Scientists have reported the first likely case of direct human-to-human transmission of the deadly H7N9 bird flu virus that has killed over 40 people in China since March.
The findings provide the strongest evidence yet of H7N9 transmission between humans, but researchers stress that its ability to transmit itself is "limited and non-sustainable."
Avian influenza A (H7N9) virus was recently identified in Eastern China. As of June 30, 133 cases have been reported, resulting in 43 deaths, according to a report published on bmj.Com.
Most cases appear to have visited live poultry markets or had close contact with live poultry 7-10 days before illness onset. Currently, no definite evidence indicates sustained human-to-human transmission of the H7N9 virus.
The study reports a family cluster of two patients (father and daughter) with H7N9 virus infection in Eastern China in March 2013.
The first (index) patient - a 60 year old man - regularly visited a live poultry market and became ill five to six days after his last exposure to poultry. He was admitted to hospital on March 11.
When his symptoms became worse, he was transferred to the hospital's intensive care unit (ICU). He was transferred to another ICU on March 18 and died of multi-organ failure.
The second patient, his healthy 32-year-old daughter, had no known exposure to live poultry before becoming sick. However, she provided direct and unprotected bedside care for her father in the hospital before his admission to intensive care.
She developed symptoms six days after her last contact with her father and was admitted to hospital on March 24. She was transferred to the ICU and died of multi-organ failure.
Two almost genetically identical virus strains were isolated from each patient, suggesting transmission from father to daughter.
Forty-three close contacts of both cases were interviewed by public health officials and tested for influenza virus. Of these, one had mild illness, but all contacts tested negative for H7N9 infection.
Environmental samples from poultry cages, water at two local poultry markets, and swans from the residential area, were also tested. One strain was isolated but was genetically different to the two strains isolated from the patients.
The researchers acknowledge some study limitations, but say that the most likely explanation for this family cluster of two cases with H7N9 infection is that the virus "transmitted directly from the index patient to his daughter."
But they stress that "the virus has not gained the ability to transmit itself sustained from person to person efficiently."
"To our best knowledge, this is the first report of probable transmissibility of the novel virus person to person with detailed epidemiological, clinical, and virological data. Our findings reinforce that the novel virus possesses the potential for pandemic spread," researchers said.
