Comparison of the three waves of avian influenza A(H7N9) virus circulation since live poultry markets were permanently closed in the main urban areas in Zhejiang Province July, 2014~June, 2017

Summary

Background

The sudden increase of the number of human cases infected with avian influenza A(H7N9) virus after September, 2016 raised global concern.

Objectives

To assess the changes of epidemiological characteristics of H7N9 cases since the massive closure of live poultry markets (LPMs)in the main urban areas in Zhejiang province.

Methods

We used descriptive statistics to compare epidemiological characteristics of the three distinct waves of H7N9 cases in Zhejiang province. The rural or urban cases were defined according to the location where the patients had exposure within two weeks before illness onset.

Results

Between July, 2014 and June, 2017, 166 H7N9 cases were reported in Zhejiang province, with 45, 34 and 87 cases reported in the third, fourth and fifth wave respectively. Across the three waves, most reported cases were from rural areas. A similar percentage of cases in all three waves reported exposure to LPMs, raising poultry at home or around the house, as well as occupational exposure. Compared to the third (80.00%) and fourth wave (70.59%), a significantly larger proportion of cases from the non-LPMs closure areas were observed in the fifth wave(89.66%) (p=0.034).

Conclusion

Epidemiological characteristics of human cases infected with avian influenza A(H7N9) virus had generally remained unchanged since the massive closure of LPMs in the main urban area of Zhejiang province. The sudden increase of the number of H7N9 cases in the fifth wave were mainly attributed to the excessive cases reported from areas where LPMs were not permanently closed.