Relationship of the Cycle Threshold Values of SARS-CoV-2 Polymerase Chain Reaction and Total Severity Score of Computerized Tomography in Patients with COVID 19

Karahasan Yagci, Ayşegul; Can Sarinoglu, Rabia; Bilgin, Huseyin; Yanılmaz, Özgür; Sayın, Elvan; Guneser, Deniz; Öncü, Mehmet Mucahit; Kartal, Zahide Doyuk; Can, Barıs; Kuzan, Beyza Nur; Bülent, Aslan; Korten, Volkan; Cimsit, Cagatay

Aim There are limited number of studies analyzing viral load in COVID19 patients and any data that compare viral load to chest computerized tomography (CT) severity. This study aims to evaluate the severity of chest CT in reverse transcriptase polymerase chain reaction (RT-PCR) positive patients and factors associated with it. Methodology SARS-CoV-2 RNA was extracted from nasopharyngeal swab samples by using Bio-speedy viral nucleic acid buffer. RT-PCR test was performed with primers and probes targeting the RdRp gene (Bioexen LTD, Turkey) and results were quantified as Cycle threshold (Ct) values. Chest CT of SARS-CoV-2 RNA positive patients (n: 730) in a period between March 22 and May 20, 2020 were evaluated. Total severity score (TSS) of chest CT ranged 0-20 was calculated by summing up degree of acute lung inflammation lesions involvement of each of the five lung lobes. Results Out of the 284 patients that were hospitalized, 27 (9.5%) of them died. In a total of 236 (32.3%) patients, there were no findings in CT and 216 (91.5%) of them were outpatients (median age 35). TSS was significantly higher in hospitalized patients although only 5.3% had severe changes. Ct values were lower among outpatients indicating higher viral load. An inverse relation between viral load and TSS was detected in both groups. CT severity was related with age and older patients had higher TSS (p < 0.01). Conclusion Viral load is not a critical factor for hospitalisation and mortality whereas outpatients have considerable amount of virus in their nasopharynx that makes them contagious to their contacts. Viral load is important to detect early stages of COVID-19 to minimize potential spread, whereas chest CT can help identify cases requiring extensive medical care.