THE RISK OF ACQUIRING Q-FEVER ON FARMS - A SEROEPIDEMIOLOGICAL STUDY

Objectives-To determine the occupational risk of Q fever. Design-Cohor t study. Setting-Community: five English local authority districts. Su bjects and methods-Prevalence and incidence of immunoglobulin G (IgG) specific antibody to Coxiella burnetii phase II antigen was measured i n a representative (study) cohort of farm workers in the United Kingdo m, and detailed exposure data were collected. Also seroprevalence of Q fever in a (control) cohort of police and emergency service personnel was measured. Results-Prevalence was significantly (P < 0.01) higher in the study cohort (105/385 v 43/395). During the first 12 month peri od after enrolment no seroconversions were found (upper 95% confidence limit: 1318/100 000/year). During the second 12 month period after en rolment two seroconversions were found, equalling an incidence of 813/ 100 000/year (95% confidence interval (95% CI) 98-2937/100 000/year). No association was found between seroprevalence and age. In the study cohort, extent of total contact with farm animals seemed more importan t than exposure to any specific animal: full time employees were more than four times more likely to be antibody positive than part time emp loyees (P < 0.05). Exposure to cattle, but not sheep, goats, cats, raw milk, and hay (all reported sources of Q fever) was associated with b eing positive to Coxiella burnetii IgG by univariate analysis but this association was not independent of total farm animal contact. Conclus ions-The risk of Q fever on livestock farms is related to contact with the farm environment rather than any specific animal exposure. The ab sence of an increasing prevalence with age suggests that exposure may occur as clusters in space and time (outbreaks).