Nucleocapsid antigenemia in patients receiving anti-CD20 therapy with protracted COVID-19

Persistent SARS-CoV-2 infection: significance and implications

SARS-CoV-2 causes persistent infections in a subset of individuals, which is a major clinical and public health problem that should be prioritised for further investigation for several reasons. First, persistent SARS-CoV-2 infection often goes unrecognised, and therefore might affect a substantial number of people, particularly immunocompromised individuals. Second, the formation of tissue reservoirs (including in non-respiratory tissues) might underlie the pathophysiology of the persistent SARS-CoV-2 infection and require new strategies for diagnosis and treatment. Finally, persistent SARS-CoV-2 replication, particularly in the setting of suboptimal immune responses, is a possible source of new, divergent virus variants that escape pre-existing immunity on the individual and population levels. Defining optimal diagnostic and treatment strategies for patients with persistent virus replication and monitoring viral evolution are therefore urgent medical and public health priorities.

Impaired systemic nucleocapsid antigen clearance in severe COVID-19

The circulating nucleocapsid (NCP) antigen of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is detectable in coronavirus disease-2019 (COVID-19) patients. To better understand the biology of disease severity, we investigated NCP clearance kinetics in hospitalized COVID-19 patients. Serum NCP was quantified using a commercial NCP-specific enzyme-linked immunoassay in hospitalized COVID-19 patients (n = 63) during their hospital stay. Results were correlated to COVID-19 disease severity, inflammation parameters, antibody response, and results of SARS-CoV-2 PCR from nasopharyngeal swabs. We demonstrate that NCP antigen levels in serum remained elevated in 21/45 (46.7%) samples from patients in intensive care units (ICU) after >8 days postdiagnosis. The proportion of ICU patients with detectable antigenemia declined only gradually from 84.6% to 25.0% over several weeks. This was in contrast to complete NCP clearance in all non-ICU patients after 8 days, and also in contrast to mucosal clearance of the virus as measured by PCR. Antigen clearance was associated with higher IgG against S1 but not NCP. Clearance of NCP antigenemia is delayed in >40% of severely ill COVID-19 patients. Thus, NCP antigenemia detected after 8 days post COVID-19 diagnosis is a characteristic of patients requiring intensive care. Prospective trials should further investigate NCP antigen clearance kinetics as a mechanistic biomarker.

Investigation of Blood Plasma Viral Nucleocapsid Antigen as a Marker of Active Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Variant Infection

Background

Nasopharyngeal qualitative reverse-transcription polymerase chain reaction (RT-PCR) is the gold standard for diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, but it is not practical or sufficient in every clinical scenario due to its inability to distinguish active from resolved infection. Alternative or adjunct testing may be needed to guide isolation precautions and treatment in patients admitted to the hospital.

Methods

We performed a single-center, retrospective analysis of residual clinical specimens and medical record data to examine blood plasma nucleocapsid antigen as a candidate biomarker of active SARS-CoV-2. Adult patients admitted to the hospital or presenting to the emergency department with SARS-CoV-2 ribonucleic acid (RNA) detected by RT-PCR from a nasopharyngeal swab specimen were included. Both nasopharyngeal swab and a paired whole blood sample were required to be available for analysis.

Results

Fifty-four patients were included. Eight patients had positive nasopharyngeal swab virus cultures, 7 of whom (87.5%) had concurrent antigenemia. Nineteen (79.2%) of 24 patients with detectable subgenomic RNA and 20 (80.0%) of 25 patients with N2 RT-PCR cycle threshold ≤ 33 had antigenemia.

Conclusions

Most individuals with active SARS-CoV-2 infection are likely to have concurrent antigenemia, but there may be some individuals with active infection in whom antigenemia is not detectable. The potential for high sensitivity and convenience of a blood test prompts interest in further investigation as a screening tool to reduce reliance on nasopharyngeal swab sampling and as an adjunct diagnostic test to aid in clinical decision making during the period after acute coronavirus disease 2019.