Pyelonephritis is a serious infection that manifests with fever, back pain, nausea, and vomiting. In the U.S., it is estimated that there are 20 cases of pyelonephritis per 10,000 annually, with the highest incidence in young women. Escherichia coli (E. coli) causes over 80% of these infections. Over the last two decades, E. coli resistance has emerged to commonly prescribed antimicrobials, such as ampicillin and trimethoprim-sulfamethoxazole (TMP/SMX). Most recently, resistance to fluoroquinolones and strains producing extended-spectrum beta-lactamases (ESBL) have been observed. In order to better understand the evolution and current state of antibiotic resistance among E. coli urinary tract isolates so as to better inform treatment decisions, the investigators propose to conduct an investigation to: a) determine the prevalence of antimicrobial resistance among E. coli causing acute pyelonephritis in various patient groups, and specifically healthy community-dwellers with uncomplicated infections, b) determine the specific prevalence of fluoroquinolone-resistance and ESBL-producing E. coli, and c) determine potential risk factors for fluoroquinolone and ESBL-producing E. coli infections.

Inclusion Criteria:

• patients > 18 years of age with flank pain and/or costovertebral angle tenderness
• documented temperature in the emergency department of ≥38°C/100.4°F by any method of measurement,
• documented temperature in the emergency department of ≥38°C/100.4°F by any method of measurement,

Exclusion Criteria:

• complicated pyelonephritis

Patients will be recruited from ten U.S. university-affiliated medical center emergency departments participating in a CDC-collaborative emerging infections sentinel network, EMERGEncy ID NET. Patients presenting with symptoms of acute uncomplicated pyelonephritis will be enrolled by treating physicians or study coordinators.