Has human-to human transmission occurred yet?
Human-to-human transmission cannot be ruled out in a family cluster of cases that appeared in Vietnam in January 2004 and in another family cluster in March.
In January 2005 a girl in Thailand probably passed the virus to her mother. In no instance has the virus spread beyond the first human-to-human contacts or caused illness in the general community.
This sort of transmission requires very close sustained contact with an ill person.
The overwhelming majority of cases that have turned up in families have been traced to common exposures to birds rather than to other infected humans.
The World Health Organization has not changed its overall assessment of the pandemic risk.
Health care workers treating H5N1 patients, who have taken normal precautions, have not come down with bird flu.