Designing a Syndromic Bovine Mortality Surveillance System: Lessons Learned From the 1-Year Test of the French OMAR Alert Tool

Between May 2018 and May 2019, a syndromic bovine mortality surveillance system (OMAR) was tested in 10 volunteer French departements (French intermediate-level administrative unit) to assess its performance in real conditions, as well as the human and financial resources needed to ensure normal functioning. The system is based on the automated weekly analysis of the number of cattle deaths reported by renderers in the Fallen Stock Data Interchange Database (FSDI) established in January 2011. In our system, every Thursday, the number of deaths is grouped by ISO week and small surveillance areas and then analyzed using traditional time-series analysis steps (cleaning, prediction, signal detection). For each of the five detection algorithms implemented (i.e., the exponentially weighted moving average chart, cumulative sum chart, Shewhart chart, Holt-Winters and historical limits algorithms), seven detection limits are applied, giving a signal score from 1 (low excess mortality) to 7 (high excess mortality). The severity of excess mortality (alarm) is then classified into four categories, from very low to very high, by combining the signal scores, the relative excess mortality, and the persistence of the signal(s) over the previous four weeks. Detailed and interactive weekly reports and a short online questionnaire help pilot departements and the OMAR central coordination cell assess the performance of the system. During the one-year test, the system showed highly variable sensitivity among departements. This variability was partly due to the demographic distribution of cattle (very few signals in low-density areas), but also to the renderer’s delay in reporting to the FSDI (on average only 40% of the number of real deaths had been transmitted within week, with huge variations among departements). As a result, in the pilot departements, very few alarms required on-farm investigation and excess mortality often involved a small number of farms already known to have health or welfare problems. Despite its perfectibility, the system nevertheless proved useful in the daily work of animal health professionals for collective as well as individual surveillance. The test is still ongoing for a second year in nine departements to evaluate the effectiveness of the improvements agreed upon at the final meeting.