Household transmissibility of avian influenza A (H7N9) virus, China, February to May 2013 and October 2013 to March 2014

• Published in: Euro surveillance : bulletin européen sur les maladies transmissibles Vol. 20; no. 10; p. 21056
• Main Authors: Yang, Y, Zhang, Y, Fang, L, Halloran, M E, Ma, M, Liang, S, Kenah, E, Britton, T, Chen, E, Hu, J, Tang, F, Cao, W, Feng, Z, Longini, Jr, I M
• Format: Journal Article
• Language: English
• Published: Sweden Centre Europeen pour la Surveillance Epidemiologique du SIDA (European Centre for the Epidemiological Monitoring of AIDS) 12.03.2015
• Subjects: Animals; Avian flu; China - epidemiology; Disease Outbreaks; Disease transmission; Family Characteristics; Female; Genome, Viral; Humans; Influenza A Virus, H7N9 Subtype - isolation & purification; Influenza A Virus, H7N9 Subtype - pathogenicity; Influenza in Birds - epidemiology; Influenza in Birds - transmission; Influenza in Birds - virology; Influenza, Human - epidemiology; Influenza, Human - transmission; Influenza, Human - virology; Male; Middle Aged; Models, Biological; Mutation; Population Surveillance; Poultry; Reverse Transcriptase Polymerase Chain Reaction; Risk assessment; Zoonoses - epidemiology; Zoonoses - transmission; Zoonoses - virology; China
• ISSN: 1560-7917; 1025-496X; 1560-7917
• DOI: 10.2807/1560-7917.ES2015.20.10.21056

To study human-to-human transmissibility of the avian influenza A (H7N9) virus in China, household contact information was collected for 125 index cases during the spring wave (February to May 2013), and for 187 index cases during the winter wave (October 2013 to March 2014). Using a statistical model, we found evidence for human-to-human transmission, but such transmission is not sustainable. Under plausible assumptions about the natural history of disease and the relative transmission frequencies in settings other than household, we estimate the household secondary attack rate (SAR) among humans to be 1.4% (95% CI: 0.8 to 2.3), and the basic reproductive number R0 to be 0.08 (95% CI: 0.05 to 0.13). The estimates range from 1.3% to 2.2% for SAR and from 0.07 to 0.12 for R0 with reasonable changes in the assumptions. There was no significant change in the human-to-human transmissibility of the virus between the two waves, although a minor increase was observed in the winter wave. No sex or age difference in the risk of infection from a human source was found. Human-to-human transmissibility of H7N9 continues to be limited, but it needs to be closely monitored for potential increase via genetic reassortment or mutation.