A 23-year-old female presents to the ED with sudden onset of…

A 23-year-old female presents to the ED with sudden onset of flank and back pain, dysuria, and urgency. She is febrile and has chills, nausea, and headache. She reports no illnesses in the preceding weeks, and she currently is not taking any medications. A urinalysis is ordered, and the results are as follows:  Physical Examination Chemical Examination Microscopic Examination Color: Yellow Clarity: Cloudy                 Sp. Gr. 1.010 pH 5.5 Blood: Trace Protein: Trace LE: Positive Nitrite: Positive Glucose: Negative Ketones: Negative Bilirubin: Negative Urobilinogen: 1.0 EU 50-75 WBCs; clumps Macrophages noted 5-10 RBCs 2-4 Renal epithelial cells 2+ Bacteria Casts: 3-6 WBC/lpf 0-2 Granular  Based on the clinical signs and symptoms and the UA results, the most likely diagnosis is: