Predicting prolonged bovine tuberculosis breakdowns in Great Britain as an aid to control

Bovine tuberculosis (bTB) is an important notifiable disease in cattle in Great Britain (GB), and is subject to statutory control measures. Despite this, disease incidence has increased since the mid-1980s, and around 30% of herd breakdowns continue for more than 240 days. This is twice the shortest possible time for confirmed breakdowns to test clear from infection (≈120 days), and four times the shortest possible time for unconfirmed breakdowns (≈60 days). These "prolonged" breakdowns consume substantial resources and may act as an ongoing source of infection. It is not clear why some breakdowns become prolonged. Existing detailed case-control data have been re-analysed to determine risk factors for breakdowns lasting longer than 240 days, the strongest of which was the confirmation status of the breakdown: OR 12.6 (95%CI: 6.7-25.4). A further model restricted to data available early on in a breakdown for all breakdowns nationally, can predict 82-84% of prolonged breakdowns with a positive predictive value of 44-49% when validated using existing national datasets over a 4-year period. Identification of prolonged breakdowns at an earlier stage could help to target bTB controls in GB.