Are Visitor and Personnel Downtime Restrictions an Effective Biosecurity Measure to Prevent the Indirect Transmission of Pathogens to Livestock?

Abstract

Downtime, also known as an animal avoidance period, refers to a 24–72 h period during which individuals who have had contact with one animal species avoid subsequent contact with other susceptible species. This scoping review critically evaluated the effectiveness of downtime as a biosecurity measure. Peer-reviewed studies were identified and analysed using three electronic databases (Pubmed, Web of Science and Scopus). Two experimental studies directly evaluated downtime, nine additional articles examined human nasal carriage of pathogens after exposure to infected animals and seven articles evaluated the effectiveness of hygiene-based biosecurity measures targeting indirect mechanical pathogen transmission via humans (n = 14 unique articles in total; topical overlap noted where studies contributed to multiple categories). No evidence indicated an added benefit of downtime over other, more evidence-based measures such as hand hygiene, changing of clothes and boots and showering. While certain studies were able to identify the nasal carriage of pathogens, only one study indicated possible consequent transmission to naïve animals. This limited and species-specific evidence base reveals a critical gap between policy recommendations and scientific support for downtime. Based on these results, no clear benefit or necessity of downtime over other measures have been identified, other than its ability to deter unnecessary visitors, but these do not outweigh the impracticalities associated with an ‘animal avoidance period’. Resources and policy efforts should therefore shift from enforcing downtime toward ensuring and verifying adherence to fundamental hygiene measures.