Question

A 21-year-old sexually active woman presented to the university student health service with a 2-day history of urinary frequency, urgency, dysuria, and evidence of blood in her urine. She had no prior history of urinary tract infection. Laboratory tests showed a slightly elevated white blood cell count of 10,500/uL, and the urine sediment contained innumerable white cells, suggestive of a urinary tract infection. Cultures yielded more than 10⁵ colony-forming units of a lactose-fermenting gram-negative rod. The most likely etiologic agent in this case is which of the following?

a) Klebsiella pneumoniae
b) Escherichia coli
c) Morganella morganii
d) Proteus mirabilis

Answer 1

The most likely etiological agent causing the UTI in this case is Escherichia coli (E. coli), as indicated by the presence of a lactose-fermenting gram-negative rod in the urine culture and associated symptoms and lab findings.

Step-by-step explanation:

The most likely etiological agent in this case is Escherichia coli (E. coli). This diagnosis is based on the laboratory results showing a lactose-fermenting gram-negative rod, which is a characteristic of E. coli, and the presence of white blood cells in the urine sediment suggestive of a urinary tract infection. E. coli is the most common cause of urinary tract infections (UTIs), and the presence of nitrites on a urine dipstick test can further indicate its presence, as this organism converts nitrates to nitrites.

The symptoms presented by the patient, such as urinary frequency, urgency, dysuria, and hematuria, along with an elevated white blood cell count and significant growth of bacteria in cultures, support the diagnosis of a UTI caused by E. coli.