Isolation rates of Brucella melitensis in an endemic area and implications for laboratory safety

A retrospective study was conducted to assess the potential threat posed by processing blood cultures to clinical microbiology laboratory personnel working in an area endemic for Brucella melitensis in southern Israel. The computerized laboratory records for the 2002-2009 period were reviewed, and the proportion of aerobic vials from which Brucella organisms were isolated out of the total number of positive aerobic blood culture vials was determined. During the 8-year period, B. melitensis was isolated in 514 of 20,620 (2.5%) positive vials. Isolation rate increased at the end of the period reaching a peak of 5.3% in 2008. Between April 2008 and September 2009, the proportion of aerobic blood cultures from which B. melitensis was isolated was even higher than that positive for pneumococci (4.3% and 2.6%, respectively, P < 0.001). Although it has been recommended that processing of Brucella cultures should be confined to a Class II biologic safety cabinet, by the time the organism is identified, extensive manipulation of culture media has already been performed and inadvertent exposure of laboratory personnel may have already occurred. To reduce the risk of transmission, all positive blood culture vials in endemic areas should be processed in a safety cabinet.