SARS-Cov-2 Cycle Threshold Value and Olfactory Dysfunction in COVID-19 Patients

Considering the inconsistent results regarding the association between the severity and duration of olfactory dysfunction (OD), and the viral load in coronavirus disease 2019 (COVID-19) patients, we aimed to conduct this study.

This is a prospective cohort study in which COVID-19 patients were evaluated for the initial cycle threshold value (Ct values) measured by the nasopharyngeal samples along with olfactory function measured by the University of Pennsylvania Smell Identification Test (UPSIT) within 2 months of COVID-19 onset.

Among 309 COVID-19 patients who were included in this study, 108 (34.9%), 112 (36.2%) and 89 (28.8%) were normosmic, hyposmic, and anosmic, respectively based on the UPSIT. The severity of COVID-19 and the rate of hospitalization were higher in anosmic patients (p<0.0001, and p<0.0001, respectively). Moreover, significant associations between the initial Ct value and the severity of OD at admission and follow-ups were detected (p<0.0001 and p<0.0001, respectively). Anosmic patients had higher Ct values in comparison with hyposmic (approx. 3-fold) and normosmic (approx. 12-fold) patients. The recovery rate after one- and two-month follow-ups was 47% and 84%, respectively. At the follow-ups, OD-recovered patients significantly had lower Ct values (mean Ct value: 27.79 ± 2 and 28.21 ± 2.08) in comparison with those who have not recovered yet (mean Ct value: 30.19 ± 3.36, and 33.6 ± 3.37) (p<0.0001, and p<0.0001, respectively).

Ct value seems to be a significant factor not only in predicting OD severity in COVID-19 patients but also in the OD recovery duration. This finding may be helpful to investigate the underlying mechanisms of OD in COVID-19 patients.