The identification of 3 unrelated cases of human infection with H7N9 avian influenza in China has prompted international concern.
Outbreaks of avian influenza, which primarily affects birds, may cause poultry growers to lose thousands of animals and incur large economic losses. Avian influenza also occasionally infects humans. One strain that has triggered international concern is highly pathogenic H5N1, which was first documented to infect humans in 1997, according to the World Health Organization (WHO).
Human cases of H5N1, which have generally occurred in individuals who have had direct contact with infected poultry, are worrisome because such infections cause severe symptoms and are associated with a high death rate. According to the WHO, H5N1 also has the potential to become a human pandemic strain of influenza because it circulates widely in poultry, humans lack immunity to it, it causes severe illness, and it has the potential to change into a form that is more transmissible from person to person.
Given the existing apprehension about potential pandemic spread of avian influenza strains, the emergence of a new and less well understood strain of avian influenza in humans triggered immediate concern. According to the Chinese Center for Disease Control and Prevention, 3 human cases, including 2 that resulted in death, have been documented in the country between February and mid-March. On March 31, Chinese authorities notified the WHO about 2 cases from Shanghai and 1 from the Anhui province.
All 3 individuals developed pneumonia and a high fever early in the course of infection. Although the source of the infections is unknown, the Chinese Center for Disease Control and Prevention said in a statement it was likely poultry. Chinese public health authorities were investigating for signs of human-to-human infections but noted that the 3 infected individuals did not have contact with one another. The WHO noted that no additional cases have been identified among 88 contacts of the ill individuals who are being monitored.
Eric Summers, MD, PhD, program director at the International Society for Infectious Diseases, said that the emergence of any new flu strain is worrisome because existing vaccines will not protect against a new strain and it is hard for clinicians to predict how a new strain will behave. He noted that until an emerging strain has been monitored for some time, it can be difficult to predict how virulent it will be in humans or whether it will spread from person to person.
Although detecting a new strain is not uncommon, Summers said, the quick announcement of finding a new strain is helpful because it allows clinicians and public health officials to be alert for potential cases. “Surveillance is getting better all the time,” he said.
He said that clinicians should pay attention to the announcement, but that to his knowledge, there is no reason at this time for “alarm bells to go off.”