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Notice to Readers: Potential Exposure to Attenuated Vaccine Strain Brucella abortus RB51 During a Laboratory Proficiency Test --- United States, 2007

On November 27, 2007, CDC was notified by New York State Department of Heath (NYSDOH) officials of potential Brucella abortus RB51 (RB51) exposures to laboratorians at a state laboratory from an isolate used in a recent Laboratory Preparedness Survey (LPS). RB51 is an attenuated vaccine strain of B. abortus used to vaccinate cattle against brucellosis; human illness is known to have resulted from RB51 vaccine--related exposures (1). The LPS is a voluntary proficiency-testing program developed jointly by the College of American Pathologists (CAP), Association of Public Health Laboratories (APHL), and CDC. The program is designed to exercise protocols for "rule-out" or "referral" of potential bioterrorism agents. During the October--November LPS exercise, 1,316 laboratories participated. Written LPS instructions instructed laboratories to handle and manipulate all samples under a Class II Biological Safety Cabinet (Class II BSC), using Biological Safety Level 3 (BSL3) primary barriers. The reported exposures occurred when an LPS RB51 specimen was mislabeled as a routine patient specimen and was submitted by an LPS participating laboratory to the New York state bacteriology laboratory. As a result, routine benchtop procedures were used to handle the isolate by NYSDOH lab personnel outside of the Class II BSC, resulting in 24 laboratorians with potential exposure to RB51. After this incident, NYSDOH contacted all New York LPS-participating laboratories to determine whether other exposures had occurred. Of the participating laboratories contacted, 80% had performed at least one procedure outside of the Class II BSC, despite the LPS written instructions outlining appropriate biosafety handling practices.

CDC was consulted and recommended that those laboratorians who conducted procedures with exposures placing them at high risk receive postexposure prophylaxis. The findings in New York also raised concern that participating laboratories outside of the state might not have followed all prescribed biosafety instructions, possibly exposing other laboratory personnel to RB51. CDC is collaborating with CAP, APHL, and public health officials to 1) determine exposure risk in participating laboratories, 2) provide interim guidance on risk assessment and postexposure prophylaxis recommendations, 3) identify any illnesses associated with potential RB51 exposures among laboratorians participating in the LPS, and 4) identify follow-up actions and the need for additional guidance (e.g., education or training).

During December 3--10, 2007, CDC took steps to provide information regarding the RB51 incident to public health officials. State public health officials were notified via a broadcast e-mail and through an alert on the Epidemic Information Exchange (Epi-X). National conference calls were conducted with state public health laboratory directors and state epidemiologists to provide interim guidance on risk assessment and postexposure prophylaxis recommendations. Formal notification was sent by overnight letter from CAP to all participating LPS laboratories. Laboratories were recommended to review their biosafety practices during handling of RB51 specimens and report breaches in biosafety practices to their local public health officials for risk determination and recommendations. A set of questions was distributed to facilitate review of biosafety practices used during the LPS to identify potentially exposed persons. Laboratories were advised to ensure their ability to comply with standard biosafety protocols as defined in Biosafety in Microbiological and Biomedical Laboratories, 5th Edition* and to take steps to avoid specimen handling errors. To date, CDC has not learned of any illness consistent with brucellosis in any laboratory staff member potentially exposed to an LPS RB51 isolate.

For information regarding risk assessments and postexposure prophylaxis recommendations for potentially exposed persons, laboratories can contact state or local health officials. Information regarding B. abortus RB51 is available at the CDC Bacterial Zoonoses Branch, telephone 404-639-1711, or the CDC brucellosis website. Public health officials can access updated information and risk assessment tools in Epi-X forum, "Brucella abortus/RB51 Exposure." Specific questions regarding the LPS can be directed to the CAP website§ or hotline, 800-443-3244. Questions regarding laboratory biosafety procedures can be directed to the CDC Laboratory Response Network, by e-mail,, or telephone, 866-576-5227.


  1. Ashford D, di Pietra J, Lingappa J, et al. Adverse events in humans associated with accidental exposure to the livestock brucellosis vaccine RB51. Vaccine 2004;22:3435--9.

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Date last reviewed: 12/20/2007


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