It remained unclear today how the victim of the first H5N1 avian influenza infection in North America, a Canadian who visited China in December, was exposed to the virus, as health authorities stressed the case's uniqueness and continued to describe the risk of further transmission as very low.
The victim, an Alberta resident, became ill while flying from Beijing to Vancouver, B.C., and on to Edmonton, Alta., on Dec 27, and died on Jan 3, Canadian officials reported yesterday. They have not released any identifying information about the person.
Canadian health officials at a press conference yesterday said the person did not leave Beijing during the China visit and did not visit any high-risk sites such as poultry markets. And the World Health Organization (WHO) said today that the person had no reported contact with poultry, animals, or sick people. The WHO also revealed that he or she was in Beijing from Dec 6 to 27.
China has not reported any human H5N1 cases since February 2013, and the country's latest confirmed H5N1 poultry outbreak was reported a week ago in Guizhou province in southwestern China, a long way from Beijing.
The last two human H5N1 cases reported in China also occurred in Guizhou province, in February 2013. Reports at the time said the two patients had no history of exposure to poultry.
Meanwhile, the US Centers for Disease Control and Prevention (CDC), in a statement posted late yesterday, commented on the uniqueness of the Canadian case.
"This is the first detected case of human infection with avian influenza A H5N1 virus in North or South America. It also is the first case of H5N1 infection ever imported by a traveler into a country where this virus is not present in poultry," the agency said.
Officials said yesterday that no symptoms have been reported in any contacts of the victim, including two traveling companions. Contacts are receiving preventive antiviral treatment, according to the WHO, which said the victim had just one traveling companion.
The CDC called the health risk posed by the case very low and is not recommending any special actions by the public in response to it. Nonetheless, the agency said it would send clinicians a reminder about when and how to test for H5N1.
"The detection of one isolated case of H5N1 virus infection in a returned traveler does not change the current risk assessment for an H5N1 pandemic," the CDC said. "A pandemic would only result if the H5N1 virus were to gain the ability to spread efficiently from person-to-person and there is no indication that this has occurred."
ECDC says risk unchanged
The European Centre for Disease Prevention and Control (ECDC) reached a similar conclusion, saying today that its last H5N1 risk assessment, issued a year ago, is still valid.
"The risk of secondary and co-primary cases among the close contacts of this case is considered to be very low for the following reasons: more than 10 days has passed since onset of the disease, transmission of A(H5N1) on board aircrafts has never been documented, and there is no evidence of sustained human-to-human transmission of A(H5N1) ever occurring," the ECDC said.
"The risk of health care associated transmission in Canada is considered very low for the same reasons."
Canada's deputy chief public health officer, Gregory Taylor, MD, recommended yesterday that travelers to places where avian flu circulates should avoid high-risk areas such as poultry farms and live-animal markets, avoid unnecessary contact with birds, avoid surfaces that have droppings on them, and make sure that all poultry dishes are well-cooked.
With the new case, the WHO's tally of confirmed H5N1 cases since 2003 stands at 649, with 385 deaths, for a case-fatality rate of 59%. Most patients had exposure to poultry, but human-to-human transmission is regarded as probable in a few cases that involved prolonged close contact between family members.
As reported previously, the Canadian patient's presentation was somewhat unusual, though not unprecedented, in that there were no respiratory symptoms, officials said. James Talbot, MD, PhD, Alberta's chief medical officer of health, said the patient's diagnosis at the time of death was meningoencephalitis, or inflammation of the brain and the lining around it, according to a report in the Edmonton Journal.
"That is one of the ways H5N1 patients die," Talbot said.
Jan 9 WHO statement
Jan 8 CDC statement on case
CDC information on H5N1 in humans
Jan 9 ECDC update
Jan 9 Edmonton Journal story
Feb 11, 2013, CIDRAP News story on two H5N1 cases in China
Dec 10, 2013, WHO H5N1 case count (does not include new case)
Jan 8 CIDRAP News story "Fatal H5N1 case in Canada is North America's first"