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Clin Infect Dis. 2015 May 4. pii: civ345. [Epub ahead of print]
Differences in the epidemiology of human cases of avian influenza A(H7N9) and A(H5N1) viruses infection.
Qin Y1, Horby PW2, Tsang TK3, Chen E4, Gao L5, Ou J6, Nguyen TH7, Duong TN7, Gasimov V8, Feng L1, Wu P3, Jiang H1, Ren X1, Peng Z1, Li S1, Li M1, Zheng J1, Liu S4, Hu S5, Hong R6, Farrar JJ9, Leung GM3, Gao GF10, Cowling BJ3, Yu H1.
Author information
Abstract
BACKROUND:
The pandemic potential of avian influenza viruses A(H5N1) and A(H7N9) remains an unresolved but critically important question.
METHODS:
We compared the characteristics of sporadic and clustered cases of human H5N1 and H7N9 infection, estimated the relative risk of infection in blood-related contacts, and the reproduction number (R).
RESULTS:
We assembled and analyzed data on 720 H5N1 cases and 460 H7N9 cases up to November 02 2014. The severity and average age of sporadic/index cases of H7N9 was greater than secondary cases (71% requiring ICU admission versus 33%, p=0?007; median age 59 years versus 31, p<0?001). We observed no significant differences in the age and severity between sporadic/index and secondary H5N1 cases. The upper limit of the 95% CI for reproduction number (R) was 0?12 for H5N1 and 0?27 for H7N9. A higher proportion of H5N1 infections occurred in clusters (20%) compared to H7N9 (8%). The relative risk of infection in blood-related contacts of cases compared to unrelated contacts was 8.96 for H5N1 (95% CI 1.30, 61.86) and 0.80 for H7N9 (95% CI 0.32, 1.97).
CONCLUSIONS:
The results are consistent with an ascertainment bias towards severe and older cases for sporadic H7N9 but not for H5N1. The lack of evidence for ascertainment bias in sporadic H5N1 cases, the more pronounced clustering of cases, and the higher risk of infection in blood-related contacts, support the hypothesis that susceptibility to H5N1 may be limited and familial. This analysis suggests the potential pandemic risk may be greater for H7N9 than H5N1.
? The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.
PMID: 25940354 [PubMed - as supplied by publisher]
Differences in the epidemiology of human cases of avian influenza A(H7N9) and A(H5N1) viruses infection.
Qin Y1, Horby PW2, Tsang TK3, Chen E4, Gao L5, Ou J6, Nguyen TH7, Duong TN7, Gasimov V8, Feng L1, Wu P3, Jiang H1, Ren X1, Peng Z1, Li S1, Li M1, Zheng J1, Liu S4, Hu S5, Hong R6, Farrar JJ9, Leung GM3, Gao GF10, Cowling BJ3, Yu H1.
Author information
Abstract
BACKROUND:
The pandemic potential of avian influenza viruses A(H5N1) and A(H7N9) remains an unresolved but critically important question.
METHODS:
We compared the characteristics of sporadic and clustered cases of human H5N1 and H7N9 infection, estimated the relative risk of infection in blood-related contacts, and the reproduction number (R).
RESULTS:
We assembled and analyzed data on 720 H5N1 cases and 460 H7N9 cases up to November 02 2014. The severity and average age of sporadic/index cases of H7N9 was greater than secondary cases (71% requiring ICU admission versus 33%, p=0?007; median age 59 years versus 31, p<0?001). We observed no significant differences in the age and severity between sporadic/index and secondary H5N1 cases. The upper limit of the 95% CI for reproduction number (R) was 0?12 for H5N1 and 0?27 for H7N9. A higher proportion of H5N1 infections occurred in clusters (20%) compared to H7N9 (8%). The relative risk of infection in blood-related contacts of cases compared to unrelated contacts was 8.96 for H5N1 (95% CI 1.30, 61.86) and 0.80 for H7N9 (95% CI 0.32, 1.97).
CONCLUSIONS:
The results are consistent with an ascertainment bias towards severe and older cases for sporadic H7N9 but not for H5N1. The lack of evidence for ascertainment bias in sporadic H5N1 cases, the more pronounced clustering of cases, and the higher risk of infection in blood-related contacts, support the hypothesis that susceptibility to H5N1 may be limited and familial. This analysis suggests the potential pandemic risk may be greater for H7N9 than H5N1.
? The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.
PMID: 25940354 [PubMed - as supplied by publisher]