A windy day in a sheep saleyard: an outbreak of Q fever in rural South Australia

Abstract

In December 2004, the Department of Human Services investigated an outbreak of Q fever in South Australia. A case-control study tested an association between attending a local saleyard and human illness. A case was defined as a person with clinical illness and evidence of seroconversion or high phase II IgM. Controls were selected from a database of community controls matched on sex, age group and postcode. Matched analysis of the first 15 cases with 45 controls indicated that contracting Q fever was associated with attending the saleyard on one particular day (adjusted odds ratio 15·3, 95% confidence interval 1·7-undefined, P = 0·014). Saleyard conditions were windy and conducive for airborne dispersal of contaminated particles. In total, 25 cases were detected. Of these, 22 cases had attended a local saleyard on the same day. This outbreak suggests cases were probably infected by a single exposure at a saleyard from infected sheep and dust. The investigation resulted in an increase in the local uptake of Q fever vaccination and extension of the Australian national vaccination programme.

Fig. 1.

Cases of Q fever by year and week of onset of symptoms, January 2004–February 2005, South Australia.

Fig. 2.

Cases of Q fever by week of onset of symptoms and attendance at saleyard, November 2004–January 2005, South Australia.