The data set used in this study was collected from the date of onset of the COVID-19 pandemic from February 22, 2020, to 13 February 13, 2021 from the MCMC hospital registration system. During this period, Iran has identified three waves of the COVID-19 pandemic with the predominant strain of the Wuhan virus, along with the fourth COVID-19 wave in late February 2021. This study described the clinical features and hospital survival of patients based on age, gender, and severity of COVID-19 during the 12 months following the onset of the pandemic.
Our analyses showed that out of 24563000 patients with COVID-19, admitted until February 13, 2021, 2185 patients (8.9%) died, and the median survival of the hospital was estimated to be 21 days using the Kaplan-Mayer method. Also, 2559 patients (13.1%) were identified as severe cases of COVID-19. The majority of patients were admitted with a positive PCR test. As observed, the gender distribution of COVID-19 was similar to other studies, with men were more affected than women(6, 17). According to the systematic review and meta-analysis report on 15828 cases of COVID-19, the prevalence of severe and critical cases was 17.84% and 4.9%, respectively(7). However, our study showed lower values (13.1%), which may be due to the lack of data related to the hospitalization in the intensive care unit. The severity and hospital mortality of COVID-19 were also affected by gender (18). In line with other studies, men experienced a worse prognosis than women(19, 20).
The World Health Report has shown 3.0-8.35 higher mortality rate for men than women(21). Also, according to evidence from different studies, biological differences in gender affect the severity and outcomes of COVID-19, with men experiencing more severe and worse outcomes (22–24). Our data also showed that the risk of severe cases of COVID-19 was higher in men than women, although there was no significant difference (Table 1). Our findings showed that the mean age of male and female patients was the same, but the mean age of patients with severe cases and those who died was significantly higher with an average of 14 and 16 years, respectively, for non-severe and recurrent cases. Besides, the mean age men who died was significantly 2 years higher than the age of the deceased women, highlighting the role of age in the severity of COVID-19 outcomes in line with other studies (20, 25). Also, differences in age, gender, ethnicity, geographical location, and social and cultural structure affect the severity of the disease and its mortality(26, 27).
Our data showed that the most common underlying diseases in hospitalized COVID-19 patients were diabetes, hypertension and heart disease(28, 29). which is consistent with the reports of previous studies. Also, the prevalence of underlying cardiovascular diseases, hypertension, diabetes, asthma, and congenital diseases was significantly higher in women than in men. A meta-analysis of 28 studies from February 2020 to April 1, 2020 reported that underlying diseases increased the severity of COVID-19 by 3 to 18 times(30). Our findings, similar to the report of previous studies, showed that people with cerebrovascular diseases, cardiovascular disease, chronic lung disease, cancer, diabetes, and hypertension (6, 20, 30) were more at risk of severe COVID-19 cases than others(30).
Our findings, similar to other previous studies, showed that the most common clinical symptoms were fever, cough, and shortness of breath(2, 6, 31, 32).
The prevalence of clinical symptoms of fever(33), anesthesia, and headache was significantly higher in men, while women reported higher prevalence of chest pain, nausea, vomiting, muscle pain, plegia, dizziness, and skin symptoms. The proportion of respiratory symptoms (74.5%) was higher than gastrointestinal (17.9%) and neurological symptoms (0.9%), while the neurological symptoms were more prevalent in severe cases of infection (29.3%). In general, respiratory, gastrointestinal, and neurological symptoms were more common in men than in women, but the prevalence of clinical symptoms was not affected by gender. Wang et al. reported that clinical signs of fever, cough, and chills were more common in men. About 35% of patients reported a history of contact with COVID-19 patients, with men showing a significantly higher likelihood for such a contact than women. Besides, 43.3% of patients experienced severe cases of the disease had exposed to COVID-19 patients(34). Another study in the early stages of the epidemic in China reported that 23% of severe cases had a history of exposure to areas of epidemic onset(18). Another preliminary study from China also reported that 72.3% of those infected were in contact with Wuhan residents(35). In another study, Hong et al. found that 70% of patients had a history of close contact with the COVID-19 patients(34). The results showed that people who had close contact with the patients two days before and three days after the onset of the symptoms were 3.1 times more likely to be at high risk(36). Compared with asymptomatic patients, those who were exposed to patients with mild symptoms were 4 and 3.4 times more likely to be at risk than those exposed to moderate cases of the disease(36). The results showed that the patient's viral load decreased to its maximum 2 days before the onset of symptoms and after one week(36).
Our results showed that the prevalence of severe cases of COVID-19 was significantly higher in patients with than those without a previous history of the COVID-19 infection. Studies have shown that the cause of the COVID-19 re-infection has been the emergence of new genetic strains, with CDC (2020) reporting a 45-day interval between re-infections(37) and Tang et al. reporting 19 days(38). Our findings showed that patients with a history of previous COVID-19 infection were older (45.5% vs. 37.6%) and had a history of comorbidities, including diabetes (21.8% vs. 13.7%), hypertension (21.2% vs. 14.3% ), and cardiovascular disease (15.8% vs. 7.8%), which confirms our findings given the emphasis of other studies on the role of age of comorbidities(25, 39, 40) in increasing the severity of COVID-19.
Duration of hospitalization has been reported based on the average or median in different studies. The average duration of hospitalization in our study was about 5 days and in the scope of world studies. Also, using the Kaplan Meier method, the length of hospital stay in our study was estimated to be 21 days(41). In a study by Nirmala, while, the average length of hospital stay was between 4 to 53 days in 45 hospitals in China and 4–21 in studies outside China as found in a meta-analytical study with 52 studies (46 studies from China)(41) Also, the median length of hospital stay was 7 days (in a study from Iran(42), 12 days in a study by Nirmala (43), and 12.4 days using the AF methods(44).
We found that the length of hospitalization of COVID-19 patients was influenced by gender. Consistent with other studies, our results showed that the duration of hospitalization was longer in severe than non-severe cases(25), with patients who experienced severe cases of COVID-19 hospitalized 3 days more than those without severe COVID-19. The length of hospitalization has been reported differently in various studies, and factors such as the severity of the disease, the time from the onset to the diagnosis, age over 45 years, residential area(45), previous underlying medical conditions, and the location of the infection(46) affect the length of hospital stay of COVID-19 patients.
Our findings showed that the majority of patients had a respiratory rhythm of 14–18 beats per minute, with a higher respiratory rhythm in men at all respiratory levels than in women. However, there was no significant relationship between gender and respiratory rhythm. Also, cases of severe COVID-19 increased significantly with an increase in respiratory rhythm, indicating a respiratory rhythm above 28 beats per minute for 5.5% of severe cases. CT scans also showed about 91% of patients with lung abnormalities, but no gender differences were observed in lung involvement. Our findings showed that the results of positive CT scans of patients with severe cases of COVID-19 lung involvement were significantly higher than those of patients with negative CT scans. One of the most important tools for the assessment of COVID-19 severity is the CT scan results of the lungs(25). Studies have also shown that the respiratory pattern in COVID-19 is not similar to that of the flu and cold, according to which people with COVID-19 have faster breathing due to shortness of breath(6, 36).
Liu et al. noted that patients with severe COVID-19 infections were more prone to faster respiration(6) and higher respiration rates. According to another study, a decrease in the vital respiratory capacity was observed in 65.4%, while 18.8% of patients represented an abnormal respiratory pattern(36). Our findings showed that severe cases of COVID-19 were more susceptible to oxygen therapy than non-severe cases (P < 0.001).
Previous studies have reported that decreased blood oxygen levels were associated with increased severity of COVID-19(6, 39). Evidence from studies has shown that the objective symptoms of respiratory distress - oxygen saturation and respiratory rate - are associated with worse outcomes, such as a significant increase in mortality(25). Chatterjee et al. reported that the chance of mortality in patients with a respiratory rhythm of > 22 beats per minute was 2.3–9.1 times higher than in patients with a normal respiratory rhythm (< 20 beats per minute)(25). The results of these studies confirm our epidemiological findings.
The mean body temperature of men compared with women and the body temperature of patients with severe COVID-19 also increased significantly compared to those without severe infections. One of the most common clinical signs of the COVID-19 infection is fever, which leads to an increase in body temperature(47, 48) and can be considered one of the screening tools to diagnose COVID-19 infection in communities(48). Wang et al. reported that severe cases of COVID-19 increased significantly in patients with febrile symptoms(48), while another study reported that severe cases of COVID-19 had higher body temperature(6). In another study, it was reported that the mortality rate in patients with an average body temperature of more > 40 ° C was 42% (49) that confirms our findings.
About 5% of the COVID-19 patients admitted to the hospital received treatment with mechanical ventilation, with a significantly higher percentage of men (5.2%) than women (4.6%) treated with mechanical ventilation. In other studies, age was high in patients undergoing mechanical ventilation, and elderly patients suffered from underlying diseases, etc.(50). Our data showed that patients treated with mechanical ventilation were on average 9 years older than those without mechanical ventilation treatment, while the prevalence of underlying diseases was also higher in patients treated with mechanical ventilation. Patients treated with mechanical ventilation experience higher mortality(51). Consistent with our study, mortality was higher in patients with severe COVID-19. Men also experienced more cases of COVID-19 than women on dialysis.
The results of our study showed that most cases occurred in the third wave of COVID-19 (50.1%) with 12318 infections, according to which the distribution of severe cases of COVID-19 decreased significantly from (11.8%) in the first wave to 9.8% during the second wave. It then increased during the third wave (74%) and then decreased significantly at the beginning of the fourth wave (4.3%) in late February (p < 0.001). However, the gender distribution did not differ significantly during the COVID-19 pandemic waves, and there were no significant differences in men and women concerning the risk of severe cases. The risk of severe cases of COVID-19 in patients admitted during the third and early fourth waves of COVID-19 increased significantly by 67.2% compared to the first wave. In addition to mutations in the COVID-19 virus and changes in its transmission, other factors such as social events, the end of quarantine, gathering in enclosed places, etc. led to numerous waves of COVID-19 in many countries with different intensities and characteristics(1). A study in Spain reported that the number of hospitalizations increased from 204 in the first wave to 264 in the second wave(1). On the other hand, the duration of hospitalization in the second wave was shorter than in the first wave(1).
According to our findings, the median length of hospital stay was estimated to be 21 days by the Kaplan-Meyer method. Based on the results of the color lag test, the duration of hospitalization decreased significantly from 25 days in the first wave to 19 days in the third and 15 days in the early fourth wave in late February. We observed an increase in the incidence of severe coronary artery disease in patients admitted during pandemic waves. Our analysis showed that the risk of severe cases was 1.654 and 2.148 times higher than the first wave of COVID-19 in the third and early fourth wave to the end of February 2021 (P < 001.0). Also, the risk of severe cases of COVID-19 was 2.1 times higher in patients aged \(\ge 65\) years than younger people (P <0.001). In this study, we described the clinical features of patients hospitalized with COVID-19, and we need to further investigate the important factors affecting the severity and mortality.