A 22-Year-Old Woman Comes to the Office Due to Dysuria

A 22-year-old woman comes to the office due to dysuria and urinary frequency.  She has had no fever, chills, nausea, or vomiting.  In the last 8 months, the patient has had 2 urinary tract infections that began shortly after intercourse, despite immediate postcoital voiding.  The first infection was complicated by pyelonephritis that responded to oral antibiotics; urine culture at that time grew pan-susceptible Escherichia coli.  She has no other medical problems and has had no surgeries.  Current medications include oral contraceptives.
Vital signs are normal.  There is mild suprapubic tenderness but no costovertebral angle tenderness.
Urinalysis results are as follows:
In addition to oral antibiotics for the current infection, which of the following is the best next step in management of this patient?

A) Change in contraception to diaphragm plus spermicide
B) Cranberry supplementation
C) Excretory urography and cystoscopy
D) Postcoital antibiotic prophylaxis
E) Renal ultrasound