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Quick Update: Infection Caused by Rifampin/Penicillin-Resistant Strain of RB51 Brucella Associated W

  • Read CDC HAN here:

  • Associated with raw milk from Miller’s Biodiversity Farm in Quarryville, PA

  • Third known case of brucellosis caused by Brucella RB51 (vaccine strain)

  • Diagnosed in November 2018

  • Milk samples from this dairy farm tested positive for Brucella abortus RB51

  • Potential exposures in 19 states (AL, CA, CT, FL, GA, IA, MD, MA, MI, MN, MS, NJ, NY, NC, OH, PA, RI, SC, VA)

  • Fun facts about RB51

  • Vaccination plays an important role in reducing brucellosis in cattle in the US, saving the industry hundreds of millions of dollars per year compared to pre-vaccination era

  • RB 51 is a live-attenuated vaccine strain derived from serial passaging of B. abortus

  • Lacks polysaccharide O-side chain hence decreased virulence in animals, but can still cause rare infection in human

  • Resistant to rifampin because serial passaging to create the strain was performed in growth media with rifampin

  • Although vaccinated cattle are protected, the RB51 vaccine does not generate measurable antibody, which saves the industry even more since you can’t really test for immune response (as opposed to its predecessor vaccine strain S19 which required post-vaccination testing)

  • The vaccine is still infectious and requires careful handing

  • Why it is not awesome for human to get infected by RB51

  • There is currently not a serological test to detect the presence of antibody against B. abortus RB51

  • CDC Lab Response Network (LRN)’s BMAT protocol for serological diagnosis of brucellosis can diagnose infections from field Brucella species, but not RB51

  • Since there is no serological test available, the only recommended approach to diagnosis in clinical labs is blood culture

  • You must let the lab know before submitting specimens to ensure safety of laboratory personnel!

  • Only LRN labs capable of performing Brucella PCR can detect the presence of RB51 in human directly from clinical specimens

  • Organism is rifampin- and penicillin-resistant

  • Data on effectiveness of PEP is lacking since there have been very few cases

  • More info on brucellosis here:

  • LRN sentinel lab protocol for Brucella spp.:

  • Don’t consume raw dairy product!

  • See this algorithm from the CDC

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