P‐BB‐3 | A Case of <i>Brucella abortus</i> RB51‐Positive Platelet Unit Culture

Eligibility requirements for apheresis platelet donors include “feeling well” on the day of donation, completing an abbreviated physical exam and completing the donor questionnaire which includes a donor's history of receiving live vaccines. We report the first case of Brucella abortus RB51 bacteria from a live attenuated cattle vaccine strain contaminating a platelet donation. The RB51 vaccine strain is approved to control brucellosis transmission in cattle in the United States. In October 2022, a 65-year-old male donor, with a 104 platelet-donation history, donated apheresis platelets. The donor was in good health and met all eligibility criteria. He had no other relevant medical conditions and was not taking any medications. He is self-employed as a large animal veterinarian, mostly involved in cattle work, regularly administering animal vaccinations including RB51 as well as assisting birthing in cattle and pigs. Donor reported no recognized breaks in infection control. He has no pertinent travel history, nor does he work with animals from outside the United States. Additionally, he denied consumption of unpasteurized dairy products and had no recognized parenteral exposures to animals or biologics. A single product was collected on a Trima Accel V7 (Terumo BCT, Lakewood CO). The unit underwent large volume delayed sampling (BacT\Alert, bioMérieux, Durham, NC). The anaerobic bottle was positive at 3 days, 17 h after inoculation. The initial Gram stain reported “no organisms seen.” After additional incubation, the final Gram stain interpretation from the blood was “gram negative rods.” The isolate was subsequently identified by biochemical and molecular testing as the Brucella abortus RB51 vaccine strain, which is rifampicin resistant, confirmed by whole genome sequencing at the Centers for Disease Control and Prevention's Bacterial Special Pathogens Branch. The donor was notified, referred to an infectious disease specialist and treated with doxycycline (100 mg BID) and trimethoprim/sulfamethoxazole (160 mg/800 mg BID) for 28 days. Clinical blood cultures were negative prior to, and remained negative, after treatment. The donor was indefinitely deferred until the regimen was complete with release from medical care, plus an additional 1 year. The donated unit was interdicted prior to transfusion. This case represents an unrecognized occupational exposure to the B. abortus RB51 attenuated vaccine strain, though the exact mechanism of transmission remains unclear. This case highlights the importance of bacterial strain identification in assessing epidemiologic risks and proper therapy, a potential weakness of current donor screening practices for higher-risk occupational groups

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