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Chapter 24: Urinary Tract Infections

GB is a 28-year-old woman with a chief complaint of dysuria. Symptoms started three days ago. The physician orders a urinalysis and a urine culture. What is the most likely bacterial cause of the UTI?

a. Acinetobacter baumannii

b. Escherichia coli

c. Pseudomonas aeruginosa

d. Staphylococcus saprophyticus

Answer b is correct. The majority of UTIs are caused by gram-negative bacteria, of which E. coli is the most common pathogen.

Answer a is incorrect. Acinetobacter baumannii is a nosocomial organism and a cause of catheter-associated UTIs.

Answer c is incorrect. Pseudomonas aeruginosa is a nosocomial organism and causes less than 20% of UTIs.

Answer d is incorrect. Staphylococcus saprophyticus only causes 5% to 10% of uncomplicated UTIs. It is the most common gram-positive bacteria causing uncomplicated UTIs.

What is appropriate empiric therapy for GB? Patient has normal renal function and no medication allergies. Medications include metoprolol and omeprazole.

a. Cefdinir

b. Linezolid

c. Amoxicillin


Answer d is correct. TMP-SMX is appropriate empiric therapy for GB. If the local E. coli resistance rate for TMP-SMX is high, ciprofloxacin would be an appropriate choice.

Answer a is incorrect. Cefdinir is an oral third-generation cephalosporin commonly used for acute otitis media in pediatrics. It is not indicated for treatment of UTIs. While cefdinir is not indicated for treatment of urinary tract infections, you may see an oral cephalosporin utilized. Bacteria are becoming increasingly more resistant and management is driven by in vitro results of a culture and susceptibility report. There are often times when an E. coli UTI is resistant to SMZ/TMP and quinolones; therefore, alternative therapy may be utilized (even if it is not indicated).

Answer b is incorrect. Linezolid is an antibiotic that covers gram-positive bacteria exclusively. It is primarily used to treat methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). Both MRSA and VRE can cause UTIs, but GB does not need to be empirically covered with linezolid.

Answer c is incorrect. Escherichia coli resistance rate to amoxicillin is high (37% and higher in select regions). Therefore, aminopenicillins (eg, amoxicillin) would not be ideal for empiric therapy. Because E. coli and other fermenting gram negative rods (eg, Klebsiella) produce beta lactamase, the addition of clavualnate to amoxicillin (Augmentin) may be utilized in the treatment of E. coli UTIs.

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