Outbreak of Brucella melitensis among microbiology laboratory workers in a community hospital

From May to September 1988, eight employees of a microbiology laboratory developed acute brucellosis (attack rate, 31%). Seven of the eight affected employees had clinical illness ranging from a nonspecific, flulike illness to severe hepatitis. Blood cultures obtained from five of the affected employees (63%) were positive for Brucella melitensis, biotype 3. Comparison of cases and controls showed that there were no risk factors besides employment in the laboratory. Based on work locations, assignments, and interviews, it was found that person-to-person, droplet, food-borne, and waterborne spread were unlikely. Our investigation disclosed that 6 weeks before the outbreak began, a frozen brucella isolate from a patient hospitalized 3 years earlier had been thawed and subcultured without the use of a biologic safety cabinet. This clinical isolate was subsequently identified as B. melitensis, biotype 3, identical to the employee isolates. It is presumed that transmission occurred via the airborne route. This outbreak reemphasized that all work on Brucella species, an established biosafety level 3 organism, must be conducted under a biologic safety hood. Furthermore, it might be prudent to perform all clinical "setups" under a safety hood since aerosolization commonly occurs during the initial processing of specimens and the majority of these specimens are from patients with uncertain diagnoses.