absence of these. A subset of community-associated ESBL-producing Escherichia coli isolates underwent genotyping. Electronic health record query was used to determine the denominator of ED UTI patients who underwent urine culture during the study period.Between August 2016 and July 2017, there were 1,045 unique ED patients diagnosed with a UTI, whose specimens underwent culture. There were 62 ESBL-producing isolates (5.9%; 95% confidence interval [CI] 4.6% to 7.5%). Selected characteristics of the entire ESBL UTI cohort were median age 50 years, 37 (60%) patients were women, 28 (44%) Hispanic, 11 (18%) had been hospitalized in the previous 3 months, 19 (31%) had pyelonephritis, 49 (79%) of isolates were E coli, 44 (71%) were levofloxacin-resistant, and 24 (23%) nitrofurantoin-resistant. Initial antibiotic choice was discordant with isolate susceptibility in 26 of 56 cases (46%; 95% CI 33% to 60%), and the initial oral antibiotic prescred was discordant in 19 of 41 cases (46%; 95% CI 31% to 63%). Twenty-seven infections (44%; 95% CI 31% to 57%) were categorized as community-associated. Eight patients with community-associated infection were women younger than 50 years, with no comorbidities and no more than 1 UTI in the previous year. Of 12 community-associated E coli isolates tested, all were confirmed to harbor ESBL genes; the CTX-M1 β-lactamase gene was found in 8 (67%); 4 belong to genotype ST131.At this single Northern California ED, greater than 5% of culture-proven UTI were caused by ESBL-producing Enterobacteriaceae, and in nearly half of cases there was no identifiable health care–associated risk factor. Levofloxacin co-resistance and discordant antibiotic therapy were common.