A cluster of 5 Congo Crimean Hemorrhagic Fever (CCHF) cases in Makkah slaughterhouse workers provided an opportunity to assess how exposure was occurring, the intensity of transmission, and evidence for mild and unapparent infections. We interviewed 122 of 126 total employees from 3 Makkah slaughterhouses about work history, work practices and recent illness. We obtained a serum specimen from each worker and tested them by indirect immunofluorescence (IFA) for CCHF antibodies. Including 4 surviving hospitalized cases, 13% of workers had antibody to CCHF. Excluding the hospitalized cases only two had antibody titers suggesting recent infection and 14.3% of workers reporting a recent illness with fever were seropositive compared to 9.3% of asymptomatic workers. Seropositive workers had worked in Saudi Arabian slaughterhouses for a mean of 5.12 years compared to 3.29 years for seronegatives (p<.01, Kruskal-Wallis test). Workers not exposed to animal blood or tissue were not seropositive compared to 15% of exposed workers (p=.12, Fisher exact test). No single work exposures or practices were associated with seropositivity. Long term exposure has probably led to seropositivity to CCHF in these workers. Asymptomatic infection or mild disease probably occurred but in minimal amounts.
Conclusion: