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Volume 18, Number 8—August 2012

Dispatch

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 Peiris2Comments to Author 
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)

Main Article

Table

Poisson generalized linear models for influenza virus (H9N2) isolation rates in live poultry markets, by poultry type, Hong Kong, September 1999–May 2011*

Variable Chickens
Minor poultry
aRR (95% CI) p value aRR (95% CI) p value
Period

No rest day

1.69 (0.91–3.15) 0.10 2.47 (1.23–4.98) 0.01

1 rest day with quail†

1.25 (0.73–2.15) 0.42 0.99 (0.49–2.01) 0.97

1 rest day without quail†

1.00 (0.60–1.64) 0.97 0.99 (0.53–1.85) 0.97

2 rest days

Reference Reference

Ban on keeping live poultry overnight in live poultry markets

0.16 (0.04–0.60) 0.006 0.01‡
Proportion of chickens imported, per 10% increase 0.87 (0.73–1.02) 0.09 1.02 (0.79–1.32) 0.87
Total sales

Chickens, per 100,000 sold

1.04 (0.98–1.09) 0.19 1.05 (0.98–1.13) 0.15

Minor poultry, per 100,000 sold

2.52 (1.49–4.25) 0.001 3.15 (1.54–6.44) 0.002

Chicken × minor poultry§

0.98 (0.97–1.00) 0.03 0.97 (0.95–0.99) 0.007
Ventilation system

Natural ventilation

Reference Reference

Market economic air treatment system

1.02 (0.79–1.31) 0.89 1.02 (0.78–1.34) 0.87

Air conditioned

0.71 (0.42–1.22) 0.21 0.97 (0.56–1.68) 0.90
Temperature, °C 0.98 (0.99–1.02) 0.96 1.05 (0.96–1.16) 0.29
Relative humidity, % 1.00 (0.99–1.02) 0.63 0.99 (0.97–1.00) 0.10
Seasonality term¶

α (cosine component)

0.19 (–0.19 to 0.58) 0.33 –0.10 (–0.57 to 0.37) 0.68

β (sine component)

0.30 (–0.11 to 0.70) 0.15 0.47 (–0.06 to 0.99) 0.08

*aRR, adjusted relative risk.
†Indicates before and after ban on sales of live quail.
‡Reliable confidence interval cannot be estimated because of zero isolation of influenza virus (H9N2) from minor poultry after introduction of a ban on keeping live poultry overnight in live poultry markets. p value was calculated using likelihood ratio test.
§Interaction term.
¶The seasonality coefficients α and β contribute to the estimated isolation rate in week t via the terms αcos(2πt/52) + βsin(2πt/52).

Main Article

1These authors are joint first authors.

2These authors are joint senior authors.

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