In our study, 1318 patients who had a definitive diagnosis of Covid-19 by RT PCR were evaluated. 599 of them had mild to moderate disease and were treated on an outpatient basis and followed up. 719 cases had the severe or critical illness and were hospitalized.
In our study, the mean age was 48.81 ± 18.4 years and 51.9% were female. In the study of Mohsen Rokni et al., which was performed on 233 hospitalized patients, the mean age was 49.8 years and 64% of them were male [19]. Also, in the study of Soare Fucio Klinger et al., who performed on 875 hospitalized patients, the median age was 48 years (range, 2–97 years) and 50.9% of patients were female [20]. In the study of A Derviro et al., which was performed on hospitalized patients, the mean age was the median age of 72 (IQR 62.5–83.5) years and 64.4% of patients were male and the mortality rate was 28.7% [21]. In the study of Victor M et al., which was performed on 2511 hospitalized patients, the mean age was 62.7 ± 19 years and 50.9% were male and 8.6% were hospitalized in ICU and 11.6% died [22]. In the study of Barrett et al., which was performed on 1123 hospitalized patients, the mean age was 62 ± 16 years [23]. Comparing the results of these studies, the difference can be in the samples. In our study, we included both inpatients and outpatients, while in the mentioned studies, only inpatients were examined. There was no significant difference between men and women in previous reports and this shows the similarity of age and sex of patients in different studies.
In our study, the mean age of patients with mild to moderate severity, hospitalized patients who recovered, and hospitalized patients who died were 38.27 ± 13.62, 53.36 ± 15.58, and 66.49 ± 17.14 years, respectively. That is, the severity of the disease increased with age. A study by Ghweil et al. found that severe illness was more common in the elderly and mild cases occurred at a younger age. The mean age of patients was 62.6 ± 0.1 years in severe cases and 55.5 ± 10.1 years in mild cases [24]. Similar results were reported in the study by Liu et al. That is, the risk of severe disease in older age is higher than younger ages [25]. In the study of Mohase et al. and Yang Ell et al., the severity of the disease was also reported in the elderly [26, 27]. In a study by Javanian et al., older age was reported to be effective in mortality [28]. Also, in the study of Wang et al., old age was expressed as a worse prognosis in patients with Covid-19 [29]. The reason why the severity of the disease increases in old age may be due to decreased cell-mediated immune function and decreased humoral immune function. Also, in old age, the duration of the inflammatory process is longer and leaves more serious complications [30]. The prevalence of underlying diseases is also higher in old age [31], so the more severe disease in old age can be justified by these reasons.
Mortality in patients in our study was also assessed in terms of gender, which was not significantly different. Some studies have found gender to be effective in the mortality of Covid patients and have reported higher mortality in men than women [3], which is inconsistent with the results of our study.
In our study, the CT value in all patients was 26.8 ± 4.43 and in patients with mild to moderate severity who were treated on an outpatient basis was 27.45 ± 4.55 and in cases of severe and critical disease who recovered or died were 26.37 ± 4.41 and 26.05 ± 3.93, respectively. As the numbers show, it is inferred that the load of the virus in outpatients is lower than in the other two groups. Although there was a difference in hospitalized patients, this difference was not significant. In the study of Zeng et al., the viral load was reported to be higher in patients with severe infection [32]. In the study of Magleby et al., the viral load was higher in elderly patients [33]. In the study of Liu et al., the CT value was reported higher in patients with a severe infection than patients with milder infection [18]. In the study of Zhou et al., the median CT value in the incubation period was reported higher than the time of hospitalization [34]. In the study of Faico-Filho et al., The Faico-Filho et al. reported a U shape pattern for CT value. That is, in patients with mild disease severity and in severe cases of disease, the viral load was higher than in cases with moderate severity. In the same study, the CT value in different age groups was not significantly different [20].In the study of He et al., the amount of viral load in patients with different intensities was not different [35]. Based on the results of our study and some reports, it seems that a decrease in CT value as an indicator of virus load was more associated with an increase in disease severity. In our study, no correlation was found between CT value and age, and sex of patients. In the study of Taziki et al., the CT value of the age groups did not differ significantly [36].
In our study, the relationship between CT value and mortality of hospitalized patients, ie cases with the severe and critical disease, was investigated, but no significant difference was observed. In the study of Magleby et al., the viral load at the time of admission was reported independent of the probability of death [33]. The study by Yagci et al. and Faico-Filho et al. reported a similar result [12, 20]. In contrast, other articles have reported different results. In the study of Faico-Filho et al., a lower CT value was reported along with increased mortality risk [20]. A study by Magleby et al. had shown a similar conclusion [33]. The difference in these results may be due to the different design of the study or the prevalence of some underlying factors in the severity of the disease that had affected the mortality. In our study, there was no significant difference between the CT values of hospitalized or dead patients and the length of hospitalization time. In the study of Magleby et al., the amount of viral load at the time of admission was reported independent of the possibility of intubation [33]. In the study by Faico-Filho et al., survivors had higher CT values than those who died (27 vs. 21) [20], which is inconsistent with our study results. The difference in these results may be due to other factors influencing the outcome of the disease.
There are several reports about the relationship between HIV, Ebola, and Influenza viral load as a predictor of disease severity and progression of infection or its outcome [37–39]. Of course, some results were not conclusive [40]. However, SARS-Co-2 decreases the absolute amount of lymphocytes and increases inflammatory markers such as CRP and IL6, which is associated with worsening of the disease [41]. This finding has also been reported by Zhou et al. [30]. Also, the CT value can be affected by the sampling location, the experience of the person taking the sample, because usually samples taken from sputum have a higher viral load than samples taken from the throat [42]. Viral infections have been reported to cause an increase in acute phase reactants and can induce severe systemic inflammatory reactions that are known as cytokine storms [43]. These reactions are higher in patients with the severe disease than in mild or moderate cases and have been reported to be associated with disease severity [44].
In our study, the mean age of patients with severe disease who recovered slightly decreased from the onset of the pandemic to the time of this study, but the mean age of patients who died during this period did not change. Also, the sex distribution of patients showed that in the number of dead hospitalized patients before July, the frequency of women was more than men, but after this date, the frequency of men was always higher than women, and this ratio was still present for recovered hospitalized patients. The mean CT value did not change significantly during this period. Although these changes have not been significant, in many other cases the behavior of the virus in terms of severity, prevalence, and clinical symptoms have changes that can be influenced by environmental or genetic factors of the virus and need further study. Some limitations of this study in generalizing the results should be considered. In both groups of outpatients and inpatients, PCR test was performed only once and at the time of referral and it was not possible to repeat the test during hospitalization or a specific period.