Limited human-to-human transmission of avian influenza A(H7N9) virus, Shanghai, China, March to April 2013

Abstract

In April 2013, two members of one family were successively confirmed as cases of avian influenza A(H7N9) virus infection in Shanghai, China. Respiratory specimens from the two cases and their close contacts were tested using real-time reverse-transcription (RT)-PCR. Paired serum specimens from contacts were tested by haemagglutination inhibition assay and microneutralisation test. The index patient developed severe pneumonia. Her husband presented with pneumonia shortly thereafter. Both cases had highly similar clinical features and infection with A(H7N9) virus was confirmed in both cases by genetic analysis. Phylogenetic analysis revealed a high level of similarity between the sequences from the two patients and environmental samples collected from wet markets in Minhang and Changning districts. Six samples from the Changning wet market were confirmed as A(H7N9) positive. Of 27 close contacts, one developed mild respiratory symptoms and another tested positive for A(H7N9) antibodies, but both were negative by real-time RT-PCR. The other 25 close contacts of both cases were A(H7N9) negative. Limited human-to-human transmission of the virus most likely occurred in the family cluster. However, other close contacts did not test positive for the virus, suggesting limited potential for extensive human-to-human transmission of the virus.

Clinical severity of human infections with avian influenza A(H7N9) virus, China, 2013/14

“…Control of the virus in animals is complicated, because the infections in poultry are asymptomatic [11]. Human-to-human transmissibility of the virus remains limited, as evidenced by the very small number of potential secondary infections identified through detailed contact tracing of confirmed cases [1, 2, 12–14]. …”

Both Neutralizing and Non-Neutralizing Human H7N9 Influenza Vaccine-Induced Monoclonal Antibodies Confer Protection

“…This virus reemerged in 2014 and 2015 in a seasonal pattern, causing morbidity and mortality in humans (World Health Organization, 2015). Although virus transmission occurs primarily through poultry exposure, its continuous circulation in poultry and the large number of sporadic human infections increase the chance of a new reassortment or the acquisition of mutations that could change the properties of the virus (Hu et al, 2014). To prevent H7N9 influenza infections, a live-attenuated A/Anhui/1/2013 H7N9 virus vaccine candidate was developed (Chen et al, 2014b) and evaluated in healthy individuals (Sobhanie et al, 2015).…”

Estimating Risks of Inapparent Avian Exposure for Human Infection: Avian Influenza Virus A (H7N9) in Zhejiang Province, China

“…Spatial stratified heterogeneity analyses were applied to examine the connections between poultry densities and the shortest distances to inland waters, both were proxies for inapparent avian exposure and their associations with the virus infection. Spatial clusters, which could be a confounding factor in the analyses, were estimated to adjust for potential, albeit very limited27, human-to-human transmissions. This case-control study on avian influenza viruses, compared with traditional ecological studies28, extends from the present day focus on population/group level factors in infectious-disease epidemiology to an individual-level analysis.…”