National Case Definition:Middle East Respiratory Syndrome Coronavirus (MERS-CoV)
The main goal of emerging respiratory virus surveillance is early detection of a case in Canada, and subsequently such virus surveillance informs efforts at containment and/or mitigation of this novel respiratory pathogen. This document outlines surveillance case definitions and provides instructions on reporting to the national level. More detailed information on surveillance guidelines, including recommendations for surveillance objectives, activities, laboratory testing, and reporting of results, are described in the National Surveillance Guidelines for Human Infection with Middle East Respiratory Syndrome Coronavirus (MERS-CoV).
Surveillance case definitions are provided here for the purpose of case classification and reporting to the Public Health Agency of Canada. They are based on the current level of epidemiological evidence and uncertainty, and public health response goals. These surveillance case definitions are not intended to replace clinician or public health practitioner judgment in individual patient management, or intended to be used for the purpose of infection control triage.
It should be noted that unusual severe acute respiratory illness (SARI) clusters in community or facility settings (and notably involving health care workers) should be appropriately investigated under the direction of local and provincial health authorities.
Initial screening tests specific for MERS-CoV can be performed in select laboratories (i.e. provincial public health and hospital-based laboratories); however, confirmation of diagnosis should be sought from Canada's National Microbiology Laboratory (NML) before being considered conclusive . Such cases are considered probable pending NML confirmation. For more information on appropriate specimens or targets for laboratory testing, refer to the Protocol for Microbiological Investigations of Severe Acute Respiratory Infections (SARI).
Provincial / Territorial public health authorities should report confirmed and probable cases of MERS-CoV nationally within 24 hours of their own notification. National surveillance case definitions are provided below - these are subject to change with ongoing monitoring and as understanding of MERS-CoV characteristics and risk evolve.
B. NATIONAL SURVEILLANCE CASE DEFINITIONS FOR MERS-CoV
Person Under investigation (PUI):
- A person meeting exposure1 and illness2 criteria
Note: The surveillance mechanisms and systems for identifying a PUI may vary by jurisdiction according to perceived risk, resources, supporting structures and other context.Note: Limited data suggests that MERS-CoV can present as a co-infection with other viral pathogens. The identification of one causative agent should not exclude MERS-CoV where the index of suspicion may be high.
- A person epidemiologically-linked through close contact1c to a laboratory-confirmed case and meeting illness criteria2 but in whom laboratory diagnosis of MERS-CoV is not available or negative (if specimen quality or timing is suspect).
Note: Laboratory confirmation not available: due to (a) no possibility of acquiring samples for laboratory testing for MERS-CoV either because the patient or samples are not available; or (b) laboratory diagnosis negative (i.e. negative MERS-CoV result but specimen quality or timing is suspect).
- A person meeting exposure1 and illness2 criteria and in whom laboratory screening test for MERS-CoV was positive but not confirmed by the NML.
Note:A positive screening test for MERS-CoV should meet one of the following conditions: (1) a positive PCR result for at least two different specific targets on the MERS-CoV genome; OR (2) one positive PCR result for a specific target on the MERS-CoV genome and MERS-CoV sequence confirmation from a separate viral genomic target.
Laboratory findings may take up to 7 days from specimen submission. See additional notes under PUI.
- A person with laboratory confirmation of MERS-CoV infection at Canada's National Microbiology Laboratory (NML).
The NML can confirm detection of the virus using MERS-CoV specific nucleic acid amplification tests (NAATs) and/or sequencing and though virus isolation in tissue culture.
C. Exposure and Illness Parameters
- Exposure criteria: Links within 14 daysa prior to illness2 onset to affected areasb (i.e. residence, travel history) OR close contactc with a confirmed or probable case of MERS-CoV or a traveller or resident with any acute respiratory illness returning from an affected areab. Factors that raise the index of suspicion should also be consideredd.
- Incubation period for MERS-CoV is still largely unknown but has been reported as prolonged in one documented instance of person-to-person nosocomial transmission (9- 14 days). SARS-CoV also demonstrated a prolonged incubation period (median 4-5 days; range 2-10 days) compared to other human coronavirus infections (average 2 days; typical range 12 hours to 5 days). Allowing for inherent variability and recall error and to establish consistency with other emerging respiratory virus monitoring, exposure history based on the prior 14 days is a reasonable and safe approximation.
- Affected areas: As affected areas are subject to change, consult the Summary of Assessment of Public Health Risk to Canada Associated with MERS-CoV for the most up -to -date information.
- A close contact is defined as a person who provided care for the patient, including health care workers (except those wearing appropriate PPE), family members or other caregivers, or who had other similarly close physical contact OR who stayed at the same place (e.g. lived with or otherwise had close prolonged contact within two metres) as a probable or confirmed case while the case was ill.
- Factors that raise the index of suspicion include having a history of being in a healthcare facility (as a patient, worker or visitor) OR having contact with camel or camel products (e.g. raw milk or meat, secretions or excretions, including urine), in an affected area within 14 days of illness onset.
- Illness criteria: Illness onset is defined by the earliest start of respiratory symptoms associated with the current episode. Focus is on the detection of severe acute respiratory illness (SARI) defined primarily by respiratory symptoms, i.e. fever (over 38 degrees Celsius) AND new onset of (or exacerbation of chronic) cough or breathing difficulty as well as clinical, radiological or histo-pathological evidence of pulmonary parenchymal disease (e.g. pneumonia, pneumonitis, or Acute Respiratory Distress Syndrome [ARDS]), typically associated with the need for hospitalization, intensive care unit monitoring and/or other severity marker (such as death).
Many infectious diseases present with a spectrum of illness, including mild or asymptomatic infection. Atypical MERS-CoV presentation with absent respiratory symptoms has been documented in the presence of comorbidity, notably immuno-suppression. Therefore, clinician and public health judgment should be used in assessing patients with milder or atypical presentations, where, based on contact, comorbidity or cluster history, the index of suspicion may be raised. Additional information can be found in the Interim Guidance For Containment When Imported Cases With Limited Human-To-Human Transmission Are Suspected/Confirmed In Canada.
Clinician discretion, epidemiologic context and local feasibility should be taken into account in discussion with local/provincial health authorities.
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