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Summary of Assessment of Public Health Risk to Canada Associated with Middle East Respiratory Syndrome Coronavirus (MERS-CoV)

21 Dec 2014
The risk assessment is reviewed on a regular basis and updated as required.

Updated: December 16, 2014

Risk Assessment

  • The public health risk posed by MERS-CoV to Canada is considered low based on available information at this time. Further investigation of basic epidemiological indicators is required to guide effective control measures, and the risk may change as new information arises.
  • Some of the infections have occurred in clusters of close contacts or in health care settings. This provides good evidence of human-to-human transmission possibly involving different modes of transmission. To date, no sustained human-to-human transmission has been observed. There is strong evidence that direct and indirect contact with camels is implicated in disease transmission.
  • 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. The last exported case to a country outside the Middle East was in May 2014.
  • Additional cases of MERS-CoV infection are expected to be reported from the Middle East. Additionally, it is likely that cases will continue to be exported to other countries by tourists, travellers, guest, workers or pilgrims who might acquire infection following exposure to an animal or human source.
  • The WHO International Health Regulations Emergency Committee met on June 16, 2014 and has determined that the conditions for a Public Health Emergency of International Concern have not yet been met, but that the situation continues to be of concern.

Event Summary

Since April 2012, cases of Middle East Respiratory Syndrome (MERS-CoV) have been reported in 22 countries in the Middle East (Saudi Arabia, Qatar, Jordan, the United Arab Emirates (UAE), Oman, Kuwait, Yemen, Lebanon, Iran and Turkey), in Europe (the United Kingdom (UK), France, Italy, Greece, Germany, the Netherlands and Austria), in Africa (Tunisia, Egypt and Algeria), in Asia (Malaysia) and in the Americas [the United States of America (USA)] . All the European, North African, Southeast Asian, and North American cases have had a direct or indirect connection to the Middle East. However, in France, Italy, Tunisia and UK, there has been limited local transmission among close contacts that had not been to the Middle East. There have been no cases identified in Canada.

As of December 16, 2014, the World Health Organization (WHO) has reported 938 confirmed human cases, including 343 deaths. For the latest updates on cases and deaths please visit the Global Alert and Response website.External Link

An increasing incidence of MERS-CoV from March-April for the third consecutive year suggests a seasonal pattern. The apparent seasonal increase in primary cases occurring for unknown reasons may be related to the weaning of young camels from their mothers in the spring of each year. In light of this, the WHO recommends avoiding contact with camels; not drinking raw camel milk or camel urine; and not eating meat that has not been thoroughly cooked.

Several cases reported appear to be secondary cases. The majority of secondary cases are mainly healthcare workers who have been infected within the healthcare setting, although several patients who were in the hospital for other reasons are also considered to have been infected with MERS-CoV in the hospital. The majority of the infected healthcare workers presented with no or minor symptoms. Between early April and early June 2014, over 25% of cases reported have occurred among Health Care Workers.

A large proportion of recently reported cases have likely acquired infection through human-to-human transmission and only about a quarter are considered primary cases. This suggests slightly more human-to-human transmission than previously observed, however at this stage it is difficult to determine if the increase is as a result of: (1) a change in transmissibility with current levels of surveillance missing cases of mild infection in the community; or (2) due to a breakdown of infection, prevention and control measures in addition to more intensive contact tracing and screening.

Many aspects of transmissions patterns support the second suggestion. For example, cases resulting from human-to-human transmission have milder disease or no symptoms. Please refer to the WHO risk assessmentExternal Link and the European Centre for Disease Prevention and Control (ECDC) risk assessmentExternal Link for additional details of the different hypotheses around transmission patterns. For additional information on infection prevention and control measures, please refer to the infection control section.

Since early 2014 two large outbreaks have been reported in Saudi Arabia and the UAE. The first outbreak occurred in a hospital in Jeddah, Saudi Arabia. On a mission, the WHO analyzed 128 laboratory-confirmed cases that had symptom between February 17 and April 26, 2014. An estimated 60% of all cases analyzed were reported in a hospital setting. A second hospital outbreak occurred in the UAE and resulted in a total of 28 cases in the city of Al Ain. It is unclear whether transmission occurred from the index case or from non-human sources. The number of laboratory-confirmed MERS-CoV in Saudi Arabia and the UAE has decreased in the month of May 2014.

In their latest publication, the WHO provides recommendations for the general population as well as for high risk groups which include: (1) practicing general hygiene measures for those visiting places where camels are present and (2) handling with care animal products in order to avoid cross-contamination with uncooked foods.

The IHR Emergency Committee concerning MERS-CoV had a meeting on June 16, 2014. The consensus was that the conditions for a public health emergency of international concern (PHEIC) had not yet been met. The committee indicated that the situation remains serious in terms of public health impact. They indicated that there is a need to further analyze hospital outbreaks to better understand where breaches in infection control and prevention measure occur.

Summary of literature

A modelling study published in November 2013 has estimated that at least 62% of symptomatic cases may have gone undetected note 1. This is not unusual as many surveillance systems are often unable to capture mild and asymptomatic cases. However, there is insufficient epidemiological information to determine whether transmission is self-sustaining in humans and also, what role mildly symptomatic and asymptomatic cases play in disease transmission.

Recent studies support the idea that camels serve as a primary source of MERS-CoV in infection humans, and that other livestock are not involved. The discovery of the route of transmission between camels and humans remains critical to stopping initial introduction into human populations. The limited data available on exposures of primary cases (patients who do not appear to have contracted infection from another human) suggests that transmission is often indirect note 2. There continues to be a need for well planned, structured investigations carried out in conjunction with exposure investigations in humans.

In a study published on May 14, 2014, the U.S. Centers for Disease Control and Prevention (CDC) describes their experience with their first two MERS-CoV cases on American soil Footnote 4. Infection prevention and control methods included self-monitoring, use of mask, voluntary house quarantine and guidelines around timing for HCWs returning to work following exposure to MERS-CoV (consult article for full details). The U.S. CDC has also upgraded their travel alert to a level 2 which includes enhanced precautions when traveling to countries in or near the Arabian Peninsula and are planning to work in health care settings.

No vaccine or effective antiviral treatment is currently available for MERS-CoV. However, in an article published in mBio on September 10, 2013 researchers from the University of Madrid developed a mutant strain of the MERS-CoV virus that may be used as a basis for a safe and effective vaccine against MERS-CoV once safeguards can be engineered note 3. Additional work is still required before clinical trials can begin, as only one safeguard is currently in place and the US FDA requires at least three to ensure the virus does not revert to its virulent form.

On 8 August 2013, WHO issued an advice note (PDF Document)External Link on home care for patients infected with MERS-CoV. This was developed to meet the urgent need for recommendations on the safe home care for patients with MERS-CoV infection presenting with mild symptoms and public health measures related to management of asymptomatic contacts.

On 28, April 2014, the WHO published guidelines for Infection prevention and control of epidemic and pandemic prone acute respiratory infections in health careExternal Link. The guidelines are fully applicable to MERS-CoV.

The WHO has published travel advice on MERS-CoV for pilgrimages on June 3, 2014 note 5. The advisory identifies key groups to consider for risk communication on a range of issues before, during and after Umra and Hajj and describes actions for countries to take in preparation for Umra and HajjExternal Link.


Footnote 1
Cauchemez S, Fraser C, Van Kerkhove MD, et al. Middle East respiratory syndrome coronavirus: quantification of the extent of the epidemic, surveillance biases, and transmissibility. Lancet Infect Dis. 2013. http://dx.doi.org/10.1016/S1473-3099(13)70304-9
Footnote 2
World Health Organization. Middle East respiratory syndrome coronavirus (MERS-CoV) Summary and literature update - as of 27 March 2014. http://www.who.int/csr/disease/coronavirus_infections/MERS_CoV_Update_27_March_2014.pdf?ua=1
Footnote 3
Almazán F, DeDiego ML, Sola I, et al. 2013. Engineering a replication-competent, propagation-defective Middle East respiratory syndrome coronavirus as a vaccine candidate. mBio 4(5):e00650-13. doi:10.1128/mBio.00650-13.
Footnote 4
Bialek SR, Allen D, et al. First Confirmed Cases of Middle East Respiratory Syndrome Coronavirus (MERS-CoV) Infection in the United States, Updated Information on the Epidemiology of MERS-CoV Infection, and Guidance for the Public, Clinicians, and Public Health Authorities-May 2014. MMWR. 2014. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm63e0514a1.htm
Footnote 5
World Health Organization. World-travel advice on MERS-CoV for pilgrimages.
http://www.who.int/ith/updates/20140603/en/

Virus Characteristics

Five virus isolates have been cultured and genome sequences have been made publicly available. All five of the sequenced viruses have a high degree of genetic similarity. Preliminary analyses show that the viruses are genetically somewhat similar to bat coronaviruses, but distinct from the Severe Acute Respiratory Syndrome coronavirus (SARS-CoV) which caused an international outbreak in 2003 in humans.

It should be noted, however, that the similarity does not necessarily imply that bats are the reservoir for the human virus or that direct exposure to bats or bat excreta were responsible for infection. In vitro studies suggest that MERS-CoV has the potential to have a broad host range. This likely facilitates its zoonotic behaviour but means that a wide range of natural and domesticated animal reservoir species is possible. MERS-CoV itself has not yet been isolated from an animal.

Recommendations for Canada

Surveillance

Health care professionals are encouraged to maintain vigilance for cases of MERS-CoV infection, and notify the appropriate Public Health Departments of any persons under investigation. The national interim case definition for MERS-CoV is to be used for the surveillance of MERS-CoV. For guidance on surveillance objectives and activities, please refer to the interim national surveillance guidelines for MERS-CoV.

Provinces and Territories are asked to report confirmed cases of MERS-CoV infection to the Public Health Agency of Canada using the Emerging Respiratory Pathogens and Severe Acute Respiratory Infection (SARI) Case Report Form.

Laboratory

There is evidence that lower respiratory tract specimens such as bronchoalveolar lavage, sputum and tracheal aspirates contain the highest viral loads and should be collected when possible. The importance of upper respiratory tract specimens such as nasopharyngeal/ oropharyngeal swabs has also been demonstrated, therefore it is recommended that both upper and lower respiratory tract specimens be collected whenever possible. To increase the likelihood of detecting the virus, multiple samples from multiple sites should be collected over the course of the illness. Even after the initial detection of the virus, continued sampling and testing will add to current knowledge about the duration of virus shedding and is strongly encouraged. Virus has been detected in urine and faeces but at levels below those found in the lower respiratory tract. To date, there is little information on the value of whole blood as a specimen for MERS-CoV detection.

To consider a case as laboratory-confirmed, one of the following conditions must be met:

  • A positive PCR result for at least two different specific targets on the MERS-CoV genome, OR
  • One positive PCR result for a specific target on the MERS-CoV genome and an additional different PCR product sequences, confirming identity to known sequences of MERS-CoV.

Serological testing can provide valuable information on rates of infection in populations, and serum samples should be collected. Paired samples are preferred and should be collected 14-21 days apart, with the first being taken during the first week of illness. If only a single sample is to be collected, it should be done at least 14 days after symptom onset. It is recommended that any positive result by a single serological assay should be confirmed with a neturalization assay. At present, there is no clear consensus on the interpretation of serological test results in individual patients. Given that currently available assays have been validated using only a limited number of convalescent sera, it is prudent to take a caution approach when confirming cases based solely on serological testing. For the time being, cases where the testing laboratory has reported positive serological test in the absence of PCR testing or sequencing, are considered probable cases of MERS-CoV infection, if they meet the other conditions of the case definition.

Source: Laboratory testing for Middle East Respiratory Syndrome Coronavirus Interim Recommendations September 2013External Link (PDF Document)

The Agency's National Microbiology Laboratory (NML) has developed two serology assays and is in the process of acquiring samples for further validation. Provincial/territorial colleagues have been made aware of these tests.

Travel Health Notice

A travel health notice is posted on the Agency's website. It does not recommend any restrictions on travel but encourages travelers to take routine precautions.

Infection Control

Health care facilities are reminded of the importance of systematic implementation of infection prevention and control (IPC) measures. Health care facilities that provide care for patients suspected or confirmed with MERS-CoV infection should take appropriate measures to decrease the risk of transmission of the virus to other patients, health care workers and visitors. Recommendations for infection prevention and control measures for patients presenting with suspected or confirmed infection or co-infection with MERS-CoV in acute care settings is posted on the Agency's website. This guidance will be updated as new information becomes available.

Biosafety

MERS-CoV is classified as a Risk Group 3 human pathogen given that this virus can cause serious illness in humans, while the public health risk is low since the risk of spread of the virus in the community appears to be low. Containment Level 3 is required for all proliferative work (in vitroor in vivo), and non-proliferative diagnostic activities can be conducted at Containment Level 2 with the use of additional operational practices as outlined in Biosafety Advisory: Middle East Respiratory Syndrome Coronavirus (MERS-CoV).

The WHO has published interim recommendations for laboratory testing for MERS-CoV (19 February 2013).