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Avian influenza A(H7N9) virus in China

Avian influenza viruses normally circulate among birds. Human infections with these viruses are rare and occur mostly after people have been in contact with infected birds.

The first human case infected with avian influenza A(H7N9) virus was reported in China in February 2013. Genetically similar influenza A(H7N9) viruses have been detected in infected humans and pigeon and poultry samples collected at live animal markets in Shanghai. Unlike highly pathogenic avian influenza strains, such as influenza A(H5N1), H7N9 is a low-pathogenic strain that is difficult to detect in poultry and other birds because it causes little or no signs of disease.

Sequence analysis indicates the virus has properties that facilitate infection of mammalian cells. Therefore, although sustained person-to-person transmission of H7N9 influenza virus has not been reported to date, the potential for such transmission exists and further close monitoring and investigation is required.

Non-sustained person-to-person spread of other avian influenza viruses is thought to have occurred in the past, most notably with avian influenza A (H5N1) viruses. Almost all of these cases occurred during unprotected, close and prolonged contact between a caregiver (mostly blood-related family members) and a very ill patient.

Of concern is the pandemic potential of this H7N9 virus, which might either adapt to enable efficient transmission among humans, or reassort gene segments with human influenza viruses during the co-infection of a single host, resulting in a novel virus that would be transmissible from person to person, such as occurred with the H1N1(2009) pandemic strain.

Current situation

As of 14 April 2014, the World Health Organization has reported 420 human infections, including 122 deaths, with onset since February 2013. There are still no signs of ongoing, efficient, or sustained human transmission of this virus. To date, all laboratory-confirmed human infections appear to have been acquired in mainland China – mostly in eastern provinces, in particular, Zhejiang, Jiangsu and Shanghai.

Avian influenza A(H7N9) infections in humans have been reported in Hong Kong (10 cases), Taiwan (2 cases) and Malaysia (1 case). All cases reported recent travel to China and most reported visits to live bird markets. The travel-related cases highlight the need to consider influenza A(H7N9) in human cases of severe acute respiratory illness with a history of recent travel to eastern China.

As there is no evidence of sustained person-to-person spread of H7N9 at this time, there has been no recommendation to restrict travel to China. However, travellers are advised to avoid poultry farms, live bird markets, or entering areas where poultry may be slaughtered, or contact with any surfaces that appear to be contaminated with faeces from poultry or other animals. Travellers should also wash their hands frequently with soap and water. Information for clinicians and laboratories can be found on the WA Health website.

Figure 1 – Epi-curve of avian influenza A(H7N9) cases and deaths by date of onset, as of 14 April 2014
Figure 1 – Epi-curve of avian influenza A(H7N9) cases and deaths by date of onset, as of 14 April 2014
Source: Provincial CDC (China), National China CDC, WHO, and news reports (external site)

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