Background: The aim of this study was to describe an outbreak of acute fever in a rural town from Soria (Spain) in the spring of 1998 and to know the prevalence of IgG antibodies to Coxiella burnetii in this population.
Methods: 1. Outbreak of Q fever: epidemiological, clinical and analytical data were obtained by standardised questionnaire and the clinical records from all clinical cases. These cases were confirmed by complement fixation test.2. Seroprevalence: 253 sera were chosen by not probabilistic sampling of convenience of sera samples collected between 1 September 1996 and 28 February 1999. Were regarded as positive anti-phase II C. burnetii IgG titles by indirect inmunoflourescence assay equal or higher to 1/80.
Results: 1. A total of 14 cases of Q fever with a mean age of 21.5 +/-3.1 years were confirmed. 64% presented pneumonia and in 36% the symptoms were nonspecific. No patient had direct contact with animals but near to the town there were 4 flocks with 2,614 sheeps overall. 2. The seroprevalence was 60% (95% confidence interval: 54-66). The seroprevalence was not increased with the outbreak (p > 0.05).
Conclusion: The high prevalence of antibodies to C. burnetii in this population shows that this area is hyperendemic for such infection, but generally is asymptomatic or clinical signs are extremely mild because no cases of Q fever had been reported in the years before. Probably indirect exposure to flocks of sheep was the source of infection and transmission mechanism airborne.