Assessing the Mandatory Bovine Abortion Notification System in France Using Unilist Capture-Recapture Approach

Abstract

The mandatory bovine abortion notification system in France aims to detect as soon as possible any resurgence of bovine brucellosis. However, under-reporting seems to be a major limitation of this system. We used a unilist capture-recapture approach to assess the sensitivity, i.e. the proportion of farmers who reported at least one abortion among those who detected such events, and representativeness of the system during 2006–2011. We implemented a zero-inflated Poisson model to estimate the proportion of farmers who detected at least one abortion, and among them, the proportion of farmers not reporting. We also applied a hurdle model to evaluate the effect of factors influencing the notification process. We found that the overall surveillance sensitivity was about 34%, and was higher in beef than dairy cattle farms. The observed increase in the proportion of notifying farmers from 2007 to 2009 resulted from an increase in the surveillance sensitivity in 2007/2008 and an increase in the proportion of farmers who detected at least one abortion in 2008/2009. These patterns suggest a raise in farmers’ awareness in 2007/2008 when the Bluetongue Virus (BTV) was detected in France, followed by an increase in the number of abortions in 2008/2009 as BTV spread across the country. Our study indicated a lack of sensitivity of the mandatory bovine abortion notification system, raising concerns about the ability to detect brucellosis outbreaks early. With the increasing need to survey the zoonotic Rift Valley Fever and Q fever diseases that may also cause bovine abortions, our approach is of primary interest for animal health stakeholders to develop information programs to increase abortion notifications. Our framework combining hurdle and ZIP models may also be applied to estimate the completeness of other clinical surveillance systems.

Was the French clinical surveillance system of bovine brucellosis influenced by the occurrence and surveillance of other abortive diseases?

“…This study confirmed the influence of the production type and herd size on the probability for a farmer to report abortion (Bronner et al, 2013). Indeed, beef cattle farmers face difficulties in detecting and catching aborting females at pasture for a serological analysis (Bronner et al, 2014).…”

“…Besides, the proportion of notifying farmers (i.e. the ratio of the number of farmers who reported at least one abortion to the total number of farmers) and the sensitivity of the surveillance system were highly influenced by the occurrence of the bluetongue virus serotype 8 (BTV-8) in 2007/2008 in France, due to an increase in abortions occurrence and to an increase in farmers' and veterinarians' awareness of the need to detect the disease (Bronner et al, 2013). However, we wondered whether this influence was specific to BTV-8, or would also exist if other abortive diseases occurred or were monitored.…”

Estimating the incidence of equine viral arteritis and the sensitivity of its surveillance in the French breeding stock

“…In epidemiology, depending on the number of data sources, two capture-recapture approaches can be used: multilist and unilist approaches (Vergne et al, 2015). While multilist capture-recapture methods are relevant when infected units can be detected by several surveillance systems or components, unilist methods focus on the frequency of detection of infected units by a single source ("one list") of observations (Bronner et al, 2013;Chao et al, 2001;Del Rio Vilas and Böhning, 2008;Vergne et al, 2012). In this study, a unilist capture-recapture approach was used with the detection source being the surveillance component targeting the breeding stock.…”

Epidemiological surveillance methods for vector-borne diseases

“…Elbers et al (26) describe the early detection of the first BT virus 8-(BTV-8-) infected sheep flocks in the Netherlands by farmers and veterinary practitioners on the basis of an unusual clinical syndrome. Another use of syndromic surveillance is the potential for the notification of abortions in livestock to provide early warning of RVF (27). The use of a continuous indicator (milk yield) for early detection of VBDs, using a scan statistic to detect clusters of low milk production, has been evaluated and the main limitation was found to be its low specificity (28).…”