Respiratory Illness in a Piggery Associated with the First Identified Outbreak of Swine Influenza in Australia: Assessing the Risk to Human Health and Zoonotic Potential

Abstract

Australia was previously believed to be free of enzootic swine influenza viruses due strict quarantine practices and use of biosecure breeding facilities. The first proven Australian outbreak of swine influenza occurred in Western Australian in 2012, revealing an unrecognized zoonotic risk, and a potential future pandemic threat. A public health investigation was undertaken to determine whether zoonotic infections had occurred and to reduce the risk of further transmission between humans and swine. A program of monitoring, testing, treatment, and vaccination was commenced, and a serosurvey of workers was also undertaken. No acute infections with the swine influenza viruses were detected. Serosurvey results were difficult to interpret due to previous influenza infections and past and current vaccinations. However, several workers had elevated haemagglutination inhibition (HI) antibody levels to the swine influenza viruses that could not be attributed to vaccination or infection with contemporaneous seasonal influenza A viruses. However, we lacked a suitable control population, so this was inconclusive. The experience was valuable in developing better protocols for managing outbreaks at the human-animal interface. Strict adherence to biosecurity practices, and ongoing monitoring of swine and their human contacts is important to mitigate pandemic risk. Strain specific serological assays would greatly assist in identifying zoonotic transmission.

Keywords: Australia; human; influenza; pandemic; swine.

Figure 1

Date of onset of influenza-like illness and respiratory virus detections in 23 workers at a piggery in WA preceding and during an outbreak of respiratory tract illness and deaths in swine. The red columns are those with respiratory illness without laboratory confirmation either because they were not tested (17 workers) or because the results were negative or inconclusive. The blue column is confirmed seasonal A(H3N2) and the green are confirmed RV infections. Initial serologic testing at the DAFWA had suggested influenza infection and on 4 August 2012, a site visit was made by officers from the CDCD and the DAFWA.