Novel Influenza A(H7N9) in China - Update April 15

According to the the European Center for Disease Control and Prevention 


As of 15 April 2013, 60  sixty 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. Onset of disease has been between 19 February and 9 April 2013 in: Shanghai (24), Jiangsu (16), Zhejiang (15), Anhui (2), Henan (2)and Beijing (1). The date of disease onset is currently unknown for five patients. Most cases have developed severe respiratory disease and only three cases are reported to have mild clinical course. Thirteen patients died (case-fatality ratio=21%). The median age is 65 years with a range between 4 and 87 years; 17 of them are females.

More than 1000 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 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.

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.

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 outside of China is considered low, although individual cases coming from China cannot be ruled out.

The CDC also release a HAN alert yesterday regarding the current situation as well as interim recommendations for case definitions, testing, infection control and treatment.