The Report Said Susceptible

A 67-year-old woman with pancreatic adenocarcinoma diagnosed three months ago presents to the emergency department with two days of fever, right upper quadrant pain, jaundice, and rigors. She underwent endoscopic retrograde cholangiopancreatography (ERCP) with biliary stent placement for malignant distal common bile duct stricture seven weeks ago. A second ERCP with stent exchange was performed two weeks ago for recurrent jaundice. She completed a 7-day course of levofloxacin after the first ERCP but has received no antibiotics since.

On examination her temperature is 39.4 C, heart rate 124/min, blood pressure 82/50 mmHg, respiratory rate 22/min, and oxygen saturation 97% on room air. She is icteric, diaphoretic, and diffusely tender in the right upper quadrant with voluntary guarding. There is no peritoneal sign. A right internal biliary stent is known to be in place.

Laboratory studies show white blood cells 18.6 x 10^3/uL with 84% neutrophils and 8% bands, total bilirubin 6.8 mg/dL (direct 5.4), alkaline phosphatase 384 U/L, ALT 112 U/L, AST 98 U/L, creatinine 1.4 mg/dL (baseline 0.8), lactate 4.2 mmol/L, and C-reactive protein 196 mg/L. CT abdomen shows a patent biliary stent with upstream intrahepatic and extrahepatic ductal dilatation, periductal stranding, and a small amount of perihepatic fluid consistent with cholangitis.

Blood cultures are drawn and empiric piperacillin-tazobactam is started. ERCP with stent exchange and biliary drainage is performed urgently. On hospital day 2, both blood culture sets grow gram-negative bacilli. The organism is identified by MALDI-TOF MS as Klebsiella aerogenes (formerly Enterobacter aerogenes).

Antimicrobial susceptibility testing returns on hospital day 3:

• Ampicillin/sulbactam: Resistant
• Piperacillin/tazobactam: Susceptible (MIC <= 8)
• Ceftriaxone: Susceptible (MIC <= 1)
• Ceftazidime: Susceptible (MIC 2)
• Cefepime: Susceptible-dose dependent (MIC 4 mcg/mL)
• Aztreonam: Susceptible (MIC 2)
• Ertapenem: Susceptible (MIC <= 0.5)
• Meropenem: Susceptible (MIC <= 0.25)
• Gentamicin: Susceptible
• Ciprofloxacin: Resistant
• Levofloxacin: Resistant
• Trimethoprim/sulfamethoxazole: Susceptible

The patient remains on piperacillin-tazobactam. She is afebrile after ERCP and source control, hemodynamically improved on intravenous fluids, and her bilirubin is trending down. The primary team reviews the susceptibility report and considers narrowing from piperacillin-tazobactam to ceftriaxone, which the report lists as susceptible.