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Epidemiological update: Novel influenza A virus A(H7N9) in China

09 Apr 2013

On 31 March 2013, the Chinese health authorities announced that they identified a novel influenza A(H7N9) virus in three seriously ill patients.

As of 8 April 2013, 24 human cases of infection with influenza A(H7N9) virus have been reported in four provinces of China: Shanghai (11), Anhui (2), Jiangsu (8) and Zhejiang (3). Of these patients, seven people have died, fourteen show severe and three mild symptoms. No epidemiological link has been identified among the patients. 

More than 650 close contacts of the confirmed cases are being closely monitored. There are reports of a small family cluster of disease around the first patient, but this has not been confirmed by laboratory data.

The source of these infections and the mode of transmission are yet to be determined. This is the first time that human infection with influenza A(H7N9) virus has been identified.

The Chinese health authorities are responding to this public health event by enhanced surveillance, epidemiological and laboratory investigation and contact tracing. The animal health sector has intensified investigations into the possible sources and reservoirs of the virus. The authorities reported to the World Organisation for Animal Health (OIE) that A(H7N9) was detected in samples from pigeons and chickens and in environmental specimens from three markets in Shanghai. These markets have been closed and the live poultry were culled.

The influenza A viruses from the first three patients were non-subtypeable and were sent to the WHO Influenza Collaborating Centre at the Chinese Centre for Disease Control and Prevention (CCDC). The genetic comparison indicated that these cases were caused by a novel reassortant avian influenza virus with avian origin genes from both A(H7N9) and A(H9N2). No similar viruses have been seen before. In addition, A(H7N9) differs from A(H7) and A(H9) viruses that have been seen previously in Europe.

No vaccine is currently available for this subtype of the influenza virus. Preliminary test results suggest that the virus is susceptible to the neuraminidase inhibitors (oseltamivir and zanamivir).

At this time, there is no evidence of on-going human-to-human transmission. More sporadic cases are expected to be reported. The risk of disease spread to Europe is considered low, although individual cases coming from China cannot be ruled out.

Table 1: Distribution of influenza A(H7N9) cases by date of onset of symptoms, age, gender, status and province in China, as of 8 April 2013 (n=24)

Date of onset

Age

Sex

Status

Severity

Province

19/02/2013

87

M

dead

severe

Shanghai

27/02/2013

27

M

dead

severe

Shanghai

07/03/2013

38

M dead severe Zhejiang

15/03/2013

35

F

alive

severe

Anhui

19/03/2013

45

F

alive

severe

Jiangsu

19/03/2013

48

F

alive

severe

Jiangsu

20/03/2013

83

M

alive

severe

Jiangsu

20/03/2013

61

F alive severe Jiangsu

21/03/2013

32

F

alive

severe

Jiangsu

21/03/2013

79

M alive severe Jiangsu

22/03/2013

67

F alive severe Shanghai

25/03/2013

67

M

alive

severe

Zhejiang

25/03/2013

59

M alive severe Shanghai

27/03/2013

52

F dead severe Shanghai

28/03/2013

48

M dead severe Shanghai

28/03/2013

74

M alive severe Shanghai

28/03/2013

55

M alive severe Anhui

28/03/2013

85

M alive severe Jiangsu

29/03/2013

64

M

dead

severe

Zhejiang

29/03/2013

66

M

alive

mild

Shanghai

29/03/2013

67

M alive mild Shanghai

30/03/2013 

25

F

alive

severe

Jiangsu

31/03/2013

4

M

alive

mild

Shanghai

01/04/2013

64

M

dead

severe

Shanghai

 

Figure 1: Distribution of influenza A(H7N9) cases in China by week of onset of symptoms, as of 8 April 2013 (n=24)

Influenza A(H7N9) China by week of onset

Figure 2: Distribution of cumulative number of confirmed influenza A(H7N9) cases by province in China, 19 February to 8 April 2013

Influenza A(H7N9) China cumulative number by province

 

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