The aim of this study was to specify the effect of prognostic factors on the survival of COVID-19 patients using a proportional hazard cox model. Based on our results, the overall 1, 5, 10, 20, 30 and 49-day survival rate were 99.57%, 95.61%, 91.15%, 87.34%, 86.91%, and 86.74% respectively. In addition, we found a significant association between survival time and age, gender, history of traveling to contaminated areas, having underlying disease, malignancies, and chronic diseases, and hospitalization sector.
The present study indicated that elderly patients with COVI-19 had the highest mortality rate and lowest survival rate. This finding is concordance with the previous studies which demonstrated a higher mortality rate between the elderly populations (10, 11). Principally, elderly people have a weak immune response to infectious agents, and therefore, are more susceptible to severe infection (12). On the other hand, the prevalence of bacterial infection and underlying diseases such as diabetes, hypertension, cardiovascular disease, and cerebrovascular disease is higher in the elder population than in young and middle-aged patients, which puts them at higher risk of COVID-19 infection and its adverse consequences including death. Additionally, in Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) diseases, aging has been introduced as an important independent risk factor for mortality (13).
Our findings showed that the median and mean survival time is significantly lower in men than in women. Epidemiological studies show sex-specific differences in the incidence and mortality rates in humans after COVID-19 infection, with males experiencing a higher mortality rate compared with females (14). Previous Investigations showed that men manifest more serious forms of the disease during the COVID-19 epidemic compared to women (14–16). This decreased vulnerability of women to viral infections may be attributed to the sex hormones and the X chromosome, which perform an essential role in innate and adaptive immunity (17). On another aspect, a higher incidence rate of COVID − 19 in men might be due to higher social interactions in workplaces. National office for statistics reported that men included 81 percent of the workforce in Iran during 2018-19; while more than 50 percent of them are employed in service occupations. Therefore, there is a higher possibility for men to obtain COVID − 19 infection due to higher social interactions in work environments (18).
Our findings revealed that the mortality rate of COVID-19 in residents of rural areas is higher than urban areas but their survival function is not significantly different. The high mortality rate in rural areas may happen because of factors correlated with poor access to healthcare or inadequate surveillance and monitoring in rural regions (19).
According to the present study, the mortality rate of COVID-19 in patients with underlying disease is four times higher than the healthy people. On the other hand, survival time in people with the underlying diseases is significantly shorter than people who do not have these diseases. Previous literatures showed that underlying diseases such as diabetes, hypertension, and coronary heart disease increased the risk of COVID-19 infection and subsequent adverse consequences such as hospitalization in invasive care units and death (3, 20). This occurs because of several mechanisms including direct damage by the virus, systematic inflammatory responses, and weakening the immune system. Consistent with our study in research conducted by Emami and et al patients with malignancies are more in danger for mortality from COVID-19 than those without any tumor (3). Anticancer treatments such as chemotherapy and surgery put this group into an immunosuppressive state and subsequently at higher risk of MERS-CoV-2 infection (21).
There were some limitations in our study. First, estimation of survival rate requires reliable sources of data obtained from the prospective design while we conducted a retrospective cohort study. Second, information about potential confounding factors was not available, such as access to health care insurance and the severity of the disease. Third, this study was performed in a specific geographic area of Iran. On the other hand, there might be some unknown genetic or environmental factors influencing the results; therefore, the findings might not be completely generalizable to other populations. Despite these limitations, the study author was able to use the estimated 20 and 49-day survival rates, measuring the time from symptom onset to outcome.