Giuseppe
Emeritus
[Source: European Centre for Disease Prevention and Control (ECDC), full PDF document: (LINK). Edited.]
COMMUNICABLE DISEASE THREATS REPORT
Week 16, 14-20 April 2013
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Influenza A(H7N9) - China - Monitoring human cases
Opening date: 31 March 2013 Latest update: 11 April 2013
Epidemiological summary
The influenza A viruses from the first three cases 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 and 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).
Since 31 March 2013, 87 cases of human infection with influenza A(H7N9) have been reported from six provinces in eastern China with a combined population of about 330 million. Cases have been reported from Shanghai (32), Jiangsu (21), Zhejiang (27), Anhui (3), Henan (3) and Beijing (1).
The known onset dates of disease have been between 19 February and 14 April 2013, and date of disease onset is currently unknown for sixteen patients. Most cases have developed severe respiratory disease.
Seventeen patients have died (case-fatality ratio=20%). The median age is 64 years with a range between 4 and 89 years; 25 of them are females.
The Chinese health authorities are responding to this public health event with 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 avian influenza A(H7N9) was detected in samples from pigeons, chickens and ducks, and in environmental samples from live bird markets ('wet markets') in Shanghai, Jiangsu, Anhui and Zhejiang provinces. Authorities have closed markets and culled poultry in affected areas.
The Ministry of Agriculture in China reports that 47 801 tests samples have been taken from live animal markets, farms and slaughter houses. Of those, only 39 samples were positive for the H7N9 avian influenza virus, of which 38 were from Shanghai, Anhui, Zhejiang and Jiangsu provinces. One positive sample was from a wild pigeon in Jiangsu province.
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ECDC assessment
The source and mode of transmission have not been confirmed. The outbreak is caused by a reassortant avian influenza virus with low pathogenicity for birds, hence it does not cause the signal 'die-offs' in poultry associated with highly pathogenic strains of avian influenza viruses. Genetic analyses of the isolates have shown changes which suggest that the H7N9 virus may have greater ability to infect mammalian species, including humans, than most other avian influenza viruses.
Pathogenicity for humans appears to be high and higher age appears to be a risk factor for disease.
The most likely scenario is that of A(H7N9) spreading undetected in poultry populations and occasionally infecting humans who have close contact with poultry or poultry products but this will have to be validated as further data become available. At this time there is no evidence of any human-to-human transmission. More than 1 000 close contacts of confirmed cases are reported to have been followed up without evidence of person-to-person transmission.
There is one family cluster with two confirmed cases for which human-to-human transmission cannot be ruled out but where common exposure is the most likely explanation. In addition, the virus has been detected in one asymptomatic four-year-old boy during surveillance of risk groups.
The father of this boy is reported to have purchased poultry from the father of the first case in Beijing.
The rapid geographic spread and the increase of confirmed cases is likely to be the result of strengthened case finding and increased testing.
Influenza A(H7N9) test kits have been distributed to over 400 laboratories across China and this increased ascertainment is expected to provide important epidemiological information.
Actions
ECDC is closely monitoring developments and is continuously re-assessing the situation in collaboration with WHO, the US CDC, the Chinese CDC and other partners.
This epidemiological update does not change the conclusions and recommendations of the updated rapid risk assessment published on 12 April 2013. ECDC posted an epidemiological update on 18 April (link to be added).
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COMMUNICABLE DISEASE THREATS REPORT
Week 16, 14-20 April 2013
(?)
Influenza A(H7N9) - China - Monitoring human cases
Opening date: 31 March 2013 Latest update: 11 April 2013
Epidemiological summary
The influenza A viruses from the first three cases 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 and 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).
Since 31 March 2013, 87 cases of human infection with influenza A(H7N9) have been reported from six provinces in eastern China with a combined population of about 330 million. Cases have been reported from Shanghai (32), Jiangsu (21), Zhejiang (27), Anhui (3), Henan (3) and Beijing (1).
The known onset dates of disease have been between 19 February and 14 April 2013, and date of disease onset is currently unknown for sixteen patients. Most cases have developed severe respiratory disease.
Seventeen patients have died (case-fatality ratio=20%). The median age is 64 years with a range between 4 and 89 years; 25 of them are females.
The Chinese health authorities are responding to this public health event with 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 avian influenza A(H7N9) was detected in samples from pigeons, chickens and ducks, and in environmental samples from live bird markets ('wet markets') in Shanghai, Jiangsu, Anhui and Zhejiang provinces. Authorities have closed markets and culled poultry in affected areas.
The Ministry of Agriculture in China reports that 47 801 tests samples have been taken from live animal markets, farms and slaughter houses. Of those, only 39 samples were positive for the H7N9 avian influenza virus, of which 38 were from Shanghai, Anhui, Zhejiang and Jiangsu provinces. One positive sample was from a wild pigeon in Jiangsu province.
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ECDC assessment
The source and mode of transmission have not been confirmed. The outbreak is caused by a reassortant avian influenza virus with low pathogenicity for birds, hence it does not cause the signal 'die-offs' in poultry associated with highly pathogenic strains of avian influenza viruses. Genetic analyses of the isolates have shown changes which suggest that the H7N9 virus may have greater ability to infect mammalian species, including humans, than most other avian influenza viruses.
Pathogenicity for humans appears to be high and higher age appears to be a risk factor for disease.
The most likely scenario is that of A(H7N9) spreading undetected in poultry populations and occasionally infecting humans who have close contact with poultry or poultry products but this will have to be validated as further data become available. At this time there is no evidence of any human-to-human transmission. More than 1 000 close contacts of confirmed cases are reported to have been followed up without evidence of person-to-person transmission.
There is one family cluster with two confirmed cases for which human-to-human transmission cannot be ruled out but where common exposure is the most likely explanation. In addition, the virus has been detected in one asymptomatic four-year-old boy during surveillance of risk groups.
The father of this boy is reported to have purchased poultry from the father of the first case in Beijing.
The rapid geographic spread and the increase of confirmed cases is likely to be the result of strengthened case finding and increased testing.
Influenza A(H7N9) test kits have been distributed to over 400 laboratories across China and this increased ascertainment is expected to provide important epidemiological information.
An increasing incidence of sporadic cases and expansion of geographic spread in China and possibly neighbouring countries are expected over the coming weeks.
Individual imported human cases to Europe cannot be ruled out and countries need to prepare for detecting and diagnosing such cases.
Critical developments that would change this assessment would be evidence of sustained human-to-human transmission and detection of avian influenza A(H7N9) in bird populations in Europe.
Actions
ECDC is closely monitoring developments and is continuously re-assessing the situation in collaboration with WHO, the US CDC, the Chinese CDC and other partners.
The ECDC emergency operations centre was activated to Public Health Event (PHE) level 1 on 15 April to support its internal activities.
A senior ECDC expert is participating on the on-going expert mission in China jointly lead by WHO and Chinese health authorities.
This epidemiological update does not change the conclusions and recommendations of the updated rapid risk assessment published on 12 April 2013. ECDC posted an epidemiological update on 18 April (link to be added).
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