Seroprevalence of Brucella antibodies among vaccine manufacturing workers in contact with the Brucella melitensis Rev.1 vaccine strain

ABSTRACT Background Cattle vaccination remains an essential measure for the control of brucellosis. Strict preventive measures are applied to protect vaccine manufacturing workers (VMW) employed in processing these live attenuated vaccines. We analyzed the serological responses of VMW in contact with the Brucella melitensis Rev.1 strain. Methods We conducted an observational study of a cohort of VMW in a Spanish biopharmaceutical company, a leader in manufacturing veterinary products. The results of the Brucella serological tests carried out on these workers between 2012 and 2019 were reviewed, as well as demographic data, length of time in the company (seniority), and level of exposure. Multivariate analysis was performed with the logistic regression test. Results Of the 115 VMW studied, 47 (41%) showed positive Rose Bengal tests during company check-ups. Exposure levels were correlated with seropositivity, with an adjusted OR of 6.6 (95% CI: 2.1-20.3) for the high exposure and 2.0 (95% CI: 0.6-6.7) for the medium exposure groups. Sixteen (34%) seropositive VMW demonstrated an acute serologic pattern of IgG and IgM antibodies seropositivization, while 31 (66%) manifested a chronic serologic pattern of constant or intermittent positive IgG antibodies with persistently negative IgM antibodies. Seniority was inversely associated with the acute pattern: adjusted OR of 0.88 (95% CI: 0.79-0.97) for each year added. No seropositive VMW showed evidence of active brucellosis during follow up. Conclusion Despite strict safety measures, a percentage of VMW were exposed to the Rev.1 strain. Exposure levels were correlated with seropositivity. None of them developed symptomatic infection during follow-up. Two different serological patterns were observed: an acute IgM-positive pattern or a chronic IgM-negative pattern. Seniority was associated with the chronic pattern.