Avian Influenza and Ban on Overnight Poultry Storage in Live Poultry Markets, Hong Kong

Y.H. Connie Leung¹, Eric H.Y. Lau¹, Li Juan Zhang, Yi Guan², Benjamin J. Cowling², and J.S. Malik Peiris²

Author affiliations: Li Ka Shing Faculty of Medicine School of Public Health, The University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China (Y.H.C. Leung, E.H.Y. Lau, B.J. Cowling, J.S.M. Peiris); and State Key Laboratory of Emerging Infectious Diseases, The University of Hong Kong, Hong Kong (L.J. Zhang, Y. Guan)

Abstract

We analyzed ≈12 years of surveillance data on avian influenza in Hong Kong live poultry markets. A ban on keeping live poultry overnight in these markets reduced virus isolation rates by 84% in chickens (p = 0.006) and 100% (p = 0.01) in minor poultry.

Previous influenza pandemics originated from influenza viruses of birds (1). Live poultry markets play a crucial role in maintenance, amplification, and dissemination of avian influenza viruses (2,3) and are high-risk locations for potential zoonotic transmission of highly pathogenic avian influenza (HPAI) virus (H5N1) to humans (4,5). From September 1999 through May 2011, fecal dropping samples were collected monthly under the poultry cages in live poultry markets in Hong Kong as part of a systematic longitudinal avian influenza surveillance program. During the 12-year period of surveillance, several interventions were implemented by the Hong Kong government in response to outbreaks of influenza virus (H5N1) in live poultry markets and on poultry farms. In July 2001, a monthly rest day was first implemented; under this system, all poultry in live poultry markets must be sold or slaughtered at the end of the day, poultry stalls must be cleaned and disinfected, and the stalls must be left free of live poultry for 1 day before restocking any live poultry the next day. In February 2002, a ban on sales of live quail was implemented in because an influenza virus (H9N2) lineage commonly isolated from quail possessed the internal genes of the virus that caused the avian influenza (H5N1) outbreak in Hong Kong in 1997 (6). In response to further incursions of avian influenza (H5N1) into poultry markets and farms in Hong Kong, a second monthly rest day in live poultry markets was introduced in March 2003, and a complete ban on holding live poultry overnight in live poultry markets was implemented in July 2008.
Previously, we analyzed data from September 1999 through December 2005 and demonstrated that 1 rest day per month significantly reduced isolation rates of influenza virus in minor poultry (i.e., silkie chickens, pigeons, chukars, guinea fowls, and pheasants) but that an additional rest day each month did not significantly reduce the isolation rate further (7). In this follow-up study, which includes an additional 6 years of data, we investigated the effect of a ban on keeping live poultry overnight at live poultry markets on isolation rates of influenza A virus (H9N2) from chickens and minor poultry.