Fig. 4.

Correlations of serum IL-6 levels measured on the day of recruitment with salivary cortisol levels measured during the next day in COVID-19 patients: a morning (8 a.m.), b mid-day (12-noon), c evening (6 p.m.), and d night (10 p.m.). Only the evening and night correlations were significant. COVID-19 patients are classified according to the severity of the disease (https://www.covid19treatmentguidelines.nih.gov/overview/clinical-spectrum/), and their clinical course during the 4-week follow-up period of the study, as mild-stable, moderate-stable, and moderate-progressed. Spearman’s rank correlation coefficient was used for associations between the parameters tested. *p < 0.05 is considered statistically significant. IL-6, interleukin-6