A nation-wide epidemiological study of acute bovine respiratory disease in France.

Acute bovine respiratory disease (ABRD) is a respiratory syndrome caused by various infectious agents, and represents a major economic and health problem in cattle herds worldwide. The aim of the study was to present how we can describe the epidemiological characteristics of ABRD in France, including risk factor analysis and spatio-temporal pattern investigation. The data were collected by specialized surveyors during the 2001 animal survey conducted by the French Ministry for Agriculture and Fisheries, from a representative sample of cattle herds. The health questionnaire concerned farm characteristics, practice of BRD vaccination, presence of ABRD, time of occurrence and number of affected animals for the period November 2000-October 2001. After a descriptive analysis of the syndrome, a space-time scan statistic was performed to detect potential clusters, and a logistic regression model was used for analysis of risk factors. The study sample included 16,581 cattle herds as representative of the 260,000 French herds. The ABRD cumulative incidence at farm level was 9.8%, the cumulative incidence at animal level was 2.1%, the cumulative mortality 0.1% and the lethality proportion 6.5%. ABRD occurred mainly during cold months with an epidemic peak in December. Spatial repartition of the syndrome showed that the whole territory was affected, with a higher number of cases in the north-east region, the main bovine production area in France. Three space-time clusters were identified in the period November 2000-February 2001. ABRD was significantly associated with production type, herd size, and BRD vaccination. Beef herds were less affected than dairy herds, and increased herd size increased the risk of ABRD. The outbreak was clustered in space and time, suggesting a common infectious agent for the epidemic in the detected areas. The influence of production type and herd size on syndrome occurrence highlighted the importance of management practices, human movement and animal density.