SEROLOGICAL TESTING FOR SARS-COV-2

Importance of Immunoassays for Coronavirus Control

Author: Ben Field, Associate Practice Manager, Scientific Services

On December 31, 2019, a pneumonia case in the Chinese city, Wuhan, with unknown pathological origin, was reported into the Chinese World Health Organization (WHO) office. By March 11, 2020, the virus had spread to 114 countries and had taken nearly 4,300 lives leading WHO to declare COVID-19 a global pandemic (WHO, 2020). The consequence of the worldwide spread caused international turmoil leading to isolation, economic disruption, and most significantly, tens of thousands of deaths.

Prevalence testing for pathological outbreaks aids in the containment process. Depending on the geopolitical location, containment procedures can range from quarantining infected individuals to isolating and locking down entire countries. To identify hotspots, a high volume of targeted and specific testing is required. Understanding active cases is a critical piece of the testing regimen, but what may often be overlooked is the importance of identifying those individuals previously infected and are now showing immunity to COVID-19.

Nucleic Acid Testing (NAT) using RT-PCR (reverse transcriptase-polymerase chain reaction) is typically used for detection of RNA virus infections (CDC (Center for Disease Control), 2017). These tests probe species-specific viral RNA to identify individuals with active infections. However, NAT tests are only serviceable during active cases. The immune system sweeps away viral particles and RNA as it clears the infection. Once recovered, the individual would be more likely to test negative for the disease using NAT methods.

SARS-COV-2 Antibodies

On March 18, San Miguel County in Colorado, USA, announced they had entered a partnership with United Biomedical (UBI) to test all 8,000 residents for not the virus itself, but for antibodies specific against SARS-CoV-2 (San Miguel County Department of Public Health and Environment, 2020). More specifically, the ELISA-based immunoassay test will identify, with high sensitivity, those who have seroconverted and those who remain seronegative. The importance of understanding these profiles is crucial in determining populations or individuals who likely have immunity toward reinfection and those who are still vulnerable to the virus.

The utilization of antibody testing for SARS-CoV-2 is still being investigated, but early studies show there can be value combining PCR testing with serological testing to understand the course of the infection. The majority of COVID-19 cases demonstrate an incubation period between 5 and 11.5 days; yet there are cases where this window has extended to 14 days (Lauer, 2020). With 50% of patients seroconverting at the 11th day since onset, there is intrinsic value for serological testing with the goal of understanding active infections. In some cases, antibody testing demonstrated more sensitivity than NAT after the first 7 days of infection. Ultimately, when combined with an RNA test, there can be increased confidence of SARS CoV-2 testing. Furthermore, a high titer of antibody correlates with more critical illness; thus antibody titers can be used to provide additional guidance for triaging and making public health decisions (Zhang, 2020). There are some limitations to serological testing with the main downside relating to false negatives. Due to the highly specific nature of antibody testing, there is a significant decrease in false negatives when compared to NAT. However, due to the variation in an individual’s timeline to seroconvert, an immunoassay test can result in a false negative. Depending on clinical impression and possible results from NAT tests, additional testing at a later point should be indicated.

References

CDC (Center for Disease Control). (2017, December 6). Public Health Guidance for Community-Level Preparedness and Response to Severe Acute Respiratory Syndrome (SARS). Retrieved from Severe Acute Respiratory Syndrome (SARS): https://www.cdc.gov/sars/guidance/f-lab/assays.html

JHU. (2020, March 30). Coronavirus Resource Center. Retrieved from Coronavirus COVID-19 Global Cases by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (JHU): https://coronavirus.jhu.edu/map.html

Lauer, S. (2020, March 10). The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Annals of Internal Medicine. doi:10.7326/M20-0504

San Miguel County Department of Public Health and Environment. (2020, March 11). County Announces New Partnership for Widespread Testing for COVID-19. San Miguel County, Colorado, USA.

WHO. (2020, March 11). Rolling updates on coronavirus disease (COVID-19). Retrieved from World Health Organization: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/events-as-they-happen

Zhang, Z. (2020, March 3). Antibody responses to SARS-CoV-2 in patients of novel coronavirus. medRxiv. doi:10.1101/2020.03.02.20030189

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