Influenza H7N9 still killing people

Wednesday, 15 May, 2013

The number of deaths due to influenza H7N9 has now reached 35. China has had 34 deaths and Taiwan one death. The total number of confirmed cases is 130, giving a very high case fatality rate of 26.9%.

Chickens are the source of the virus and since it is a low pathogenic avian influenza (LPAI) strain, chickens carrying the virus can appear well. This is an example of a zoonotic emerging infectious disease with spillover events from chicken reservoir to human host. Chen et al (2013) demonstrated an epidemiological link between chickens and genetically similar H7N9 isolates from both chickens at the putative source and the human case. Incubation period in four humans epidemiologically linked to chickens was 3-8 days.

However, only 40% of confirmed cases appear to have had contact with chickens and human-to-human transmission is very rare. Only one instance of probable human-to-human transmission has been reported (Tang & Chen 2013). Modelling of the reproductive number of early cases obtained a Ro for human-to-human transmission of 0.28 (Nishiura et al 2013). This means humans themselves are incapable of maintaining an epidemic of the current H7N9 virus.

However, there is evidence that the avian H7N9 is genetically adapting to humans (Li et al 2013; Liu et al 2013). This is of major concern since adaptation to transmit human-to-human would be very serious.

Chinese scientists have developed a real-time PCR diagnostic test to detect Influenza A H7N9 with high sensitivity and specificity (Wong et al 2013).


Chen et al. Human infections with the emerging avian influenza A H7N9 virus from wet market poultry: clinical analysis and characterisation of viral genome. Lancet 2013 Apr 25. pii: S0140-6736(13)60903-4.

Li et al. Environmental connections of novel avian-origin H7N9 influenza virus infection and virus adaptation to the human. Sci China Life Sci. 2013 May 8. [Epub ahead of print]

Liu et al. Genomic signature and protein sequence analysis of a novel influenza A (H7N9) virus that causes an outbreak in humans in China. Microbes Infect 2013 Apr 27. pii: S1286-4579(13)00085-3. [Epub ahead of print]

Nishiura H, Mizumoto K, Ejima K. How to interpret the transmissibility of novel influenza A(H7N9): an analysis of initial epidemiological data of human cases from China. Theor Biol Med Model. 2013 May 4;10(1):30. [Epub ahead of print]

Tang RB, Chen HL. An overview of the recent outbreaks of the avian-origin influenza A (H7N9) virus in the human.
J Chin Med Assoc 2013 May 4. pii: S1726-4901(13)00103-2.

Wong et al. Molecular detection of human H7N9 Influenza A virus causing outbreaks in China. Clin Chem. 2013 May 10. [Epub ahead of print]

Image - Fig.1. Electron micrograph of new influenza A ( H7N9) virus from China. Source: CDC USA Public Health Image Libery. ID#15673/ Cynthia S. Goldsmith and Thomas Rowe.5

Posted by Rick Speare