Journal Article

Stringent thresholds in SARS-CoV-2 IgG assays lead to under-detection of mild infections

Hatch, Stephanie B., Stoesser, Nicole E., Marsden, Brian D., O’Donnell, Denise, Conlon, Christopher P., Jeffery, Katie, Eyre, David W., Ebner, Daniel, Cornall, Richard J., Lumley, Sheila F., Crook, Derrick W., Screaton, Gavin, Howarth, Alison, Cox, Stuart, Walker, Timothy M., Stuart, David I., James, Tim, Matthews, Philippa C., Peto, Timothy E. A.

2021

Overview

Background Thresholds for SARS-CoV-2 antibody assays have typically been determined using samples from symptomatic, often hospitalised, patients. In this setting the sensitivity and specificity of the best performing assays can both exceed 98%. However, antibody assay performance following mild infection is less clear. Methods We assessed quantitative IgG responses in a cohort of healthcare workers in Oxford, UK, with a high pre-test probability of Covid-19, in particular the 991/11,475(8.6%) who reported loss of smell/taste. We use anosmia/ageusia and other risk factors as probes for Covid-19 infection potentially undiagnosed by immunoassays by investigating their relationship with antibody readings either side of assay thresholds. Results The proportion of healthcare workers reporting anosmia/ageusia increased at antibody readings below diagnostic thresholds using an in-house ELISA ( n  = 9324) and the Abbott Architect chemiluminescent microparticle immunoassay (CMIA;  n  = 11,324): 426/906 (47%) reported anosmia/ageusia with a positive ELISA, 59/449 (13.1%) with high-negative and 326/7969 (4.1%) with low-negative readings. Similarly, by CMIA, 518/1093 (47.4%) with a positive result reported anosmia/ageusia, 106/686 (15.5%) with a high-negative and 358/9563 (3.7%) with a low-negative result. Adjusting for the proportion of staff reporting anosmia/ageusia suggests the sensitivity of both assays in mild infection is lower than previously reported: Oxford ELISA 89.8% (95%CI 86.6–92.8%) and Abbott CMIA 79.3% (75.9–82.7%). Conclusion Following mild SARS-CoV-2 infection 10–30% of individuals may have negative immunoassay results. While lowered diagnostic thresholds may result in unacceptable specificity, our findings have implications for epidemiological analyses and result interpretation in individuals with a high pre-test probability. Samples from mild PCR-confirmed infections should be included in SARS-CoV-2 immunoassay evaluations.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Adult / Ageusia / Ageusia - virology / Anosmia / Anosmia - virology / Antibodies / Antibodies, Viral - analysis / Asymptomatic / Asymptomatic Infections / Chemiluminescence / Coronaviruses / COVID-19 / COVID-19 - diagnosis / COVID-19 Serological Testing - standards / Diagnostic systems / Diagnostic tests / Enzyme-linked immunosorbent assay / Enzyme-Linked Immunosorbent Assay - standards / Epidemiology / Ethics / Ethnicity / Female / Fever / Health aspects / Health care / Health Personnel / Hospitals / Humans / Immunoassay / Immunoassay - standards / Immunoassays / Immunoglobulin G / Immunoglobulin G - analysis / Infections / Infectious Diseases / Internal Medicine / Male / Measurement / Medical Microbiology / Medical personnel / Medical research / Medicine / Medicine & Public Health / Microparticles / Middle Aged / Olfaction / Olfaction disorders / Pandemics / Parasitology / Research Article / Risk analysis / Risk factors / SARS-CoV-2 / Sensitivity / Sensitivity and Specificity / Serology / Severe acute respiratory syndrome coronavirus 2 / Smell / Taste disorders / Thresholds / Tropical Medicine / Undiagnosed Diseases / United Kingdom