Wendy Wu ’22
COVID-19 is a disease caused by a newly discovered coronavirus: SARS-CoV-2. First identified in Wuhan, China in late 2019, the coronavirus disease has become a pandemic within a matter of months, causing worldwide panic and hysteria. In this short time, nations and the World Health Organization struggled to contain the outbreak. In addition to treatment and vaccines, developing a test for COVID-19 was of utmost importance. Viral nucleic acid detection using real-time polymerase chain reaction (RT-PCR) assay was approved by the CDC in early 2020 and remains the standard diagnostic test for COVID-19. RT-PCR, however, is slow, expensive and requires special equipment, which may limit its usage in remote areas. Fei Xiang, a medical student in the Department of Respiratory and Critical Care Medicine at Union Hospital, along with her colleagues, aimed to study the antibody response to COVID-19 and the value of antibody assays, a more efficient diagnostic test, in detecting COVID-19 pneumonia.
Prior to the study, research was conducted in regards to the 2003 SARS epidemic. Xiang’s team identified Immunoglobulin M and G (IgM and IgG, respectively) as antibodies of interest. The team analyzed the antibody responses to SARS-CoV-2 in 109 patients with confirmed or suspected diagnoses at Union Hospital. The detection of IgM and IgG were based on a sandwich enzyme linked immunosorbent assay (ELISA). Serum collected from patients were diluted, added to a 96-well microplate, and incubated for an hour at 37℃. The samples underwent two more cycles—30 and 15 minutes, respectively—of incubation, after which stop solution was added to terminate the reaction. The researchers calculated antibody concentrations for each sample. The team used these values to analyze the diagnostic value of ELISA-based antibody tests based on sensitivity, specificity, positive predictive value, negative predictive value, and accuracy.
Based on 216 serum samples from the 85 patients confirmed with COVID-19 pneumonia, IgM and IgG antibodies were detected positive within four to seven days of symptom onset. Patients were tested over multiple days to determine the rate of seroconversion (change from seronegative to seropositive). IgM seroconversion increased rapidly after nine days from onset, while IgG seroconversion increased rapidly after 11 days. Nearly all patients were seropositive after a month. These results demonstrated that ELISA-based antibody tests show great specificity and positive predictive value for COVID-19. Ultimately, because IgM and IgG antibodies could be detected in the middle and late stages of SARS-CoV-2, antibody tests could be especially useful in diagnosing the disease in chronic patients. As an emerging infection, there is still much to know about the novel coronavirus. Further research may result in better testing, identification of more antibodies involved, and, hopefully, better treatment and preventative measures.
 F. Xiang, et al., Antibody detection and dynamic characteristics in patients with COVID-19. Clinical Infectious Diseases (2020). doi: 10.1093/cid/ciaa461.
 Image retrieved from: technologyreview.com/2020/04/02/974964/the-coronavirus-test-that-might-exempt-you-from-social-distancingif-you-pass/.