10 Mar 2014
The risk assessment is reviewed on a regular basis and updated as required.
An outbreak of human infections with a new avian influenza A (H7N9) virus was first reported in China by the World Health Organization on April 1, 2013. The public health risk posed by avian influenza A(H7N9) virus from China to Canada is considered low at this time.
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, but no onward transmission has been detected.
There is still no evidence of sustained human-to-human transmission of avian influenza A(H7N9) virus. However, clusters suggest that limited human-to-human transmission may occur where there is close contact between cases and other people.
There is no indication that international spread has occurred, although when infected people from affected areas travel, their infection may be detected in another country. 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.
An outbreak of human infections with a new avian influenza A (H7N9) virus was first reported in China by the World Health Organization on April 1, 2013. Cases have been reported in China from twelve Provinces (Anhui, Guangdong, Guangxi, Hebei, Henan, Hunan, Fujian, Jiangsu, Jiangxi, Jilin, Shandong, and Zhejiang) and two Municipalities (Beijing and Shanghai). In addition, travel-related cases have been reported in Malaysia, Taiwan and Hong Kong. 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. As of 4 March 2014, the WHO has reported 379 confirmed human cases, including 116 deaths. The WHO’s Global Alert and Response website maintains the latest updates on the total number of cases.
Since October 2013, a second wave of human cases has been occurring. Cases have been reported in both men and women across a wide range of ages. In the first wave, most cases were being reported in middle-aged or elderly males. The age distribution in the second wave is less skewed toward older adult age groups, although more infections continue to be reported in males. Twenty paediatric cases have been reported in the second wave, compared to seven in the first wave. Atypical clinical presentation for influenza has not been reported.
The number of cases reported in the second wave thus far has exceeded the total number of cases reported in the first wave (February to May 2013, n=133). However, evidence does not support sustained human-to-human transmission although several small human clusters have been identified. The majority of cases reported since October 2013 are from the provinces of Zhejiang and Guangdong.
A rapid risk assessment published by the European Centre for Disease Prevention and Control on 26 February 2014 has identified that the most likely current scenario for China is that these outbreaks remain zoonotic outbreaks in which the virus is transmitted sporadically to humans in close contact with the animal reservoir, similar to the influenza A (H5N1) situation.
The animal reservoir(s), main exposures and routes of transmission to humans, and the distribution and prevalence of this virus among people and animals are currently under investigation; however, the WHO reports that human infection appears to be associated with exposure to live poultry or contaminated environments, including markets where live poultry is sold, for the following reasons:
Infection in health care workers is also of specific interest as infection in a healthcare worker has recently been identified. Investigation suggested possible exposure to poultry or contaminated environment as the likely source of infection, and no other associated human cases have been identified. Given the detection of several less severe cases through ILI surveillance, along with continued reporting of severe cases, continued vigilance is warrantedFootnote 1.
Closing of all live poultry markets was an effective control strategy in Shanghai, Jiangsu and Zhejiang as the number of reported human cases decreased following these closures in the spring of 2013. With an increasing number of cases being reported since the fall, some local jurisdictions have taken measures to mitigate the risk of infection by temporarily closing live poultry markets or implementing additional decontamination protocols. More cases of avian influenza A(H7N9) virus are anticipated as the influenza season progresses.
A scientific publication by the Infectious Diseases of Poverty indicates that it is necessary to regulate the poultry markets as long as poultry-to-poultry transmission is not well understoodFootnote 2. The Canadian Food and Inspection Agency (CFIA) published its “Preliminary Assessment of the Risk to Canadian Animals from the Novel H7N9 Influenza Virus Detected in China” and highlighted that: evidence to date strongly indicates that the novel H7N9 in poultry does not differ from other Influenza A viruses common in the animal population at the global level; this novel H7N9 virus is of avian origin and does not cause any severe clinical signs in poultry; and the risk to Canadian animals from the novel H7N9 influenza virus detected in China is considered to range from negligible to very low. The Food and Agriculture Organization of the United Nations (FAO) published an updated qualitative risk assessment on January 20, 2014. The FAO has identified there is an increased likelihood of avian influenza A(H7N9) spreading from an infected farm to an uninfected farm within affected areas of China, and from a known affected area to a “moderate to high-risk” area through live bird markets and live poultry movementsFootnote 6.
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 3.
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 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 4 and New England Journal of MedicineFootnote 6 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 tractFootnote 5 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.