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How to interpret the transmissibility of novel influenza A(H7N9): an analysis of initial epidemiological data of human cases from China

Hiroshi Nishiura12*, Kenji Mizumoto13 and Keisuke Ejima14

Author Affiliations

1 School of Public Health, The University of Hong Kong, Level 6, Core F, Cyberport 3, Pokfulam, Hong Kong

2 Department of Global Health Policy, Graduate School of Medicine, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 110-0033, Japan

3 Institute of Tropical Medicine and the Global Center of Excellence Program, Nagasaki University, Nagasaki, Japan

4 Department of Mathematical Informatics, Graduate School of Information Science and Technology, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan

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Theoretical Biology and Medical Modelling 2013, 10:30  doi:10.1186/1742-4682-10-30

Published: 4 May 2013

Abstract

Background

As the human infections with novel influenza A(H7N9) virus have been reported from several different provinces in China, the pandemic potential of the virus has been questioned. The presence of human-to-human transmission has not been demonstrated, but the absence of demonstration does not guarantee that there is no such transmission.

Methods

A mathematical model of cluster size distribution is devised without imposing an assumption of subcriticality of the reproduction number and accounting for right censoring of new clusters. The proportion of cases with a history of bird contact is analytically derived, permitting us to fit the model to the observed data of confirmed cases. Using contact history with bird among confirmed cases (nā€‰=ā€‰129), we estimate the reproduction number of the novel influenza A(H7N9) from human to human.

Results

Analysing twenty confirmed cases with known exposure, the reproduction number for human-to-human transmission was estimated at 0.28 (95% CI: 0.11, 0.45). Sensitivity analysis indicated that the reproduction number is substantially below unity.

Conclusions

It is unlikely to observe an immediate pandemic of novel influenza A(H7N9) virus with human to human transmission. Continued monitoring of cases and animals would be the key to elucidate additional epidemiological characteristics of the virus.