Assessing the role of contact tracing in a suspected H7N2 influenza A outbreak in humans in Wales

Abstract

BackgroundThe detailed analysis of an outbreak database has been undertaken to examine the role of contact tracing in controlling an outbreak of possible avian influenza in humans. The outbreak, initiating from the purchase of infected domestic poultry, occurred in North Wales during May and June 2007. During this outbreak, extensive contact tracing was carried out. Following contact tracing, cases and contacts believed to be at risk of infection were given treatment/prophylaxis.MethodsWe analyse the database of cases and their contacts identified for the purposes of contact tracing in relation to both the contact tracing burden and effectiveness. We investigate the distribution of numbers of contacts identified, and use network structure to explore the speed with which treatment/prophylaxis was made available and to estimate the risk of transmission in different settings.ResultsFourteen cases of suspected H7N2 influenza A in humans were associated with a confirmed outbreak among poultry in May-June 2007. The contact tracing dataset consisted of 254 individuals (cases and contacts, of both poultry and humans) who were linked through a network of social contacts. Of these, 102 individuals were given treatment or prophylaxis. Considerable differences between individuals' contact patterns were observed. Home and workplace encounters were more likely to result in transmission than encounters in other settings. After an initial delay, while the outbreak proceeded undetected, contact tracing rapidly caught up with the cases and was effective in reducing the time between onset of symptoms and treatment/prophylaxis.ConclusionsContact tracing was used to link together the individuals involved in this outbreak in a social network, allowing the identification of the most likely paths of transmission and the risks of different types of interactions to be assessed. The outbreak highlights the substantial time and cost involved in contact tracing, even for an outbreak affecting few individuals. However, when sufficient resources are available, contact tracing enables cases to be identified before they result in further transmission and thus possibly assists in preventing an outbreak of a novel virus.

Oseltamivir Inhibits H7 Influenza Virus Replication in Mice Inoculated by the Ocular Route

“…However, unlike other influenza virus subtypes that cause predominant respiratory disease in humans, H7 influenza viruses frequently result in ocular rather than respiratory symptoms (3). Oseltamivir prophylaxis has nonetheless been prescribed during several H7 virus outbreaks resulting in human infection, including H7N7 virus in The Netherlands in 2003, H7N3 virus in Canada in 2004, and H7N2 in Wales in 2007 (9,16,25) (Table 1). Retrospective studies have examined the role of oseltamivir prophylaxis in developing conjunctivitis and/or influenza-like illness following H7 virus exposure, finding that the prophylactic use of oseltamivir resulted in a decreased risk of virus infection, including self-reported conjunctivitis (16,17,20,22).…”

The Matrix Gene Segment Destabilizes the Acid and Thermal Stability of the Hemagglutinin of Pandemic Live Attenuated Influenza Virus Vaccines

“…Within the past 2 decades, the cross-species transmission of a number of avian influenza viruses of low (H9N2, H7N2, H7N3, and H7N7) and high (H5N1, H7N3, and H7N7) pathogenicity into humans has caused infections of varying severity (5)(6)(7)(8)(9)(10). This list now includes the recently emerged H7N9 influenza A virus outbreak in China (11).…”

Mammalian Models for the Study of H7 Virus Pathogenesis and Transmission

“…1) (2007; Nguyen-Van-Tam et al 2006; Puzelli et al 2005). Suspected and confirmed human cases have been reported following several of these outbreaks, with disease ranging from mild to severe (Dudley 2008; Eames et al 2010; Nguyen-Van-Tam et al 2006; Puzelli et al 2005). …”