The risk assessment is reviewed on a regular basis and updated as required.
15 September 2015
The public health risk posed by avian influenza A (H7N9) virus to Canada is considered low based on available information at this time. The risk may change as new information arises.
Avian influenza A (H7N9) is a novel reassortant virus that was not previously known to circulate in humans. Sporadic transmission of avian influenza A (H7N9) to humans is thought to be associated with exposure to infected poultry or contaminated environments.
Available information suggests that this virus does not have the ability to transmit easily among humans. Clusters that have been reported suggest that limited human-to-human transmission may occur where there was unprotected close contact with symptomatic cases. However, there is still no evidence of sustained human-to-human transmission of avian influenza A(H7N9) virus.
Avian influenza A (H7N9) remains a widespread zoonotic virus in China. The most likely threat to Canadians remains a risk of importation to Canada from travelers infected while in China. Canada reported the first travel-related human case of H7N9 in North America on January 2015. Although travel related cases have been reported in other countries including Canada, there is no indication that international spread has occurred.
The first human cases with the novel reassortant avian influenza A (H7N9) virus were first reported to the World Health Organization (WHO) by China on March 31, 2013. Since then, additional cases have been reported in China from twelve Provinces (Anhui, Guangdong, Guangxi, Hebei, Henan, Hunan, Fujian, Jiangsu, Jiangxi, Jilin, Shandong, and Zhejiang), two Municipalities (Beijing and Shanghai) and in one autonomous region (Xinjiang Uyghur). In addition, travel-related cases have been reported in Malaysia, Taiwan, Hong Kong and Canada. Poultry and environmental samples have tested positive for avian influenza A(H7N9) in all above mentioned provinces and municipalities, except for Jilin and Beijing. Most human infections are believed to have occurred after exposure to infected poultry or contaminated environments.
Since March 2013, the WHO has reported over 600 confirmed human cases, including over 200 deaths. For the latest updates on cases and deaths please visit WHO's Global Alert and Response website.
Since the virus first emerged in 2013, outbreaks of H7N9 in humans have occurred in three waves. The beginning of the first wave was marked by the detection of the novel avian influenza A (H7N9) in three patients from China in March 2013, two cases from Shanghai and one from Anhui. Subsequent cases reported were concentrated in the Eastern Chinese Provinces of Shanghai, Zhejiang, and Jiangsu. The first wave lasted to May 2013.
The second wave of human avian influenza A (H7N9) infections began in October 2013 and ended in the spring of 2014. A change in the epidemiologic profile of H7N9 was observed in the second wave. There was a geographic shift in the distribution of H7N9 cases to the Southern Chinese Province of Guangdong, suggesting the virus became more widespread in its domestic bird reservoir. Additionally, the second wave had significantly larger amplitude than the first wave, both in terms of number of cases and deaths.
The third wave of human infections began in October 2014 with declining number of cases by the spring of 2015. The majority of cases were reported during the months of January and February in the Southern Chinese Province of Guangdong. On January 26, 2015, the first imported human case of avian influenza A (H7N9) from China was confirmed in Canada. A second case was confirmed on January 29, 2015. They are the first North Americans known to have been infected with this virus. The individuals were from British Columbia and travelled together to China. Both cases did not require hospitalization and have since fully recovered. The number of cases and deaths reported in this third wave was similar to those observed in the second wave.
Although the majority of human cases have resulted in clinically severe disease, human infections with avian influenza A (H7N9) can present with a variety of symptoms that range from mild illness to more severe disease. Children infected with the virus have mainly presented with mild or asymptomatic disease Footnote 1. Given the detection of several less severe cases through ILI surveillance, along with continued reporting of severe cases, continued vigilance is warranted Footnote 2. The WHO continues to advise countries to move forward in strengthening influenza epidemiological and virological surveillance, reporting of human infections as applicable under the IHR (2005), and other national health preparedness actions.
Evidence to date suggests a seasonal pattern to H7N9 infections in humans, peaking in the winter months and sporadic cases in the summer. The seasonal pattern observed is not unexpected as previous studies have reported greater circulation of avian influenza viruses in cooler weather and lower circulation in warmer temperatures Footnote 6.
The sex and age distribution of human cases of avian influenza H7N9 is skewed to middle aged or elderly males. This gender bias is not well understood, however it has been attributed by some researchers to cultural practices, such as live poultry markets (LPMs) predominantly being visited by males Footnote 5. There is a growing body of evidence that points to infected poultry, and contaminated environments including LPMs to be a key source of H7N9 infections in humans Footnote 1,Footnote 5,Footnote 7,Footnote 13. The vast majority (~85%) of all reported cases have had exposure to poultry or LPMs Footnote 3, Footnote 5. Recent studies indicate circulation of the virus may be amplified in LPMs with poultry to poultry transmission which may then serve as an ongoing source for H7N9 infection in humans (5). Poultry and environmental samples from several LPMs in China have tested positive for the virus with genomic sequences similar to those found in infected humans Footnote 1,Footnote 5,Footnote 7,Footnote 8. Unlike human infections with H7N9, the virus has not been reported to cause severe disease in poultry. The absence of disease in poultry makes it challenging to detect and control the virus in the poultry population.
Although the vast majority of cases have been linked to poultry exposure, there have been a number of reported clusters (2-3 cases) associated with close contacts of infected cases (3-4). Epidemiologic investigations suggest secondary transmission may have occurred in some instances in family members and care givers exposed to infected cases Footnote 1,Footnote 4. Of note, a recent healthcare associated cluster reported in Shantou, China in February 2015 points to a risk for healthcare workers Footnote 4. A study published in May 2015 reported that secondary cases of H7N9 were younger and presented with milder disease than sporadic/index cases Footnote 1,Footnote 3. These results further support other studies that indicate the detection of H7N9 cases to be biased towards older-more severe cases and are likely not capturing younger populations Footnote 3. Epidemiologic investigations of these clusters are suggestive of possible limited human-to-human transmission with no evidence of sustained transmission in the community.
No vaccine is currently publicly available for this subtype of the H7N9 influenza virus; although several candidate vaccines are undergoing clinical trials. WHO has recommended that an A/Anhui/1/2013-like virus be used for the development of A(H7N9) vaccines for pandemic preparedness purposes. There are currently no recommendations on the large-scale manufacture of avian influenza A(H7N9) vaccineFootnote 9.Laboratory testing has confirmed that the avian influenza A(H7N9) virus is susceptible to the neuraminidase inhibitors oseltamivir and zanamivir, two antiviral medications that are available in the National Antiviral Stockpile and National Emergency Stockpile System should they be needed to treat Canadians. WHO has issued guidance on the use of post-exposure antiviral chemoprophylaxis for avian influenza A(H7N9) (PDF Document).
The Agency's National Microbiology Laboratory (NML) has developed diagnostic assays (tests) allowing NML to rapidly detect the novel avian influenza A(H7N9) virus. These assays have been shared with provincial/territorial colleagues allowing provinces to do their own testing should it be required.
Sequencing of the avian influenza A(H7N9) virus by the World Health Organization (WHO) Chinese National Influenza Centre in Beijing revealed HA and NA genes from avian influenza A(H7N9) and remaining genes from A(H9N2), identifying this virus as a novel reassortant virus with all genes related to genes from Eurasian influenza A viruses from wild birds and poultry. Scientific publications in the LancetFootnote 11 and New England Journal of MedicineFootnote 10 suggest that poultry is a likely source of infection. This novel avian influenza A(H7N9) virus does not appear to cause severe illness in birds. This is different from previously identified and reported avian influenza A(H7N9) viruses in birds. Mutations in H7N9 strains have been identified that could favour high affinity interaction with human receptors in the upper respiratory tract Footnote 12 however, there has been no evidence of sustained human-to-human transmission. Presently, this avian influenza A(H7N9) virus is considered a Foreign Animal Disease (FAD) agent as there may be consequences if this pathogen were to circulate in avian populations in Canada.
Health care professionals are encouraged to maintain vigilance for cases of avian influenza A(H7N9) infection and notify the appropriate local Public Health Unit in their jurisdiction of any persons under investigation. The national interim case definition for avian influenza A(H7N9) is to be used for the surveillance of avian influenza A(H7N9). For guidance on surveillance objectives and activities, please refer to the interim national surveillance guidelines for avian influenza A(H7N9).
Provinces and Territories are asked to report confirmed cases of avian influenza A(H7N9) infection to the Public Health Agency of Canada using the Emerging Pathogens and Severe Acute Respiratory Infection (SARI) Case Report Form.
A travel health advisory is posted on the Agency's website. It does not recommend any restrictions on travel but encourages travellers to practice special precautions.
The Agency provides recommendations for infection prevention and control measures for patients presenting to hospitals, doctors offices and other clinics with suspected or confirmed infection with the avian influenza A(H7N9) virus in its Interim Guidance - Infection Prevention and Control Guidance for Acute Care Settings document. This guidance will be updated as new evidence becomes available.
Based on the clinical presentation of severe respiratory illness and death in humans, the potential for this virus to be a pandemic agent, and that the virus is currently considered a foreign animal disease agent, this avian influenza A(H7N9) virus is classified as a Risk Group 3 human and animal pathogen requiring Containment Level 3 for all proliferative in vitro or in vivo activities. Non-proliferative diagnostic/clinical activities can be conducted at Containment Level 2 with additional requirements. In the event of a non-negative human sample, it is strongly recommended that the work with the sample be stopped and the sample be transferred to the National Microbiology Laboratory (NML). In the event that a veterinary diagnostic laboratory detects a non-negative sample, the work is to be stopped and the sample be transferred to the National Centre for Foreign Animal Disease (NCFAD) as per the policy in the Foreign Animal Disease Diagnostic Laboratory Containment Standard. The biosafety advisory can be found on the Agency website.