Humoral response and PCR positivity in patients with COVID-19 in the New York City region, USA: an observational study

Abstract

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a global pandemic. The proportion of infected individuals who seroconvert is still an open question. In addition, it has been shown in some individuals that viral genome can be detected up to 3 months after symptom resolution. We investigated both seroconversion and PCR positivity in a large cohort of convalescent serum donors in the New York City (NY, USA) region.

Methods: In this observational study, we ran an outreach programme in the New York City area. We recruited participants via the REDCap (Vanderbilt University, Nashville, TN, USA) online survey response. Individuals with confirmed or suspected SARS-CoV-2 infection were screened via PCR for presence of viral genome and via ELISA for presence of anti-SARS-CoV-2 spike antibodies. One-way ANOVA and Fisher's exact test were used to measure the association of age, gender, symptom duration, and days from symptom onset and resolution with positive antibody results.

Findings: Between March 26 and April 10, 2020, we measured SARS-CoV-2 antibody titres in 1343 people. Of the 624 participants with confirmed SARS-CoV-2 infection who had serologies done after 4 weeks, all but three seroconverted to the SARS-CoV-2 spike protein, whereas 269 (37%) of 719 participants with suspected SARS-CoV-2 infection seroconverted. PCR positivity was detected up to 28 days from symptom resolution.

Interpretation: Most patients with confirmed COVID-19 seroconvert, potentially providing immunity to reinfection. We also report that in a large proportion of individuals, viral genome can be detected via PCR in the upper respiratory tract for weeks after symptom resolution, but it is unclear whether this signal represents infectious virus. Analysis of our large cohort suggests that most patients with mild COVID-19 seroconvert 4 weeks after illness, and raises questions about the use of PCR to clear positive individuals.

Funding: None.

Figure 1

Antibody responses in individuals with PCR-confirmed COVID-19 (A) Antibody testing results days after symptom onset stratified into titre categories. A longer interval between symptom onset and testing usually leads to higher titres. The highest titre category contains both 1:2880 and more than 1:2880 titres. Bars represent the mean, and error bars represent the SD. (B) Individuals with negative titres were recalled for retesting. Both the original test result and the second test result after the day of onset are shown. Negative titres were assigned a value of 1:40 for representation purposes; the dashed line represents the cutoff between positive and negative titres. Only results for individuals for whom date of symptom onset is known are shown.

Figure 2

PCR results of individuals with initially PCR-confirmed COVID-19 Viral genome was detected in nasopharyngeal swabs of individuals screened as plasma donors. Numbers of individuals who tested positive or negative after symptom resolution are shown. More than one result from an individual might be shown if tested more than once on different days. Only results for individuals for whom a date of symptom resolution was available are shown.