Quantitative Detection of SARS-CoV-2 RNA in nasopharyngeal samples from infected patients with mild disease.

Bustos, Patricia; Tambley, Carolina; Acevedo, Alejandra; Andrade, Winston; Leal, Gabriel; Vidal, Deyanira; Roldán, Francisco; Fasce, Rodrigo; Ramírez, Eugenio

Diagnosis of SARS-COV-2 cases is based on the count of real-time RT-PCR positive people. Viral load by real-time RT-PCR has been suggested as a biomarker of the SARS-CoV-2 infection. However, the association of viral load and severity of the disease is not yet resolved. Nasopharyngeal samples from 458 patients were tested by RT-PCR for SARS-CoV-2 diagnosis. Relative quantitation was made by the comparative threshold cycle (ΔΔCT) formula between ORF1ab viral and RNase P housekeeping genes. Absolute viral load was calculate using a reference positive control. Most prevalent clinical signs were cough (75.8%), myalgia (66.7%) and fever (48.5%). Hypertension (18.2%), neurological diseases (15.1%), and asthma and hypothyroidism (12.1%) were most frequent comorbidities. Fever, either as an exclusive symptom or combined with others, was associated with high viral loads (2ΔΔCt range 35.65-155.16; 4.25-4.89 log10 RNA copies/test]). During the first week after onset of symptoms in mild patients up to 60 years-old was detected the peak of viral load. Children under 10 years-old have a high viral load (313.84; 2.50) in the first two days post-infection with a sharp decline thereafter. Cases between 10 and 49 years-old mostly showed low and moderate viral load during the first two days post-infection (range 0.03-17.24; -1.50-1.24). Patients over 60 years-old have high viral load up to the second week after the onset of symptoms (range 25.32-155.42; 1.40-2.19), indicating the longer presence of the virus in them. These findings suggest the viral load in nasopharyngeal swabs would help to monitor the SARS-CoV-2 infection in mild COVID-19 cases. This article is protected by copyright. All rights reserved.