Exposure To Brucella In Clinical Microbiology Laboratory Workers: Acceptability Of Antibiotic Prophylaxis

Background: Microbiology laboratory workers (MLWs) are at risk for occupational exposure to infectious agents. Although brucellosis is uncommon in the United States, exposure to Brucella spp. is a common bacterial exposure reported in MLWs. 

Objective: To report workup and outcomes of exposure to Brucella in MLWs at the University of Wisconsin Hospital and Clinics (UWHC).

Methods: An exposure investigation was undertaken in response to a lab exposure to Brucella spp.

Results: In July 2010, the infection control department was notified that a patient's blood culture isolate was preliminarily identified as Brucella spp. Subsequent testing by the CDC confirmed Brucella melitensis. The patient was a 28 year old Mexican male who was admitted with lymphocyte-predominant meningitis. A blood culture was positive for Brucella spp. The patient was started empirically on doxycyline, improved clinically and was discharged.  He has subsequently been lost to followup.

We learned that an exposure had occurred in the microbiology laboratory when a microbiologist manipulated the isolate on the open lab bench to perform a gram stain and catalase test, an aerosol generating procedure. Standard laboratory procedures dictate that all plates be taped shut, with subsequent manipulations of the isolate done in a biological safety cabinet, if gram stain of blood culture reveals bacteria suspicious for Brucella. 

A root cause analysis in this case found that coagulase-negative Staphyloccocus had been recovered from earlier blood culture from this patient. The slower growing colonies (later identified as Brucella) were assumed to be likely Staphylococci and work was performed on the open bench. Using CDC criteria to define risk categories, a total of 18 staff sustained a potential exposure, with 17 meeting criteria for high risk exposure. All potentially exposed individuals underwent serial serologic testing at the WI State Lab of Hygiene at baseline and 2, 4, 6 weeks to detect subclinical infection and continue to receive weekly symptom checks with none reporting symptoms of brucellosis.  All staff received written information regarding risk of brucellosis, and discussion with the hospital epidemiologist was offered as a resource to address questions and concerns. Eleven (61%) of 18 MLWs accepted prophylaxis, 5 (28%) declined because of concern over side effects and 2 (11%) deferred pending pregnancy testing. All serological tests for Brucella on exposed employees were negative at weeks 0, 2, 4 and 6. Final serologic screening timepoint is 24 weeks (January 2011).

Conclusions: Acceptability of antibiotic prophylaxis among MLWs exposed to Brucella is suboptimal. Efforts to prevent exposure include strict adherence to biosafety lab practices. At our institution,  lab practice changed so that once taped, all plates are handled in a biosafety cabinet regardless of whether a less pathogenic organism is later recovered.