Persistence of SARS-CoV-2 nasopharyngeal swab PCR positivity in COVID-19 convalescent plasma donors

Abstract

Background: Nucleic acid persists after symptom resolution and infectivity for many viral infections via delayed clearance of nucleic acid fragments, non-infectious particles, or transmissible virus. For Coronavirus Disease 2019 (COVID-19), the relationship between nasopharyngeal (NP) swab positivity, the development of antibodies against COVID-19, and clinical history are unclear.

Study design and methods: Individuals who recovered from COVID-19 and volunteered to donate convalescent plasma (CP) were screened by NP swab PCR, responded to a questionnaire, and were tested for anti-COVID-19 antibodies.

Results: A proportion of 11.8% of individuals tested positive for SARS-CoV-2 by NP swab PCR greater than 14 days after the resolution of symptoms of active disease, including one donor who had asymptomatic disease and tested positive by NP swab 41 days after her initial diagnosis. Clinical history did not show a significant correlation with persistence of NP swab positivity. Also, NP swab positivity >14 days from symptom resolution did not correlate with anti-COVID-19 serology results. IgG anti-SARS-CoV-2 spike antibody strength correlated with hospitalization for COVID-19 using two different assays. Total anti-SARS-CoV-2 nucleocapsid antibody strength correlated with time from symptom resolution to sample collection and symptom duration.

Conclusions: SARS-CoV-2 nucleic acid is detectable long after the resolution of symptoms in a significant percentage of previously diagnosed individuals, which is important to consider when interpreting PCR swab results. Persistence of PCR positivity does not correlate with antibody strength or symptoms of COVID-19. If anti-spike antibody is used to assess CP potency, individuals who suffered severe COVID-19 disease symptoms may represent better donors.

FIGURE 1

Nasopharyngeal (NP) swab positivity after symptom resolution. Percent positive NP swabs during each week‐long period post symptom resolution is shown for the donor population overall (A) and broken down into donor age groups (B)

FIGURE 2

Diarrhea and Loss of Taste/Smell. Neither the presence nor absence of diarrhea or loss of taste/smell showed a statistically significant association with the positive NP swab rate during each time period (≤21, 22‐28, 29‐35, 26‐42, 43‐49, and ≥50 days post symptom resolution). For loss of taste/smell, P values were .28 and .14 during the 22‐28 and 29‐35 day time periods, respectively (Fisher exact test)

FIGURE 3

Correlation between serology results and donor factors. Cutoff indices are shown for Beckman SARS‐CoV‐2 IgG Antibody Assay (white), Roche SARS‐CoV‐2 Total Antibody Assay (light gray), and Diasorin SARS‐CoV‐2 IgG Antibody Assay (dark gray) relative to select patient characteristics. With the IgG assays, patients hospitalized or who received treatment had a statistically significant increase in cutoff index values, which was not seen with the total antibody assay (A and B). Increasing age was positively correlated with increasing cutoff indices for the Beckman IgG assay (C). Increasing symptom duration was found to be positively associated with increasing cutoff indices measured in the total antibody assay, but not for the IgG specific assays. Antibody reactivity for individuals with symptom duration less than verses greater than 28 days is shown in D