Clinical Q fever in Northern Ireland 1962-1989.

Q fever was diagnosed in 443 patients in Northern Ireland between 1962 and 1989. From 1986 onwards there was an increase, which peaked in 1989 with 107 cases of whom 47 were infected in Ballycastle, Co Antrim. There were three outbreaks and 21 clusters of patients with Q fever. Most cases were in April and May which correlated with the peak lambing and calving season. Q fever mainly affected males in the 40-49 year old age group. County Antrim had the highest prevalence rate of 40/100,000 population and also had the most sheep. The number of sheep in Northern Ireland has doubled in the past ten years. Q fever was strongly associated with occupation and animal contact. Eighty-seven patients (19.6%) drank unpasteurized milk. The commonest presenting illnesses were pneumonia (62.8%), influenza-like illness (24.6%), involvement of the heart (9.0%) and hepatitis (1.6%). Thirty-two patients (7.2%) had endocarditis, 20 of whom had prosthetic valves and three of whom died. Coxiella burnetii was present on valves removed from seven patients.