An anemic patient was transfused with packed red blood cells. Approximately one hour after the transfusion began, the patient developed fever and hypotension consistent with endotoxic shock. The red blood cells had been stored at 4°C for about 30 days before use. Which organism is most likely involved?

• A. Campylobacter fetus
• B. Pseudomonas aeruginosa
• C. Neisseria meningitidis
• D. Yersinia enterocolitica

Answer: (D)

The key idea is that certain bacteria can multiply in stored blood at refrigeration temperatures and cause a rapid septic transfusion reaction. Yersinia enterocolitica is psychrotrophic, meaning it can grow at 4°C, so it can proliferate in packed red blood cells stored for weeks. If contaminated blood is transfused, these bacteria release endotoxin (LPS) in the recipient’s circulation, leading to fever and hypotension consistent with endotoxic shock within a short time after transfusion.

Other organisms listed are less likely in this scenario: some do not thrive at refrigerated temperatures, and they are not the classic culprits associated with transfusion-related septicemia from stored blood. Therefore, Yersinia enterocolitica best explains the rapid fever and shock after transfusion of refrigerated blood.