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Volume 24, Number 2—February 2018
Dispatch

Clusters of Human Infection and Human-to-Human Transmission of Avian Influenza A(H7N9) Virus, 2013–2017

Lei Zhou1, Enfu Chen1, Changjun Bao1, Nijuan Xiang1, Jiabing Wu, Shengen Wu, Jian Shi, Xianjun Wang, Yaxu Zheng, Yi Zhang, Ruiqi Ren, Carolyn M. Greene, Fiona Havers, A. Danielle Iuliano, Ying Song, Chao Li, Tao Chen, Yali Wang, Dan Li, Daxin Ni, Yanping Zhang, Zijian Feng, Timothy M. Uyeki, and Qun LiComments to Author 
Author affiliations: Public Health Emergency Center of the Chinese Center for Disease Control and Prevention, Beijing, China (L. Zhou, N. Xiang, R. Ren, Y. Wang, D. Li, D. Ni, Y. Zhang, Z. Feng, Q. Li); Zhejiang Center for Disease Control and Prevention, Hangzhou, China (E. Chen); Jiangsu Center for Disease Control and Prevention, Nanjing, China (C. Bao); Anhui Center for Disease Control and Prevention, Hefei, China (J. Wu); Fujian Center for Disease Control and Prevention, Fuzhou, China (S. Wu); Hebei Center for Disease Control and Prevention, Shijiazhuang, China (J. Shi); Shandong Center for Disease Control and Prevention, Jinan, China (X. Wang); Shanghai Center for Disease Control and Prevention, Shanghai, China (Y. Zheng); Shaanxi Center for Disease Control and Prevention, Xi’an, China (Y. Zhang); US Centers for Disease Control and Prevention, Atlanta, Georgia, USA (C.M. Greene, F. Havers, A.D. Iuliano, Y. Song, T.M. Uyeki); National Influenza Center of the Chinese Center for Disease Control and Prevention, Beijing (T. Chen); Chinese Center for Disease Control and Prevention, Beijing (Z. Feng)

Main Article

Table

Features of sporadic and clusters of human infections with avian influenza A(H7N9) virus, mainland China, February 1, 2013–June 30, 2017*

Category Total Epidemic†
First Second Third Fourth Fifth
Overall infections
Infections, no. 1,524 134 304 219 118 749
Deaths, no. (%)
 599 (39.3)
 44 (32.8)
 126 (41.4)
 99 (45.2)
 47 (39.8)
 283 (37.8)
Sporadic infections‡
Infections, no. 1,440 126 281 207 106 720
Deaths, no. (%)
 570 (39.6)
 39 (31.0)
 120 (42.7)
 94 (45.4)
 45 (42.5)
 272 (37.8)
Cluster infections
Infections, no. (%) 84 (5.5) 8 (6.0) 23 (7.6) 12 (5.5) 12 (10.2) 29 (3.9)
Deaths, no. (%)
 29 (34.5)
 5 (62.5)
 6 (26.1)
 5 (41.7)
 2 (16.7)
 11 (37.9)
All clusters
Clusters, no. 40 4 11 6 5 14
Clusters with 2 infections, no. 36 4 10 6 3 13
Clusters with 3 infections, no. 4 0 1 0 2 1
Deaths of index case-patients, no. (%) 19 (46.3) 3 (75.0) 5 (45.5) 2 (33.3) 1 (16.7) 8 (57.1)
Deaths of secondary case-patients, no. (%)
 10 (23.3)
 2 (50.0)
 1 (8.3)
 3 (50.0)
 1 (16.7)
 3 (20.0)
Clusters with probable human-to-human transmission only
Clusters, no. (%) 11 (30.0) 2 (50.0) 3 (27.3) 2 (33.3) 1 (20.0) 3 (21.4)
Clusters with 2 infections, no. 11 2 3 2 1 3
Clusters with 3 infections, no. 0 0 0 0 0 0
Infections, no. 22 4 6 4 2 6
Index, no. 11 2 3 2 1 3
Secondary, no. 11 2 3 2 1 3
Blood-related family members 12 4 2 2 2 2
Unrelated persons 10 0 4 2 0 4
Overall deaths, no. (%) 12 (54.5) 3 (75.0) 3 (50.0) 2 (50.0) 1 (50.0) 3 (50.0)
Of index case-patients, no. (%) 9 (81.8) 2 (100.0) 2 (66.7) 1 (50.0) 1 (100.0) 3 (100.0)
Of secondary case-patients, no. (%) 3 (27.3) 1 (50.0) 1 (33.3) 1 (50.0) 0 0

*Categorical variables among the 5 epidemics were compared by using χ2 or Fisher exact tests. Median age was compared by Wilcoxon test. The proportion of infections in clusters was lowest for the fifth epidemic; the proportion of infections in clusters per epidemic differed significantly during 2013–2017 (χ2 = 11.30; p = 0.023). The remaining items did not differ significantly among the 5 epidemics. The reporting of deaths may be delayed; therefore, these numbers may change as additional deaths are confirmed.
†The first epidemic was defined as February through August 31, 2013; each subsequent epidemic was defined as September 1 through August 31 of the following year.
‡Excludes human infections that were identified in clusters.

Main Article

1These authors contributed equally to this article.

Page created: January 17, 2018
Page updated: January 17, 2018
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