SARS-CoV-2 Serology Assay Evaluations Indicate Seropositivity Increases with Time After Symptom Onset

A head-to-head evaluation of a dozen SARS-CoV-2 serology assays has revealed several variables in their test performance, including increasing seropositivity with increasing time from symptom onset and a range of test specificities.

The US Food and Drug Administration has granted Emergency Use Authorization to dozens of serology assays measuring antibodies against SARS-CoV-2. These assays help gauge whether a person has been exposed to the SARS-CoV-2 virus and better enable estimates of viral prevalence and incidence.

Researchers from the University of California San Francisco (San Francisco, CA, USA) set out to assess the performance of these tests by comparing 10 point-of-care lateral flow assays (LFAs) and two lab-based ELISA tests for the detection of anti-SARS-CoV-2 IgM and IgG antibodies. The aim was to provide well-controlled performance data to help guide the use of serology in the response to COVID-19. The researchers tested the performance for 12 COVID-19 serology assays on a panel of 128 samples from 79 individuals with RT–PCR-confirmed SARS-CoV-2 infection and 108 pre-COVID-19 specimens.

Some of the samples were collected in the first five days after the COVID-19 patients experienced symptoms, while others were obtained further into their disease course, including samples from more than 20 days after symptom onset. The team also collected samples from 51 people with non-COVID-19 respiratory infections during the pandemic and from 108 pre-pandemic blood donor samples. The researchers found that the number of seropositive results typically increased with time from patients' symptom onset, with seropositivity peaking after more than 20 days. Four tests reached more than 80% positivity 16 days or more after symptom onset with more than 95% specificity.

"We hope these data will inform the use of serology by the medical and public health communities and provide feedback to test developers about areas of success and necessary improvement," wrote the researchers in their paper in Nature Biotechnology.

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