Open AccessCorrelation between cycle threshold and viral load through comparison of RT-PCR qualitative <em>versus</em> quantitative assay for SARS-CoV-2
Author(s) -
Angela Saraiello,
Federica Ferrentino,
Nunzia Cuomo,
Maria Grimaldi,
Erasmo Falco,
Marcello Raffone,
Antimo Di Spirito,
Nazareno Melillo,
G Montanino,
Valentino Guarino,
Francesco Nappo,
Maria Rosaria Esposito,
Ilaria Cavallaro,
Giovanni D’Auria,
Luigi Atripaldi,
Claudia Tiberio
Publication year - 2021
Publication title -
microbiologia medica
Language(s) - English
Resource type - Journals
eISSN - 2280-6423
pISSN - 1120-0146
DOI - 10.4081/mm.2021.9999
Subject(s) - viral load , real time polymerase chain reaction , covid-19 , correlation , gold standard (test) , spearman's rank correlation coefficient , medicine , virology , respiratory system , virus , biology , immunology , gene , statistics , disease , infectious disease (medical specialty) , genetics , mathematics , geometry
Background and aims. Real-time reverse transcription polymerase chain reaction (RT-PCR) is the gold-standard assay to detect SARS-CoV-2, but it has limitations compared to viral load analysis. Quantitative detection improves surveillance, diagnosis, and prevention. We performed a comparative study of qualitative and quantitative tests for the diagnosis of COVID-19 on respiratory samples from patients screened for SARS-CoV-2 infection, and explored the correlation between viral load compared to the threshold cycle (Ct) value obtained in RT-PCR.Materials and methods. Sixty respiratory samples from patients affected by SARS-CoV-2 were subjected to both the qualitative (Allplex ™ 2019-nCoV Seegene) and the quantitative (Clonit® Quanty COVID-19) assays, and the relationship between viral load and Ct value was assessed by Spearman correlation analysis (ρ). In addition, the viral load of samples collected from a patient with symptomatic cancer was monitored. Results. The results show 100% agreement between the results obtained with quantitative assay and the reference standards, whereas 99.2% agreement was found for the qualitative test. A strong negative Spearman’s correlation between the Ct values of the N genes and RdRP gene was observed from qualitative assay values and viral loads.Conclusions. Quantitative assay has a higher sensitivity than qualitative assay, and viral load testing allows the clinicians to better orient themself in the choice of therapeutic treatment to be adopted. The constantly higher viral load of clinical cases considered, irrespective of the different therapies used, confirms that viral load monitoring could represent a great advantage in clinical practice.