Q fever. A call to heighten our index of suspicion.

The prevalence of Q fever infection is probably underestimated. In Michigan, the first two reported human cases of Q fever occurred in 1984. The case-patients lived in adjacent, rural counties and had multiple exposures to goats. We conducted a serosurvey of goat owners and a reference population to compare the prevalence of Q fever antibodies in the two-county area. Goat owners were almost three times more likely to be seropositive with Q fever antibodies than the reference population (43% vs 15%). Among goat owners, individual and household seropositivity prevalences were positively correlated with the number of goats, the number of positive goats, and the number of goat births on the farm. Q fever should be considered more often in the differential diagnosis of patients with compatible illness, especially those with frequent animal contact.