Tests on a father diagnosed with bird flu in China show he probably caught the disease from his son, raising further concerns about person-to-person transmission. These are the conclusions of authors of an Article published early Online and in an upcoming edition of The Lancet.
As of 2 April 2008, 376 cases of infection with highly pathogenic avian influenza A (H5N1) virus, with 238 deaths, had been reported from 14 countries since November 2003. Although most cases have been sporadic, some 25% of cases have occurred in clusters of two or more linked people.
Professor Yu Wang, Chinese Centre for Disease Control and Prevention, Beijing, China, and colleagues investigated the cases of these two men, diagnosed within a week of each other in December 2007 in China’s Jiangsu Province. Field and laboratory tests were done immediately to determine positive H5N1 infection in the two cases, and 91 people that they had come into close exposure with. Any contacts who became ill were tested for H5N1.
The 24-year-old son died, and his 52-year-old father survived only after receiving early antiviral treatment and post-vaccination plasma from a participant in an H5N1 vaccine trial. The son’s only plausible exposure to H5N1 was a poultry market visit six days before the onset of illness; while the father had substantial unprotected exposure to his ill son. The 91 exposed contacts gave consent for examination; of these, 78 received antiretroviral prophylaxis and two suffered mild illness – but all 91 tested negative for H5N1. The H5N1 viruses isolated from the father and son were genetically identical except for one small base change in the chain of nucleic acids making up the H5N1 genetic structure.
The authors conclude: “Limited, non-sustained person-to-person transmission of H5N1 virus probably occurred in this family cluster ….Viral characteristics required for sustained person-to-person transmission remain unknown. H5N1 clusters require urgent investigation because of the possibility that a change in the epidemiology of H5N1 cases could indicate that H5N1 viruses have acquired the ability to spread more easily among people.”
In an accompanying Comment, Dr Jeremy Farrar, Hospital for Tropical Diseases, Ho Chi minh City, Vietnam, and colleagues, say: “Whatever the underlying determinants, if we continue to experience widespread, uncontrolled outbreaks of H5N1 in poultry, the appearance of strains well adapted to human beings might just be matter of time. In the meantime, all family contacts of a patient with probable or confirmed H5N1 should be given chemoprophylaxis and placed under surveillance. Personal protection and advice must be extended to the family members and health workers visiting and looking after patients in hospital.”
They add: “Today’s study is a superb piece of work showing the benefit of a longstanding and trusting international collaboration that began during the severe acute respiratory epidemic. Such collaborations sustained over several years, centred in affected countries, and closely linked with WHO are our best chance of combating current and future threats to international health and ensuring that benefits are shared worldwide.”
Journal
The Lancet