A large outbreak of Q fever in the West Midlands: windborne spread into a metropolitan area?

The largest outbreak of the zoonotic disease Q fever recorded in the United Kingdom (UK) occurred in Birmingham in 1989. One hundred and forty-seven cases were identified, 125 of whom were males, and 130 of whom were between 16 and 64 years of age. Fewer cases of Asian ethnic origin were observed than expected (p < 0.01), and more smokers (p < 0.005). A case control study (26 cases and 52 matched controls) produced no evidence that direct contact with animals or animal products had caused the outbreak. The epidemic curve suggested a point source exposure in the week beginning 10 April. The home addresses of cases were clustered in a rectangle 11 miles (18.3 km) north/south by 4 miles (6.7 km) east/ west, and attack rates became lower towards the north. Directly south of this area were farms engaged in outdoor lambing and calving, a potent source of coxiella spores. A retrospective computerised analysis showed that the geographical distribution of cases was associated with a source in this area (p < 0.00001). On 11 April, unusual southerly gales of up to 78 mph (130 km/h) were recorded. The probable cause of the outbreak was windborne spread of coxiella spores from farmland to the conurbation.