Analysis of an Epidemic Outbreak of Brucellosis in Slaughterhouse Workers

Abstract

Background: The appearance of an exceptional number of cases of Brucellosis at the end of 1996 in workers at a slaughterhouse led us to suspect an epidemic outbreak among this group. This study shows the methodology followed in the analysis of this outbreak as well as the results obtained. Methods: 1.- Epidemiological description of the outbreak: number of animals with brucellosis slaughtered, collection of information from different sources on the number of those affected: from the mutual insurance company, the record of working days lost, an epidemiological monitoring system and a survey amongst the workers. 2.- A case and control study was designed in order to determine, firstly, non-occupational risks - ingestion of fresh cheese or milk and care of animals - and secondly, occupational risks, depending on the job normally undertaken. 3.- To verify this a retrospective cohort study was designed. The exposed group was made up by workers in the slaughter area and the unexposed group comprised the remainder; any worker giving a positive result to the Rose of Bengal test and IgM brucellosis antibodies in serum was considered as a case Results: The description of the outbreak enabled us to establish that the cases occurred at the moment when most animals were slaughtered. tbat only occupational risks were relevar& that there were more symptomatic cases than notitied ones, and that the slaughter line operatols showed higher rates of attack than the remainder of the workers. Conclusions: This study analyses the possible causal relationship between analyzed exposure and the appearance of cases of bnwellosis in workers - a fact which backs the existing scientific evidente on the importance of the respiratory tract as a mechanism of transmission of this disease in the workplace.