1, the source of infection has so far been isolated to the avian h5n1 influenza virus hosts are: (1) birds, including ducks (mallard), chickens, turkeys, quail, geese, pigeons, black-headed geese, spotted geese, fish eagles, black-headed gulls, sparrows, etc.; (2) mammals, such as tigers, leopards, cats, pigs and people. Therefore, infected avian and mammalian animals, including the infected population, can be potential sources of a(h5n1) infection to infect people or even become a source of infection leading to human transmission. At present, the most important source of infection is still infected poultry animals, especially free-range poultry. From the phenomenon of family gathering, human avian influenza patients may also have a certain degree of contagiousness. 2, the transmission route Infection of the human body is mainly through inhalation of infectious droplets or droplet nuclei, direct contact or indirect contact through contaminants, inoculating the virus into the patient’s upper respiratory tract or the mucosa of the conjunctiva. The relative transmission efficiency of the different transmission routes has not been determined. Most current evidence suggests the existence of avian-human transmission, environmental-human transmission, and vertical mother-to-child transmission, with minority and non-continuous evidence supporting limited interpersonal transmission. 3. susceptible populations The majority of human cases of subtype avian influenza are young people and children, which is quite different from seasonal influenza. the mean age of human avian influenza cases in Hong Kong in 1997 was 17.2 years (1-60 years). who analyzed 202 confirmed human avian influenza cases reported since the end of 2003, the median age was 20 years (3 months-75 years). 50% of cases were younger than 20 years and 90% of cases were Fifty percent of the cases were younger than 20 years, and 90% of the cases were younger than 40 years. Among the cases younger than 10 years, 21 cases were younger than 5 years and 32 cases were between 5 and 9 years old. The median age of our 23 cases was 29 years (6-62 years), which occurred mainly in young adults, with most cases occurring in rural areas. 4, the incubation period and the infectious period (1) incubation period: the definition of the incubation period of human avian influenza after exposure has yet to be determined, and is now mostly estimated by the interval between the time of the last exposure and the onset of the case, generally within 1 week. 1997 most cases in Hong Kong onset 2-4 days after exposure, 17 patients in Thailand onset 2-8 days after exposure (median 4 days), 10 patients in Vietnam onset 2-4 days after exposure (median 4 days). -4 days after exposure (median 3 days), and 14 patients in China had onset of disease 1-5 days after exposure (median 4 days). The median incubation period was estimated to be 4 days (1-5 days) by specifying the interval between the time of last exposure and the onset of disease. (2) Infection period: The protective neutralizing antibody in the serum of human avian influenza patients peaks about 2 weeks after infection, and the peak titer of the antibody can be maintained for about 2 months, and its infectiousness is greatly reduced after the formation of neutralizing antibody in the organism.