Infectious Diseases 2017

Infectious Diseases 2017

H7N9: human infection and human-to-human transmission, 2013–2017

Emerg Infect Dis Vol 24, Num 2 - Feb 2018 22 November, 2017

Since December 2016, the number of human infections with avian influenza A(H7N9) virus in China has increased markedly, prompting concerns of pandemic influenza. Early signals of greater human-to-human transmissibility might be increased number and size of clusters of epidemiologically linked human infections and clusters of case-patients who are not blood relatives or increased numbers of case-patients with mild illness. To elucidate whether the increase in humans infections during the fifth epidemic (2016–2017) in China was associated with increased human-to-human transmissibility of A(H7N9) virus, a group of researchers compared the characteristics of clusters of A(H7N9) case-patients during the fifth epidemic with those of clusters of case-patients identified from the previous 4 epidemics (2013–2016).
Despite the surge in human infections with A(H7N9) virus during the fifth epidemic in China, the similarity in numbers and sizes of clusters and proportions of clusters with probable human-to-human transmission during 2013–2017 suggest no change in human-to-human A(H7N9) virus transmission risk over time. These findings suggest that the increase in human infections during the fifth epidemic probably reflects an increase in sporadic poultry-to-human A(H7N9) virus transmission over a wide geographic area in China.