Case definitions have been published by the Centers for Disease Control and Prevention (CDC), World Health Organization (WHO), and Ministry of Health (Saudi Arabia). 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
Patient under investigation (PUI):
A person with both clinical features and an epidemiological risk
fever (may be absent in specific patient groups) and pneumonia or acute respiratory distress syndrome (based on clinical or radiological 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 traveller who developed fever and acute respiratory illness (not necessarily pneumonia) within 14 days after travelling from countries in or near the Arabian Peninsula, or a member of a cluster of patients with severe acute respiratory illness of unknown aetiology in which MERS is being evaluated.
fever (may be absent in specific patient groups) and symptoms of respiratory illness (e.g., cough, dyspnoea) 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, dyspnoea) PLUS close contact (i.e., within approximately 2 metres 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).
PUI with absent or inconclusive laboratory results for infection who is a close contact of a laboratory-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.
WHO: case definition for reporting to WHO
A febrile acute respiratory illness with clinical, radiological, or histopathological evidence of pulmonary parenchymal disease (e.g., pneumonia or acute respiratory distress syndrome) PLUS a direct epidemiological link with a confirmed case PLUS testing is unavailable, negative on a single inadequate specimen, or inconclusive
A febrile acute respiratory illness with clinical, radiological, or histopathological evidence of pulmonary parenchymal disease (e.g., pneumonia or acute respiratory distress syndrome) PLUS the person resides in, or travelled 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 epidemiological link with a confirmed case PLUS testing is inconclusive.
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 neutralisation assay.
Ministry of Health (Saudi Arabia): case definition
I. Severe pneumonia (severity score ≥3 points on CURB 65) or acute respiratory distress syndrome (based on clinical or radiological evidence) [ CURB-65 pneumonia severity score ]
II. Unexplained deterioration of a chronic condition in patients with congestive heart failure or chronic kidney disease who are on haemodialysis
III. Acute febrile illness with or without respiratory symptoms PLUS an epidemiologic link
IV. Gastrointestinal symptoms and leukopenia or thrombocytopenia PLUS an epidemiologic link.
A suspected case with laboratory confirmation of infection.
An epidemiologic link is defined as one of the following within 14 days before symptom onset:
Exposure (contact within 1.5 metres) 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.
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