Our study is a nationwide study using the Korean HIRA database to evaluate several risk factors for mortality in adults in patients with COVID-19 in Korea. The mortality rate of patients with COVID-19 was 3.1%. Particularly, male, older age (>65 years), patients diagnosed with a large outbreak area, Medical Aid beneficiaries, higher CCI (≥3), hypertension, COPD, CHF, and ESRD were associated with high odds of mortality.
Previous studies have found that women are less susceptible to viral infection than men (9). Because X-chromosome and sex hormone influence the innate and adaptive immune responses to a pathogen. Simultaneously, men are more likely to have underlying diseases. As a result, the proportion of men with mortality is greater than that of women. Old age was a significant clinical predictor of mortality in SARS and MERS (10, 11). This study confirmed that old age was also associated with death in patients with COVID-19. The age-dependent defects in immunity function and the overproduction of type 2 cytokines could cause a deficiency in control of viral replication and prolonged pro-inflammatory responses and more likely to develop to poor outcomes (12). Daegu and Gyeongsangbuk-do province had the first large outbreak of COVID-19 in Korea(13). Korea is one of the countries with large outbreak to flatten the curve of the newly developed COVID-19. Although it has been performed without block strict specific areas and shutting down the economy, during this time, a shortage of inpatient beds, healthcare workers, and personal protective equipment in these areas might cause higher mortality rates than in other parts of Korea. In Korea, the Medical Aid system is a public assistance program that provides healthcare benefits to low-income patients. Medical Aid beneficiaries accounted for 2.9% of all Korea, whereas other Koreans were beneficiaries of National Health Insurance (14). In Korea, the cost of treatment is free of charge after the patients are diagnosed with COVID-19 regardless of the insurance status. In other words, Medical Aid beneficiaries, even if unrelated to the economic status of receiving treatment, fully implicated a risk factor of mortality in this study. Several studies reported that Medical Aid beneficiaries were possibly related to household poverty and had poor health status and a higher risk of chronic diseases compared to National Health Insurance beneficiaries (15). For these reasons, it is thought that Medical Aid Beneficiaries are a risk factor for the mortality
Circulatory, endocrine, and respiratory comorbidities were common among patients with COVID-19 in this study. Our findings have reflected recently published studies in terms of the similarity of comorbidities in patients with COVID-19(16-18). Consistent with previous reports, the percentage of patients with malignancy, ESRD, and IBD was low. These findings provide further objective evidence, with a larger sample size to consider baseline underlying diseases to evaluate prognosis among patients with COVID-19.
Several existing studies have reported risk factors for poor outcomes (age ˃65 years, male, hypertension, DM, COPD, malignancy, smoking, and cardiovascular diseases) among patients with COVID-19 admitted to the hospital (2-4). In our study, some risk factors were the same as those of previous studies, but DM, malignancy, and liver cirrhosis were not risk factors for mortality. Perhaps due to the characteristics of Korean medical services (easy accessibility and National Health Insurance Corporation Checkup), most patients with underlying diseases are diagnosed early and receive treatment; thus, there are many patients with COVID-19 who have less complications or have stable conditions of underlying diseases. In addition, this difference in risk factors is thought to have occurred because all patients diagnosed with COVID-19 were able to receive proper management according to severity free of charge after active rapid testing in Korea.
The clinical significance of our study is as follows. First, since large outbreaks become a risk factor for mortality, it is important to prevent large outbreaks in the area by social distancing, wearing masks, early detection through active diagnostic tests, contact tracing, and quarantine. Second, in the case of low-income patients, the mortality rate is relatively high, therefore, more active social support and interest are required. Third, in general, comorbidity may not exist alone, but two or more comorbidities may exist simultaneously in a patient. A recent study reported that patients with a greater number of comorbidities correlated with poorer clinical outcomes among patients with COVID-19(4). In this study, it was also confirmed that the mortality was significantly increased in patients with CCI ≥3.
This study had several limitations. First, all patients did not reach the study outcome or were discharged by the end of the study period. Second, due to the retrospective study design using the Korean HIRA database, all clinical data (symptoms, smoking history, BMI, and laboratory tests) were not available. In addition, the severity of comorbidities at the time of confirmation of COVID-19 could not be evaluated. Third, the diagnosis of comorbidities was based on the ICD-10 code. Therefore, the diagnosis of some comorbidities might not be optimal. Fourth, the Korean health care system was not disrupted, so it is free to use the health care system. ICU and ventilator capacity were not exceeded during the study period. Because the health care system and strategy of COVID-19 in each county are different, the above must be considered when interpreting our findings.