H7N9: What you need to know.

Avian influenza A(H7N9) is a subtype of influenza viruses that have been detected in birds. The first reported human infection occurred on March 31, 2013 in China. Since then, sporadic infections in both humans and birds have been observed. Most of the cases of human infection with this avian H7N9 virus have reported recent exposure to live poultry or potentially contaminated environments, especially markets where live birds have been sold. This virus does not appear to transmit easily from person to person, and sustained human-to-human transmission has not been reported.

As of April 8, 2017, the Center for Health Protection and Department of Health (China) had reported 581 human infections with Asian H7N9 virus during the 5th epidemic. This brings the total cumulative number of human infections with Asian lineage H7N9 reported by WHO to 1,381. During epidemics one through four, about 40 percent of people confirmed with Asian H7N9 virus infection died. Characteristics of the fourth epidemic included greater percentages of patients admitted to intensive care units and with diagnoses of pneumonia, identification of the virus in new areas, a greater percentage of infected persons living in rural areas, and a longer epidemic period. Genetic changes in the virus have not been sufficient to alter antigenic properties or cause mismatch with candidate vaccines.

Most human infections with avian influenza viruses, including Asian H7N9 virus, have occurred after exposure to poultry; Asian H7N9 viruses continue to circulate in poultry in China. Most reported patients with H7N9 virus infection have had severe respiratory illness (e.g., pneumonia). In most cases, infection with A(H7N9) virus is characterized by high fever, cough, shortness of breath and rapidly progressing severe pneumonia. Complications include acute respiratory distress syndrome (ARDS), septic shock and multi-organ failure requiring intensive care. Severe illness and fatal outcome have been more frequently observed in pregnant women, in older persons and those with underlying chronic conditions. Asymptomatic and mild infections with A(H7N9) virus have been detected, but the underlying rate of such infections is not well understood.

Rare instances of limited person-to-person spread of this virus have been identified in China, but there is no evidence of sustained person-to-person spread. Some human infections with Asian H7N9 have been reported outside of mainland China, but most of these infections have occurred among people who had traveled to mainland China before becoming ill. Asian H7N9 viruses have not been detected in people or birds in the United States.

While the current risk to the public’s health posed by Asian H7N9 virus is low, the pandemic potential of this virus is concerning. Influenza viruses constantly change and it is possible that this virus could gain the ability to spread easily and sustainably among people, triggering a global outbreak of disease. In fact, of the novel influenza A viruses that are of special concern to public health, Asian lineage H7N9 virus is rated by the Influenza Risk Assessment Tool (IRAT) as having the greatest potential to cause a pandemic.

It is likely that sporadic human infections with Asian H7N9 virus associated with poultry exposure will continue to occur in China. There is also a possibility of Asian H7N9 virus spreading to poultry in neighboring countries and human infections associated with poultry exposure may be detected in neighboring countries. Asian H7N9 infections may continue to be detected among travelers returning from countries where this virus is present. However, as long as there is no evidence of ongoing, sustained person-to-person spread, the public health risk assessment would not change substantially. Responding to this threat, there is a need for a national containment-control-eradication program in poultry, in addition to effective A(H7N9) virus surveillance and continued risk assessment among humans and poultry in China and neighboring countries.


Centers for Disease Control and Prevention: Link 1, Link 2


World Health Organization: Link 1, Link 2, Link 3, Link 4


Center for Infectious Disease Research and Policy: Link


Food and Agriculture Organization of the United Nations: Link


Center for Health Protection: Link