Middle East respiratory syndrome coronavirus infection laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

Overview

Middle East Respiratory Syndrome (MERS) is a viral respiratory illness. It is caused by an emerging coronavirus, specifically a betacoronavirus called MERS-CoV (Middle East Respiratory Syndrome Coronavirus), first discovered in 2012. Being a relatively novel virus, there is no virus-specific prevention or treatment options for MERS patients. Attending to the fact that a vaccine hasn't been developed yet, enhancing infection prevention and control measures is critical to prevent the possible spread of MERS-CoV in hospitals and communities. Persons with symptoms suspicious of MERS-CoV infection need medical evaluation. According to the CDC: a certified case of MERS-CoV infection is considered an individual who shows laboratory confirmation of infection by MERS-CoV. This last one is given by a positive PCR test of ≥2 specific genomic targets or, a single positive target followed by successful sequencing of a second; while a probable case of MERS-CoV infection is an individual who has missing or inconclusive laboratory test results for the infection and that has been in close contact with another individual who is a "laboratory-confirmed case" of MERS-CoV infection. Laboratory tests, such as the PCR for MERS-CoV are available at state health departments, CDC and some international laboratories. Otherwise, MERS-CoV tests are not routinely available, despite the existence of a limited number of non-FDA-approved commercial tests.

Laboratory Tests

According to CDC guidelines:

• Investigations of MERS-CoV and other respiratory pathogens may now be conducted simultaneously and additionally, positive results for another respiratory pathogen should not hinder testing for MERS-CoV.
• Health-care providers in the United States should continue to evaluate patients for MERS-CoV infection if they develop fever and pneumonia or acute respiratory distress syndrome within 14 days after traveling from countries in or near the Arabian Peninsula.
• Providers should also evaluate patients for MERS-CoV infection, in the presence of ARDS, fever or pneumonia, and if they have been in close contact with recent travelers from the Arabian Peninsula who have fever and acute respiratory illness.
• Clusters of patients with severe acute respiratory illness, such as fever and pneumonia that requires hospitalization, must be evaluated for common respiratory pathogens and reported to local and state public health departments. In case a diagnosis isn't reached, particularly if the cluster includes health-care providers, testing for MERS-CoV should be considered, in consultation with state and local health departments. In this situation, all patients should be tested, even if they haven't had travel-related exposure.
• Laboratory confirmation of infection by MERS-CoV now requires a positive PCR test of ≥2 specific genomic targets or, a single positive target followed by successful sequencing of a second.
• Laboratory tests, such as the PCR for MERS-CoV are available at state health departments, CDC and some international laboratories. Otherwise, MERS-CoV tests are not routinely available, despite the existence of a limited number of non-FDA-approved commercial tests.

Confirmed Case

According to the CDC, a certified case of MERS-CoV infection is considered an individual who shows laboratory confirmation of infection by MERS-CoV.

Probable Case

According to the CDC, probable case of MERS-CoV infection is an individual under investigation who has missing or inconclusive laboratory test results for the infection and that has been in close contact with another individual who is a "laboratory-confirmed case" of MERS-CoV infection.

Specimen Types

The CDC recommends that priority for collection and real-time RT-PCR testing should be given to lower respiratory tract specimens. This preference is due to the fact that lower respiratory specimen testing appears to be more sensitive in the detection of MERS-CoV, when compared to specimens from the upper respiratory tract. It is recommended the collection of multiple specimens from different locations and in different time periods, in order to increase the probability of collecting and detecting the pathogen, by virtue of the potential impact of the infection by MERS-CoV, the risk of transmission and how little is known about the sensitivity of the diagnostic tests for this virus. It is also recommended that, in all cases of severe disease, priority is given to respiratory samples, particularly lower respiratory tract specimens; in the case of mild disease, upper tract specimen should be collected, if lower tract specimens cannot be obtained. Also, serum samples should be collected for serologic testing, as well as a stool sample or a rectal swab. In the presence of a negative test result from a highly suspicious patient for infection by MERS-CoV, further samples should be collected for testing. A false-negative result might be due to:

• poor specimen quality
• wrong timing of collection
• mishandled sample
• technical problem during testing

Collecting, Handling, and Testing Clinical Specimens

According to the CDC, each specimen container should be labeled with the patient’s ID number, specimen type and the date the sample was collected. The guidelines to collect and store biological specimens include:

Respiratory Specimens

Lower respiratory tract Broncheoalveolar lavage, tracheal aspirate, pleural fluid

Collect 2-3 mL into a sterile, leak-proof, screw-cap sputum collection cup or sterile dry container. Refrigerate specimen at 2-8°C up to 72 hours; if exceeding 72 hours, freeze at -70°C and ship on dry ice.

Sputum

Have the patient rinse the mouth with water and then expectorate deep cough sputum directly into a sterile, leak-proof, screw-cap sputum collection cup or sterile dry container. Refrigerate specimen at 2-8°C up to 72 hours; if exceeding 72 hours, freeze at -70°C and ship on dry ice.

Upper respiratory tract

Nasopharyngeal AND oropharyngeal swabs (NP/OP swabs)

Use only synthetic fiber swabs with plastic shafts. Do not use calcium alginate swabs or swabs with wooden shafts, as they may contain substances that inactivate some viruses and inhibit PCR testing. Place swabs immediately into sterile tubes containing 2-3 ml of viral transport media. NP/OP specimens can be combined, placing both swabs in the same vial. Refrigerate specimen at 2-8°C up to 72 hours; if exceeding 72 hours, freeze at -70°C and ship on dry ice.

Nasopharyngeal swabs

Insert a swab into the nostril parallel to the palate. Leave the swab in place for a few seconds to absorb secretions. Swab both nasopharyngeal areas.

Oropharyngeal swabs

Swab the posterior pharynx, avoiding the tongue.

Nasopharyngeal wash/aspirate or nasal aspirates

Collect 2-3 mL into a sterile, leak-proof, screw-cap sputum collection cup or sterile dry container. Refrigerate specimen at 2-8°C up to 72 hours; if exceeding 72 hours, freeze at -70°C and ship on dry ice.

Blood Components

Serum (for serologic testing)

For serum antibody testing: Serum specimens should be collected during the acute stage of the disease, preferably during the first week after onset of illness, and again during convalescence, ≥ 3 weeks after the acute sample was collected. However, since we do not want to delay detection at this time, a single serum sample collected 14 or more days after symptom onset may be beneficial. Serologic testing is currently available at CDC upon request and approval. Please be aware that the MERS-CoV serologic test is for research/surveillance purposes and not for diagnostic purposes - it is a tool developed in response to the MERS-CoV outbreak. Contact CDC’s Emergency Operations Center (EOC) (770-488-7100) for consultation and approval if serologic testing is being considered.

Serum (for rRT-PCR testing)

• For rRT-PCR testing (i.e., detection of the virus and not antibodies), a single serum specimen collected optimally during the first week after symptom onset, preferably within 3-4 days, after symptom onset, may be also be beneficial.

• Children and adults: Collect 1 tube (5-10 mL) of whole blood in a serum separator tube. Allow the blood to clot, centrifuge briefly, and separate sera into sterile tube container. The minimum amount of serum required for testing is 200 µL. Refrigerate the specimen at 2-8°C and ship on ice- pack; freezing and shipment on dry ice is permissible.

• Infants: A minimum of 1 mL of whole blood is needed for testing of pediatric patients. If possible, collect 1 mL in an EDTA tube and in a serum separator tube. If only 1 mL can be obtained, use a serum separator tube.

EDTA blood (plasma)

Collect 1 tube (10 mL) of heparinized (green-top) or EDTA (purple-top) blood. Refrigerate specimen at 2-8°C and ship on ice-pack; do not freeze.

Stool

Collect 2-5 grams of stool specimen (formed or liquid) in sterile, leak-proof, screw-cap sputum collection cup or sterile dry container. Refrigerate specimen at 2-8°C up to 72 hours; if exceeding 72 hours, freeze at -70°C and ship on dry ice.