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H7N9 avian flu kills seven and infects 23 in China

BMJ 2013; 346 doi: https://doi.org/10.1136/bmj.f2222 (Published 09 April 2013) Cite this as: BMJ 2013;346:f2222

Rapid Response:

Re: H7N9 avian flu kills seven and infects 23 in China

The outbreak of H7N9 avian influenza in China had killed 17 people and infected 82 by 18 April. Thirty one cases occurred in Shanghai city, twenty five cases occurred in Zhejiang province, twenty cases occurred in Jiangsu province, three cases occurred in Anhui province, two cases occurred in Henan province and one cases occurred in Beijing city.

One child in Beijing, who displayed no symptoms and tested positive for the H7N9 virus, was considered a carrier of the strain and has been placed under observation to see if he develops symptoms. And medical teams have found that he had contact with another child, who was confirmed as Beijing’s first case of H7N9. Beijing Health Bureau deputy director Zhong Dongpo said: "This is very meaningful because it shows that the disease caused by this virus has a wide scope. It's not only limited to critical symptoms. There can also be slight cases, and even those who don't feel any abnormality at all. So we need to understand this disease in a rational and scientific way”.

The appearance of a case with no symptoms in human could make tracing more difficult, and may also mean that many people infected don’t get seriously ill and recover quickly, making the virus is less deadly than it appears.

Although there was no evidence of human to human transmission, it does not mean that human to human transmission does not occur. And experts feared the prospect of H7N9 mutating into a form easily transmissible between humans, which would have the potential to trigger a pandemic.

The World Health Organization (WHO) said last week there was as yet no evidence of human-to-human transmission of H7N9. The close contacts of the victims reported were under observation but none were reported so far to have displayed abnormal symptoms.

H7N9 strain was not previously know to infect humans before cases turned up in China. The studies from our scientists have found that a novel reassortant avian-origin influenza A (H7N9) virus was isolated from respiratory specimens obtained from all three patients and was identified as H7N9. Sequencing analyses revealed that all the genes from these three viruses were of avian origin, with six internal genes from avian influenza A (H9N2) viruses.

Substitution Q226L (H3 numbering) at the 210-loop in the hemagglutinin (HA) gene was found in the A/Anhui/1/2013 and A/Shanghai/2/2013 virus but not in the A/Shanghai/1/2013 virus. A T160A mutation was identified at the 150-loop in the HA gene of all three viruses. A deletion of five amino acids in the neuraminidase (NA) stalk region was found in all three viruses. And close contact with infected birds is a likely source of transmission. Making the H7N9 strain hard to detect is that infected poultry display slight or no symptoms, unlike the H5N1 strain which kills birds and raged across the region in the last decade.

So many cities have closed markets that sell live poultry and ban poultry trading in a move to try to halt the spread of the H7N9. In 2003 the SARS (Severe Acute Respiratory Syndrome) killed several hundred people worldwide. And the H5N1 avian flu virus has killed 371 people in 15 countries since 2003. So we should pay more attention to the spread of H7N9.

Competing interests: No competing interests

18 April 2013
dai cong
doctor
min jiang
Department of Cadre Ward V, First Affiliated Hospital, China Medical University
No. 92 of Beier Road, Heping District, the city of Shenyang.