Learning Objectives and CME/Disclosure Information

Original Launch Date: 07/15/2021

Expiration Date: 07/15/2023

ACCME PARS: 64332

This activity is intended for healthcare providers delivering care to women and their families.

After completing this activity, the participant should be better able to:

1. Describe the method used to identify the presence of SARS-CoV-2
2. Discuss the role of antibody testing in the diagnosis of COVID-19

Estimated time to complete activity: 0.25 hours

Faculty:

Susan J. Gross, MD, FRCSC, FACOG, FACMG President and CEO, The ObG Project

Disclosure of Financial Relationship

Postgraduate Institute for Medicine (PIM) requires faculty, planners, and others in control of educational content to disclose all their financial relationships with ineligible companies. All identified conflicts of interest (COI) are thoroughly vetted and mitigated according to PIM policy. PIM is committed to providing its learners with high quality accredited continuing education activities and related materials that promote improvements or quality in healthcare and not a specific proprietary business interest of an ineligible company.

The PIM planners and others have nothing to disclose. The OBG Project planners and others have nothing to disclose.

Faculty: Susan J. Gross, MD, receives consulting fees from Cradle Genomics.

Planners and Managers: PIM Planners have nothing to disclose

Method of Participation and Request for Credit

Participants must read the learning objectives and faculty disclosures and study the educational activity.

If you wish to receive acknowledgment for completing this activity, please complete the test and evaluation. Upon registering and successfully completing the test with a score of 100% and the activity evaluation, your certificate will be made available immediately.

Joint Accreditation Statement

In support of improving patient care, this activity has been planned and implemented by the Postgraduate Institute for Medicine and The ObG Project. Postgraduate Institute for Medicine is jointly accredited by the Accreditation Council for Continuing Medical Education (ACCME), the Accreditation Council for Pharmacy Education (ACPE), and the American Nurses Credentialing Center (ANCC), to provide continuing education for the healthcare team.

Physician Continuing Medical Education

Postgraduate Institute for Medicine designates this enduring material for a maximum of 0.25 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Continuing Nursing Education

The maximum number of hours awarded for this Continuing Nursing Education activity is 0.2 contact hours.

Read Disclaimer & Fine Print

• Summary
  • Specimen Collection
  • How is SARS-CoV-2 RNA Testing Performed?
  • Diagnostic Testing
  • Screening Testing
  • How Early Will a Test Be Positive?
  • Performance of RT-PCR Viral Tests
• Antibody Testing
  • General CDC Antibody Guidance
  • What Are the Different Types of Antibody Tests?
  • When Can Antibody Testing be Helpful?
  • Vaccination and Test Interpretation
• Learn More – Primary Sources

NOTE: Information and guidelines may change rapidly. Check in with listed references in ‘Learn More – Primary Sources’ to best keep up to date.

SUMMARY:

The CDC has provided guidance on both viral testing for SARS-CoV-2 as well as the role of antibody testing. Testing for the presence of the virus during the pandemic remains the current diagnostic standard. While antibody testing can play a role for public health teams to understand the spread of the disease, currently its use as a diagnostic test for individuals remains limited. A COVID-19 vaccine will not affect the results of SARS-CoV-2 viral tests.

Viral Testing

Specimen Collection

• Obtain an upper respiratory specimen for initial diagnostic testing
  • A nasopharyngeal (NP) specimen collected by a healthcare professional  or
  • An oropharyngeal (OP) specimen collected by a healthcare professional  or
  • A nasal mid-turbinate swab collected by a healthcare professional or by a supervised onsite self-collection (using a flocked tapered swab)  or
  • An anterior nares (nasal swab) specimen collected by a healthcare professional or by onsite or home self-collection (using a flocked or spun polyester swab)  or
  • Nasopharyngeal wash/aspirate or nasal wash/aspirate (NW) specimen collected by a healthcare professional
• Lower respiratory tract specimens
  • Collect and test sputum in patients who develop a productive cough | Induction of sputum is not recommended
  • Under certain clinical circumstances (e.g., those receiving invasive mechanical ventilation), a lower respiratory tract aspirate or bronchoalveolar lavage sample should be collected and tested as a lower respiratory tract specimen

How is SARS-CoV-2 RNA Testing Performed?

RT-PCR

• Usually performed using real-time reverse transcription polymerase chain reaction (RT-PCR)
  • Qualitative detection of RNA
• Multiple tests on the market that can target various genes
  • Envelope (env) | Nucleocapsid (N) | Spike (S) | RNA-dependent RNA polymerase (RdRp) | ORF1
• A positive test can only determine presence of SARS-CoV-2 RNA and not whether the virus is intact and capable of infecting others

Antigen

• Antigen tests can quickly detect fragments of proteins found on or within the virus by testing samples collected from the nasal cavity using swabs
• The benefit of antigen testing is speed, with results potentially available within minutes
• However, antigen tests, while very specific for the virus, are not as sensitive as molecular PCR tests
  • Positive antigen results: Highly accurate but higher chance of false negatives | Negative antigen results may still need PCR confirmation prior to treatment decisions or to prevent inadvertent spread of SARS-CoV-2

Note: Prior receipt of a COVID-19 vaccine should not affect the results of SARS-CoV-2 viral tests (NAAT or antigen)

Breath Sample Analysis

• FDA has issued an emergency use authorization (EUA) for a diagnostic test that detects chemical compounds in breath samples associated with a SARS-CoV-2 infection
• Test is performed by a qualified, trained operator under the supervision of a health care provider licensed or authorized by state law to prescribe tests
• Results available in <3 minutes

Diagnostic Testing

Signs or Symptoms of COVID-19

• Positive test
  • NAAT: Indicates infection regardless of vaccine status
  • Positive antigen test result may need confirmatory testing if the person has a low likelihood of SARS-CoV-2 infection (e.g., no known exposure to a person with COVID-19 within the last 14 days or is fully vaccinated or has had a SARS-CoV-2 infection in the last 3 months)
  • Isolate if positive test: Discontinue isolation 5 days after symptom onset and at least 24 hours after the resolution of any fever (without the use of fever-reducing medications) | Continue to wear mask around others for 5 additional days
    • Some individuals may require extended isolation and precautions (e.g., severely immunocompromised)
    • Testing is not recommended to determine when infection has resolved
    • Loss of taste and smell may persist for weeks or months after recovery and need not delay the end of isolation​
• Negative test
  • If symptoms are consistent with COVID-19, may be a false negative | Isolation and further discussion with healthcare professional recommended

Testing to determine resolution of infection

• May be appropriate for severe illness or immunocompromise
• “For all others, a test-based strategy is no longer recommended except to discontinue isolation or precautions earlier than would occur under the symptom-based strategy”

Screening Testing

No Symptoms and No Close Contact with Someone Known to Have a COVID-19 Infection

• Asymptomatic or presymptomatic infection contribute to community SARS-CoV-2 transmission
  • May help with re-opening of businesses, communities, and schools
• Point-of-care tests (e.g., antigen tests) can be particularly helpful due to short turn-around times
• Quarantine not required while results are pending
• Examples of screening programs
  • Testing employees in a workplace setting
  • Testing students, faculty, and staff in a school or university setting
  • Testing a person before or after travel

How Early Will a Test Be Positive and How Long Until Negative?

• In patient with COVID-19 infection who tested positive using a nasopharyngeal swab
  • Earliest detection: Day 1 of symptoms
  • Peak levels highest within week 1 and therefore probability of detection will be highest during that time
  • Viral load declines by week 3 and therefore virus more likely to be undetectable in to week 4
  • Infection severity: More virus may be present in patients with severe disease and therefore it may take longer to obtain a negative test result vs someone with a mild COVID-19 infection

Performance of RT-PCR Viral Tests

• RT-PCR specificities are close to 100% because they target specific RNA sequences of the SARS-CoV-2 virus
• False negative results may be due to
  • Inappropriate timing of collection vs symptom onset
  • Poor sampling technique (need to sample at the back of the nose)
• False positive results may occur due to lab error or contamination
• However, even with good analytic performance, PPV and NPV are related to prevalence and therefore can differ between geographic regions
  • In a setting with high COVID-19 prevalence, a negative test does not necessarily rule out the possibility that an individual is infected with SARS-CoV-2

Antibody Testing

General CDC Antibody Guidance

• According to the CDC

Antibody testing does not replace virologic testing and should not be used to establish the presence or absence of acute SARS-CoV-2 infection

Antibody testing is not currently recommended to assess for immunity to SARS-CoV-2 following COVID-19 vaccination, to assess the need for vaccination in an unvaccinated person, or to determine the need to quarantine after a close contact with someone who has COVID-19

Some antibody tests will not detect the antibodies generated by COVID-19 vaccines

Because these vaccines induce antibodies to specific viral protein targets, post-vaccination antibody test results will be negative in persons without history of previous infection, if the test used does not detect antibodies induced by the vaccine

• In general, antibodies will be detectable 7 to 14 days after illness onset and will be present in most people by 3 weeks
  • Infectiousness likely decreased by that time
  • Evidence suggests some degree of immunity will have developed
• IgM and IgG can appear together, usually within 1 to 3 weeks
  • IgG antibodies appear to persist for at least several months
  • Some individuals may be infected but will not develop antibodies
• Neutralizing antibodies can also be identified and are associated with immunity
• FDA requires companies providing antibody testing to obtain an EUA

What Are the Different Types of Antibody Tests?

• Antigenic Targets
  • Spike glycoprotein (S): Present on viral surface and facilitates virus entry
  • Nucleocapsid phosphoprotein (N): Immunodominant and interacts with RNA
  • Protein targeting is important to reduce cross-reactivity (cause of false positives which may occur with other coronaviruses like the common cold) and improve specificity
• Types of Antibody Testing
  • Binding antibody detection that use purified SARS-CoV-2 (not live virus)
    • Point-of-care (POC) tests
    • Laboratory tests that usually require skilled personnel and specialized equipment
  • Neutralizing antibody detection (none currently FDA authorized)
    • Serum or plasma is incubated with live virus followed by infection and incubation of cells
    • Can take up to 5 days to complete the study

When Can Antibody Testing be Helpful?

Antibody testing may be helpful in the following situations

• Seroconversion: In a patient who did not receive a positive viral test
  • A positive antibody test at least 7 days following acute illness onset but a previous negative antibody test may indicate new onset SARS-CoV-2 infection
• To support a diagnosis in the presence of a complex clinical situation, such as patients who present with COVID-19 complications (e.g., multisystem inflammatory syndrome and other post-acute sequelae of COVID-19)
  • Note: Due to antibody persistence, a single positive antibody test result may reflect previous SARS-CoV-2 infection and not a recent illness
• Clinical, occupational health, and public health purposes, such as serologic surveys

Vaccination and Test Interpretation

• In a person never vaccinated
  • testing positive for antibody against either N, S, or RBD indicates prior natural infection
• In a vaccinated person
  • Testing positive for antibody against the vaccine antigen target, such as the S protein, and negative for other antigen: Suggests vaccine-induced antibody and not SARS-CoV-2 infection
  • Testing positive for any antibody other than the vaccine-induced antibody, such as the N protein: Indicates resolving or resolved SARS-CoV-2 infection that could have occurred before or after vaccination
• The CDC states that

SARS-CoV-2 antibodies, particularly IgG antibodies, might persist for months and possibly years

Therefore, when antibody tests are used to support diagnosis of recent COVID-19, a single positive antibody test result could reflect previous SARS-CoV-2 infection or vaccination rather than the most recent illness

Learn More – Primary Sources:

CDC: Interim Guidelines for Collecting, Handling, and Testing Clinical Specimens from Persons for Coronavirus Disease 2019 (COVID-19)

Interim Guidelines for COVID-19 Antibody Testing in Clinical and Public Health Settings

CDC: Overview of Testing for SARS-CoV-2

Interpreting SARS-CoV-2 Test Results

The Promise and Peril of Antibody Testing for COVID-19

EUA Authorized Serology Test Performance

Related ObG Topics:

How Long Does It Take for COVID-19 Patients to Develop Antibodies?

COVID-19: Category Definitions, Symptoms and Those at Increased Risk

COVID-19 Treatment Guidelines