Report details surveillance for H7N9 in Beijing
Surveillance for pneumonia with an unknown cause and sentinel hospital-based surveillance in Beijing helped detect four cases of novel H7N9 avian flu, health officials from the city reported yesterday in Emerging Infectious Diseases. These cases were reported previously by Chinese officials, but the report offers new details.
The team analyzed samples from 39 hospitalized Beijing patients with pneumonia from April through June, as well as patients with influenza-like illness (ILI) in 23 sentinel hospitals and collaborating labs from Apr 22 through June (3,526 pharyngeal swab samples). They also obtained pharyngeal swab specimens from close contacts of H7N9 patients and from 1,422 poultry workers in five Beijing districts from Apr 19 to 28.
At the same time the poultry workers were tested, the researchers collected environmental samples from the workers' environments and elsewhere. And to complete the thorough study, they obtained samples from wild birds in 327 parks, wetlands, and nature reserves from May 3 through May 10.
Polymerase chain reaction (PCR) tests were positive for H7N9 in one of the pneumonia patients, a 7-year-old girl, as well as in her asymptomatic mother and a 4-year-old male friend, and in one of the ILI patients detected during sentinel-hospital surveillance.
Three environmental samples were positive for H7N9, but the samples were not collected from the poultry workers' environs. No samples from the workers, close contacts of H7N9 patients, or wild birds were positive for the virus.
The authors conclude, "Surveillance of patients with pneumonia of unknown etiology is preferred for early detection of severe cases. PCR is recommended for screening in sentinel hospital and laboratory-based surveillance of influenza A(H7N9)."
Sep 5 Emerg Infect Dis study
Researchers identify H7N9 site that binds to human, bird cells
Chinese researchers have pinpointed a receptor in the H7N9 influenza virus that allows it to bind to humans yet retain its ability to bind to birds, according to their study yesterday in Science.
In exploring H7N9 isolates from patients in Shanghai and Anhui province, the team found that the receptor site known as SH on the virus's hemagglutinin (HA) protein binds only to avian cells, whereas the AH receptor binds to both bird and human cells.
In addition, they found that a mutant AH called L226Q "has dual receptor binding property, indicating that other amino acid substitutions contribute to the receptor binding switch."
The authors write, "The loss of affinity for the avian receptor appears to be an important factor for the efficient human-to-human transmission; however, to date, limited human-to-human transmission has been observed for H7N9, which might be a result of retention of high affinity for the avian receptor."
They add that their study "showed that, in contrast to H5N1 HA, the Q226L substitution is not solely responsible for the avian-to-human receptor binding switch for H7 HA."
They conclude, "We believe that surveillance of H7N9 virus isolates for detection of the new amino acid substitutions is essential for the future implementation of control strategies."
Sep 5 Science abstract
