Criteria

Case definitions

Case definitions have been published by the Centers for Disease Control and Prevention (CDC), World Health Organization (WHO), and Ministry of Health (Saudi Arabia).[89][90][91] Since MERS is considered an emerging disease, definitions are constantly evolving and not all clinical presentations will fit the case definitions. Physicians should be vigilant for identifying suspected cases, regardless of whether they fit the case definitions or not. For example, the absence of fever has been reported in cases of confirmed infection, despite some definitions including fever as a prerequisite for diagnosis.

CDC: interim patient under investigation (PUI) guidance and case definitions[91]

Patient under investigation (PUI):

  • A person with both clinical features and an epidemiologic risk

  • Severe illness:

    • fever (may be absent in specific patient groups) and pneumonia or acute respiratory distress syndrome (based on clinical or radiologic evidence) PLUS a history of travel from countries in or near the Arabian Peninsula within 14 days before symptom onset, or close contact with a symptomatic traveler who developed fever and acute respiratory illness (not necessarily pneumonia) within 14 days after traveling from countries in or near the Arabian Peninsula, or a member of a cluster of patients with severe acute respiratory illness of unknown etiology in which MERS is being evaluated.

  • Milder illness:

    • fever (may be absent in specific patient groups) and symptoms of respiratory illness (e.g., cough, dyspnea) PLUS a history of being in a healthcare facility (as a patient, worker, or visitor) within 14 days before symptom onset in a country or territory near the Arabian Peninsula in which recent healthcare-associated cases of MERS have been identified

    • fever (may be absent in specific patient groups) or symptoms of respiratory illness (e.g., cough, dyspnea) PLUS close contact (i.e., within approximately 6 feet or the room/care area of a case for a prolonged period of time [such as caring for, living with, visiting, or sharing a healthcare waiting area or room with a confirmed MERS case] without recommended personal protective equipment, or direct contact with infectious secretions of a confirmed MERS case while not wearing recommended personal protective equipment).

Probable case:

  • PUI with absent or inconclusive laboratory results for infection who is a close contact of a laboratory-confirmed case.

Confirmed case:

  • Person with laboratory confirmation of infection (i.e., a positive real-time reverse transcription polymerase chain reaction [RT-PCR] on at least 2 specific genomic targets, or a single positive target with sequencing on a second).

Note: fever may be absent in the very young, elderly, immunocompromised, or patients receiving certain medications.

Centers for Disease Control and Prevention (CDC): interim patient under investigation (PUI) guidance and case definitions external link opens in a new window

WHO: case definition for reporting to WHO[90]

Probable case:

  • A febrile acute respiratory illness with clinical, radiologic, or histopathologic evidence of pulmonary parenchymal disease (e.g., pneumonia or acute respiratory distress syndrome) PLUS a direct epidemiologic link with a confirmed case PLUS testing is unavailable, negative on a single inadequate specimen, or inconclusive

  • A febrile acute respiratory illness with clinical, radiologic, or histopathologic evidence of pulmonary parenchymal disease (e.g., pneumonia or acute respiratory distress syndrome) PLUS the person resides in, or traveled to, the Middle East or in countries where the virus is known to be circulating in dromedary camels or where infections have recently occurred PLUS testing is inconclusive

  • An acute febrile respiratory illness of any severity PLUS a direct epidemiologic link with a confirmed case PLUS testing is inconclusive.

Confirmed case:

  • Person with laboratory confirmation (i.e., detection of viral nucleic acid or serology) of infection irrespective of clinical signs and symptoms. Presence of nucleic acid can be confirmed by either a positive RT-PCR result on at least 2 specific genomic targets or a single positive target with sequencing of a second target. Cases confirmed by serology require demonstration of seroconversion in 2 samples, ideally taken 14 days apart, by ELISA or immunofluorescence antibody assay and a neutralization assay.

World Health Organization (WHO): case definition for reporting to WHO external link opens in a new window

Ministry of Health (Saudi Arabia): case definition[89]

Suspected case:

  • II. Unexplained deterioration of a chronic condition in patients with congestive heart failure or chronic kidney disease who are on hemodialysis

  • III. Acute febrile illness with or without respiratory symptoms PLUS an epidemiological link

  • IV. Gastrointestinal symptoms and leukopenia or thrombocytopenia PLUS an epidemiological link.

Confirmed case:

  • A suspected case with laboratory confirmation of infection.

An epidemiological link is defined as one of the following within 14 days before symptom onset:

  • Exposure (contact within 1.5 meters) to a confirmed case of MERS-CoV infection

  • Visit to a healthcare facility where an infected patient has recently (within 2 weeks) been identified or treated

  • Contact with dromedary camels or consumption of camel products.

Ministry of Health (Saudi Arabia): case definition external link opens in a new window

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